I discovered the mite Histiostoma palustre in 2000 (and reared it at least until 2001) in the Berlin gravelpit area „Im Jagen 86“ at about 52°29’18.7″N 13°14’28.2″E and published the description in 2002 (2003). It is phoretically associated with at least two Hydrophilidae beetle species in bank mud (sapropel) around (in times of the sampling several) ponds. The phoretic juvenile instar deutonymph attaches its host insect to be carried that way to a new suitable habitat.
Phoretic hosts and attachment site
I in those times determined two host beetles as belonging to the genera Coelostoma and Cercyon. In laboratory host choice tests, in which deutonymphs in a culture had the choice between three different potential host species, there was a significant preference for those Hydrophilidae beetles, while another offered beetle species sympatrically living the same habitat was almost not at all attractive for the phoresy instar. But the choice test was performed as a smaller side project only and offered not more than a host tendency, as for example not a representative variety of insect species from the same natural field habitat of the mite was involved in these choice tests. But indications were at least clear enough that a host specificy (on a higher taxonomic level) of H. palustre can be stated. Mites preferred according to these tests a specific area for attachment on their hosts, which was the dorsal head area.
Two different male types and the difference between polymorphism und polyphenism
The mite showed under laboratory conditions a male diphenism with highly modified gripping organs or normal legs2. While the modified leg can appear on both sides or only on the left or the right side.
„Polymorphism“ is used internationally as the overriding term for such a phenomenon. Here, following the teaching of my former research group at the FU Berlin, I distinguished between a purely genetically determined expression of distinctly deviating morphs and the determination of these morphs by the presence of certain environmental factors. In the latter case we are talking about polyphenism. Of course, genetics also play a certain role here additionally.
Studies with cultures grown at different temperatures suggested that males with modified legs 2 appeared significantly more frequently at higher temperatures than at lower temperatures.
Temperatures: 30-32 °C (measured in summer inside the culture dishes at room temperature) and 20°C (climate cabinet, temperature inside and outside the cultures almost equal). Experimental approaches and total numbers of males counted: 10 cultures with lower (don’t remember exactly) numbers of developing mite stages per each of the two different temperatures. n=237 males in total at low temperature, n=729 males in total at high temperature. The number of modified males grew significantly from 18% (20°C) to 45% (30°C), while normal males decreased significantly from 82% to 55%.
Therefore I called the mechanism for the formation of two morphs diphenism. These studies were also a besides project and the amount of data would need to be even bigger according to higher level statistical requirements.
About the function of the modified male legs
I could observe in the mite cultures in which H. palustre thrived very well on decomposing potato pieces at about 20°C room temperature that the modified legs of the heteromorphic males used as prehensile organs played a role in intraspecific competition for female mating partners. Here several males, with and without gripping organs, were usually wedged together in veritable clusters around female tritonymphs or adult females. This was because the fighting happened more or less in a slow motion speed with apparent longer lulls in between. During the fights, the legs of the opponents were seized with the prehensile organ and the competitor was slowly pulled away from the coveted female.
Less is known about which selective pressure would favor the morph with gripping organ
Males with normally developed legs were at least seemingly in my observations clearly at a disadvantage here, since their second legs in particular could be easily grasped and they were hardly capable of defense and counterattacks. Nevertheless, random counts at that time did not provide any clear indication that heteromorphic males were possibly found significantly more frequently in the final mating position. The same applies to expectations regarding an unequal sex ratio in favor of males. Instead, males and females appeared to be almost evenly distributed in random evaluations. Additionally males with modified legs on both sides and with only one modified leg on the right and the left were in randomly counted cultures seemingly equally distributed.
Still many questions unanswered about the biology of H. palustre
It was unfortunately not tested at all, whether females mated by heteromorphic males and those mated by homomorphic ones had different reproduction successes. In connection with this biologically highly interesting mite species, many questions about its life strategies could not be examined deep enough during times of my PhD thesis. There was no time for this, since my research at the time was geared towards systematic comparative studies of numerous species. Unfortunately, the species could so far not be found again in its habitat „Im Jagen 86“ – at least not by the means of substrate samplings with only accidental Hydrophilidae inside – until today so that further studies were not yet carried out. This seeming lack of the species‚ presence in its former habitat is probably due to ecological changes in this area, which originally had several ponds, from which now only one remained.
What makes this male diphenism interesting from the evolutionary point of view
Two distinct morphs within the same sex of a species is the result of evolution. It does at first not matter, whether it is a dimorphism or a diphenism. A fundamental question, which cannot be answered at this time, is: does the trait of these two morphs indicate that the species is on the way to finally having exclusively only males with prehensile organs, and is the species even on the verge of becoming the to cross the species boundary into a new species? Or is the characteristic of two male types a permanently stabled character, because exactly this has strong selection advantage?
In this context, fossil finds of closely related species (in amber) would be of interest, but unfortunately these are not yet known. It would also be interesting to compare different populations of this species, which are also not yet available. It furthermore would be of interest to understand, what exactly the advantage of modified males versus non modified males might be. Is it possible that an advantage of the modified-legged males is simply that they copulate more frequently, although smaller datasets have not yet confirmed this? And/or do females mated by modified males produce significantly more offspring?
And in the special context of the knowledge at that time that it is a temperature-dependent diphenism, one could raise the question of whether the species „evolutionally prepared itself“ by developing two male forms to cope better with temperature fluctuations. In view of increasing global warming, this may be of general biological interest.
A similar species from Egypt
A publication about a species with modified legs 2 as in H. palustre
In a conference proceedings contribution Bishlawy, S. E. M. O., and S. F. M. Allam published an article containing the description of a species of Histiostomatidae, which the authors have named Histiostoma egypti ( Proc.2nd Inter.Conf.Ent.Soc.Egypt, vol. 1, pp. 407-420, 2007). This is worth of being mentioned here more detailed in context of a possible close relationship of these species or a convergent evolution. But due to the lack of systematic facts, a decision hypothesis is not yet made. I can just emphasize that one showed me photos of that species on a conference in Cairo (Egypt) in 2003, and my first and superficial interpretation was that it even isHistiostoma palustre.
I have not checked whether the species Histiostoma egypti has been accepted internationally as a new species and is therefore also listed in the Zoological Record, as this is not relevant to the considerations here. It is interesting that a similar species was discovered in Egypt, about which there are some biological observations.
However, I only have a text version without illustrations, which is online published like that and which is why I cannot assess this species systematically/taxonomically on a deeper level. The authors refer to a similarity of their species with Histiostoma palustre including a similar diphenism of the males. I, as I already mentioned above, remember confirming this resemblance at an acarological conference in Cairo in 2003, where the co-author showed me photos of the later H. egypti.
Association with laboratory cultures of entomopathogenic nematodes
According to the authors, the species entered the laboratory with entomopathogenic nematode substrate and is doing well in the nematode cultures. The mite species is called semiaquatic, which quickly dies off at lower humidity. According to the authors, the thriving of the mites is to the detriment of the nematodes, which can die as a result. In this context, the authors mention having observed that the heteromorphic male form appears more frequently when live nematodes are present, while the homomorphic form and also the phoretic deutonymphs predominate when previously present nematodes have died.
My general experiences with histiostomatid mites and free living (phoretic) nematodes
A connection between the development of different mite morphs and the presence or absence of living nematodes never became particularly obvious to me in my studies at the time on species with different male types. Therefore, I have never specifically investigated such a connection and can therefore judge the correctness of such a connection as neither improbable nor very probable.
I can confirm, however, that basically all Histiostomatidae species that I examined always appeared together with nematodes, which were usually free-living, microorganism-eating representatives of the Rhabditidae or Diplogastrinae, which are also phoretic and possibly even were spread by the same hosts as the mites.
In this context, I am aware of the phenomenon that nematodes and mites can either compete with each other for food or reduce each other, for example chemically. In any case, it can often be observed that after some time in a culture vessel in which both animal groups were initially numerous, only the mites or the nematodes thrived in large numbers.
General information about the feeding behavior in Histiostomatidae
According to my recent research, based on frame-by-frame videographic analysis and SEM studies, Histiostomatidae species use their filter-feeding mouthparts to feed on decomposing fungal material that is also bacteria-rich. It is highly probable that the fungi are brought by the mites themselves into their habitat, which seems to happen hyperphoretically via fungal spores. The mites probably also control the growth and partial death of the fungus themselves in the form of their fungicidal gland secretions. Specific studies about the feeding behavior of H. palustredo not exist on a more advanced level. Slides and numerous SEM shots might indicate the transport of spores, but I so far had no time to examine those specimen closer. Such results thus need to be presented at another occasion.
Information about nomenclature used in the 2003 publication and about the citation of this species description
Nomenclature for dorsal/ventral setation of juveniles and adults used in this old species description of mite H. palustrewas my own invention and is no longer used by me for practical/systematic reasons of comparison.
The nomenclature I introduced at the time of that species description for the pattern of individual fields that cover the thickening of the cuticle (proterosoma shield) on the anterior dorsal side of the proterosoma is still retained by me to this day. I still consider this characteristic in adults to be systematically relevant.
The original species description is cited as a 2001 publication on the Acarologia abstract page and is cited as 2002 publication in the PDF of the article provided by Acarologia as open access publication. In fact it was accepted for publication in 2001 and finally published in 2003. Thus I sometimes cited it as 2003 publication, but 2002 would be a correcter citation too. At least the full species name must be Histiostoma palustre Wirth, 2002.
More Specialists are needed to study our biodiversity: recognizing and describing new species, redescribing known ones, mapping their distribution and understanding their ecological role in an ecosystem.Thus we have to support our children and students to become fascinated by nature.
Also interested laypeople, hobby researchers and nature lovers can contribute to species preservation and nature conservation (and thus climate protection) and encourage their children or relatives to study biology or a similar subject.
Es werden mehr Spezialisten benötigt, um unsere Biodiversität zu studieren: neue Arten zu erkennen und zu beschreiben, schon bekannte Arten neu zu beschreiben, ihre Verbreitung zu kartieren und ihre ökologische Rolle in einem Ökosystem zu verstehen. Daher müssen wir unsere Kinder und Schüler dabei unterstützen, sich für die Natur zu begeistern.
Auch interessierte Laien, Hobbyforscher und Naturfreunde können einen Beitrag zum Arten- und Naturschutz (und damit zum Klimaschutz) leisten und ihre Kinder oder Angehörigen für ein Studium der Biologie oder eines ähnlichen Faches animieren.
I provide advices and information about the topics mites (in general, in your house or your company and in a hygiennic context), biodiversity, correlation biodiversity research and climate change, speciation processes, describing new species, species extinction, taxonomy for private people, educational institutions, e.g. schools or university students. Please see my menue item „Angebot biologische Beratung…“
Ich biete Beratung und Informationen zu den Themen Milben (allgemein, in Ihrem Haus oder Ihrem Unternehmen oder im hygienischen Kontext), Biodiversität, Korrelation Biodiversitätsforschung und Klimawandel, Artbildungsprozesse, Beschreibung neuer Arten, Artensterben, Taxonomie, für Privatpersonen, Bildungseinrichtungen, z.B. Schulen, oder Studenten. Bitte beachten Sie meinen Menüpunkt "Angebot biologische Beratung..."
In biodiversity research, knowledge of species numbers is the basis for planning environmental protection and climate research. However, the taxonomic work is made more difficult by cryptic species complexes in the world of organisms. Careless determinations of similar species must be prevented. For a beter understanding, examples from different animal groups are given. Using two species complexes of the mite taxon Histiostomatidae (Astigmata), two different forms of cryptic species complexes are presented in detail. Based on three species from a group associated with bark beetles, an example of a species complex is presented in detail, in which all stages of development look confusingly similar to one another. On the other hand, four species of mites from the bank mud of standing waters can only be confused with one another on the basis of their phoretic dispersal stage (deutonymph), while the adults differ distinctly. The meaning of such species complexes is discussed in the evolutionary and applied context. It is critically pointed out that too few specialists are funded worldwide and few taxonomists have to work too quickly, so that there is a risk of cryptic groups of species not being taken into account in surveys.
Biodiversity research is an essential fundament for disciplines like climate research and climate changes and thus contributes to an understanding about, how we humans need to treat our own environments. A main aspect of biodiversity research besides species monitoring is the evaluation of how many species we have. Specialists need to recognize and scientifically describe new species, especially, when it for example comes out that a complex of very similiar species contains more species than expected before (e.g. Laska et al. 2018). In tendency researchers in the field of biodiversity focus most on vertebrates in temperate regions and generally less in invertebrates (Titley et al. (2017).
The number of recently existing species in numerous cases is still unknown, especially in taxa of small organisms, such as mites. Due to a lack of specialists and due to a lack of fundamental research fundings, relatively much is known about direct pests of human sources, such as Varroa or Tetranychidae mites. But within the major clade Acariformes, ecological contexts and numbers and distribution of species of some free living taxa of Prostigmata and Oribatida/Astigmata are still an open field, even in Central Europe, e. g. Germany (Wirth, 2004).
This is despite the fact that for example phoretic mites, which use other arthropods as carriers for dispersal, can have highly complex relationships with their phoretic hosts, thus being of interest from the evolutionary, the ecological and even an applied point of view. The latter is discussed for example in context with different bark beetles, which their mites might affect by acting as vectors for fungus spores (Klimov & Khaustov, 2018).
Cryptic species complexes are a topic that is currently being widely dealt with in science. Such species complexes are characterized by the fact that they are difficult or impossible to distinguish morphologically. However, they can be clearly differentiated from one another using barcoding (e.g. Kameda et al, 2007), behavioral or ecological studies. Crossing experiments are a frequently used ecological method. Because according to the biological species concept, individuals of different species either cannot be crossed with one another or the offspring of such a hybridization is not fertile (e.g. Sudhaus & Kiontke, 2007).
Crossing experiments are particularly suitable for the investigation of cryptic species complexes in species that have a rapid life cycle and, due to their small size, can be accommodated well in standardized conditions. Such organisms are, for example, free-living nematodes of the Rhabditidae (e. g. Sudhaus & Kiontke, 2007) or mites of the Histiostomatidae (e.g. Wirth, 2004).
The cryptospecies phenomenon, which means that closer investigations show that animals once attributed to the same species actually represent several species, can in principle occur in the entire animal kingdom and in plants and fungi too (Shneyer & Kotseruba, 2015). Previously known subspecies are often given their own species status as a result. One example are the two monitor lizard species Varanus niloticus and V. ornatus (e. g. Böhme & Ziegler, 2004).
In this monitor lizard research mainly ecological differences to V. niloticus have been studied. As one of the results, V. ornatus does not have a diapause in summer, which is a distinct difference to V. niloticus (Böhme & Ziegler, 2004). As an unusual phenomenon, a case of parthenogenesis was even observed in V. ornatus, but not in V. niloticus (Hennessy, 2010) so far. However, morphological differences between these two monitor lizards were known even before, for example relating to aspects of the dorsal drawing. But the authors named above were able to provide evidence that these morphological differences do not occur gradually, as orgininally assumed, but rather distinctly.
Another example of two sibling species (the most simple form of cryptic groups) that have been identified as different species by molecular biological studies are Homo sapiens and H. neanderthalensis (e.g. Prüfer et al., 2014). Originally it was assumed that H. neanderthalensis was a subspecies of H. sapiens. This is for example supported by the proven cultural exchange between the two species and the great morphological similarity. In the meantime, however, morphological findings such as the morphology of the nasal duct of the Neanderthal man have also supported the genetic findings (Márquez et al., 2014). However, very recent studies show that Neanderthal genetics have entered the lines of H. sapiens (Hajdinjak er al., 2021). As a result, both forms have crossed and produced fertile offspring. It remains to be seen whether this will possibly dismiss the concept of two species again.
Since the aim of all studies of cryptic species complexes is to find distinctive differences in the areas of morphology, ecology or barcoding (or all approaches together) that distinguish one species from all others, ultimately clearly definable, very closely related species remain in case of successful studies.
If the cryptic organisms are members of an organism-socialization, such as parasites and their hosts, the idea that a proven host specificity can be an indicator for a certain species of a cryptic complex is obvious. In fact, Wirth et al. (2016) for example postulated a host specificity for the phoretic mite Histiostoma piceae and its hosts, the bark beetles Ips typographus and I. cembrae. Nevertheless, relationships between associated species are usually not studied extensively enough to be able to unequivocally identify certain species on the basis of for example their hosts (Wirth, 2004).
Since cryptic species represent nevertheless separate species despite their extraordinary similarity, they are subject to the species concepts. As a result, they form different niches and can therefore appear sympatric in the same living space (e. g. McBride et al., 2009). This makes it difficult for biodiversity researchers and systematics to investigate the real numbers of species in such habitats.
If, instead, cryptic species are not sympatric, but distributed in adjacent areas, this can for example indicate that an allopatric species formation has either not been completed for a long time or is even still in the process of speciation (e. g. Gollmann, 1984).
Animal species that have different developmental stages can appear cryptic, i.e. being morphologically confusingly similar, with regard to all these developmental stages, such as for example certain phoretic free-living nematodes, which then additionally have to be studied ecologically or genetically (e. g. Derycke et al. 2008).
Other species can hardly be distinguished morphologically with regard to a certain developmental stage, which is particularly common, but differ distinctly in other developmental stages, which are more difficult to find. Very similar looking lepidopteran caterpillars of sibling species (e. g. Scheffers et al. 2012) can be more commonly available than their adults, which might be easier to distinguish.
As a specialist for mites of the family Histiostomatidae (Astigmata, Acariformes) I will in my further argumentation refer to my biodiversity studies on these mites and explain the difficult situation for describers of new species based on several specific histiostomatid species, some being phoretically associated with bark beetles and others associated with different coleopterans from muddy sapropel-habitats around ponds in Berlin/Germany. In connection with these cryptic groups of species, reference should be made to the applied difficulties in connection with biodiversity research. I am referring to the fact that, for a variety of reasons, often only a certain juvenile stage (deutonymph) is used for species descriptions (e. g. Klimov & Khaustov, 2018 B), although cryptic species can occur sympatricly in the same habitat and in many cases not be sufficiently differentiated from one another on the basis of just this one stage.
In Histiostomatidae as in most Astigmata taxa, the deutonymph (in older publications hypopus) represents the phoront, being adapted morphologically and behaviorally in getting dispersed by insects or other arthropods. This instar has no functional mouth, possesses a ventral suckerplate to attach to its carriers and a thicker sclerotization against dehydration. The deutonymph is often collected together with its phoretic host. Bark beetle traps are for example a common source, where dead deutonymphs still on their hosts come from and are subsequently forwarded to acarologists, who then are of course unable to create a mite culture in order to have also adult instars available for species descriptions (e. g. Klimov & Khaustov, 2018 B) and other taxonomic purposes. This paper shall clarify, why it is instead necessary for a clear species determination to have the deutonymph and additionally at least adults available.
In this publication two cryptic species complexes from the taxon Histiostomatidae (Astigmata) are presented as result of my original scientific work. On the one hand morphologically very similar representatives of the Histiostoma piceae-group, which are originally associated with bark beetles (Scolytinae), on the other hand similar looking representatives, which are bound to insects in the area of the banks of ponds with digested sludge (sapropel). It needs to be emphasized in that context that those herewith introduced two cryptic clades are phylogenetically not closer related to each other.
The presented bark beetle mites (chapter 1 in results) can only be distinguished morphologically by very gradual characteristics, in terms of phoretic deutonymphs as well as in terms of adults. However, there is a tendency towards host specificity (e.g. Scheucher, 1957), which is why there could be a permanent spatial separation of the species despite common occurrence in the same region.
The mites from the sapropel in the area of the pond banks (chapter 2 in results) are presented on the basis of a certain area in Berlin (Germany), where they appeared sympatric. Unlike the bark beetle mites, they are morphologically clearly distinguishable with regard to the adults, but have morphologically very similar deutonymphs, which essentially only differ from one another in degrees.
Based on the representatives of two different cryptic species groups presented in this work, it should be shown that a sufficient range of morphological features for systematic and taxonomic differentiation and characterization of species can only be available if at least two developmental stages of a population can be studied. It is also pointed out that high-resolution optical methods can uncover a possibly systematically relevant variety of morphological features that would otherwise remain hidden. It is suggested that a suspected host specificity cannot always be used to differentiate between very similar species and that cryptic species can be found sympatricly on the same host as well as in the same habitat. The main aim is to show that there is a risk of confusion and a risk of underestimating the existing biodiversity if only the deutonymph is used for taxonomic purposes, just because it is for example easily available, when the host is captured. Nevertheless species descriptions based only on the deutonymphs are unfortunately still surprisingly common.
Due to the lack of sufficient research fundings and a corresponding decrease of experienced specialists, trends to remarkably simplify determinations and species descriptions are about to manifest themselves. Non specialists or less experienced acarologists increasingly try to recognize or describe new species based on the availability of deutonymphs only, because these phoronts are often easily accessible as bycatch of entomological material. It is mistakenly assumed that faster procedures could accelerate the level of scientific knowledge about the biodiversity of astigmatid mites (Wirth, 2004).
Material and Methods
Chapter 1 is an illustration of the current state of my research about a cryptic bark beetle-associated group of species. Problems and questions are additionally shown both on the basis of existing, in part own, literature. Chapter 2 is about four species of Histiostomatidae that were recorded from an old gavelpit area in the urban Berlin forest Grunewald, named „Im Jagen 86“, located 52° 29′ N, 13° 14′ E. This chapter focuses specifically on Histiostoma maritimum, collected between 2002 and 2012 (and also between 1999 and 2000 during my diploma thesis). Besides H. maritimum three other species were found in the same area and habitat: Histiostoma palustre, collected once via deutonymphs from a beetle of Genus Cercyon in 2002 and reared in culture over about two years on moist decomposing potato pieces, Histiostoma litorale, isolated as adults from sapropel mud once in 2002 and Histiostoma n. sp., reared only one generation long from adults to adults in 2019, inside sapropel-mud samples with moss growth and moist decomposing potato pieces.
Mites of H. maritimum were collected as deutonymphs on the beetles Heterocerus fenestratus (rarer on Heterocerus fusculus) and Elaphrus cupreus from sapropel around two ponds in the named area. After different experiments, mites developed successfully on beetle cadavers on 1.5 % water agar in Petri dishes (diameter 5 cm) at room temperature (ca 20°C, summer 2002). Three cultures (one cadaver of C. elaphrus and twice each time two cadavers of H. fenestratus) were observed over a period of about three weeks (additionally small pieces of beef heart were added to all these cultures to maintain suitable food sources). Adult mites were stored in 80 % ethanol for about 5 days and then critical point dried for SEM studies. Photos were taken by an analogous medium size camera via a Philips SEM 515 and later developed. Still unpublished copies from 2002 were scanned in a high 600 dpi solution and as tiffs via a CanoScan Lide 2010 in 2021. Restauration and picture quality improvement were performed via Adobe Lightroom. The areal panorama of the former multiple pond area was captured in September 2018 via a Dji Mavic Pro drone at a height between 30 and 50 m and subsequently modified into black and white.
Setal nomenclature follows Griffiths et al. (1990).
They live in eusocial communities, but are not closer related to ants or bees. Termites belong to the cockroaches.
Queen, king and castes
Usually one queen and one king are reproductive and act as heads of the nest. The different work fields of a nest are executed by infertile specimens, which can show very different and specialized body shapes. The diversity of different castes is in phylogenetically „primitive“ taxa lower than in „higher developed“ termite groups.
As example specimens of a deadwood species from Italy
This species was found in deadwood of a small forest in Portici (Gulf of Naples, Italy) and might represent the taxon Kalotermitidae. This taxon branches off rather basically in the systematic tree of termites. Nest work can be taken over by nymphs of later alates.
deadwood-termites from Italy, Youtube: copyrights Stefan F. Wirth, April 2020
How is wood-eating possible?
Wood eating termites bear bacteria and protozoans in their digestive tracts, which perform the digestion of cellulose.
Evolution, sister taxon and endosymbionts
Termites (Isoptera) evolved within the cockroaches (Blattodea). According to modern systematics (e.g. Beccaloni & Eccleton, 2011) the cockroach taxon Cryptocercidae is the sister-clade of the termites. But there are controversial theories existing.
According to such reconstructions, the last common ancestor of cockroach taxon Cryptocercidae and termites possessed bacterial and protozoan endosymbionts. Molecular data proved that endosymbionts in both groups are closely related to each other. The last common ancestor of both groups showed in case of their indeed sister-group-relation a tendency towards social communities. Cryptocercidae live temporarily in bigger groups together with their offspring.
Subsocial lifestyle in Cryptocercidae
Cockroaches of the Cryptocercidae as putative sister taxon of termites live inside galleries in deadwood and feed on wood fibres. At least one parent and its nymphs live subsocially inside their galleries. Cryptocercidae adults and nymphs groom each other, and parents feed juveniles with wood fragments afer these had passed their anus openings.
According to recent systematic/ phylogenetic reconstructions the Kalotermitidae belong to the basically branching termite groups. Such basic groups of termites still show a low diversity of castes only.
Associates, commensalism and phoresy
Like ants or bees, termites share their nests regularly with associates of other groups of animals,
often mites and nematodes. Some of these organisms use termites as carriers for a transport over bigger distances. details of such associations between insects and mites are not well studied yet. But carrier-passenger-situations with transfer („taxi“-) purposes are called phoresy. Phoresy ist mostly considered as a neutral association between different organisms and is thus interpreted as commensalism. Commensalism is differed from strategies like parasiticm or symbiosis and requires that two organisms in association do not harm or noticeably benefit each other. The term commensalism often includes associations, in which the true context for both organism partners is simply not understood yet.
Not yet mites of the Gamasina (Parasitiformes) were reared in greater numbers out of my Italian termite substrate. They might represent phoretic cohabitants of those termites. Other mite species of different mite groups (Parasitiformes and Acariformes) were only found in smaller numbers and died out too quickly for collections and determinations under my culture conditions, unfortunately already before the beginning of my shootings. seemingly microclimatic conditions had become too unfavorable.
Copyrights Stefan F. Wirth, Berlin 2019 – 2020, all rights reserved
The bee Andrena flavipes is also known as the common sand bee, as this species represents the most common of several regularly present sand bee species in Central Europe.
Aggregations at suitable nesting sites
Bee females create solitary nests, which is unlike to social hymenopterans such as the honey bee Apis mellifera. However huge and from a distance well visible aggregations of nesting A. flavipes specimens can appear. It is said that these aggregations are due to mated females being attracted to similar suitable nesting sites. In fact also a tolerance for conspecifics very close by is required to allow conditions, in which the whole ground seems to consist of bees, flying around and preparing their nests or importing pollen or nectar to feed their larvae. By the way: One nest contains contains about 2-3 brood cells only.
Specific conditions, in which specimens of my footage were found
The bees of my video were filmed between 4-6 April 2020 in the urban park around lake Plötzensee in Berlin. The site for my recordings was an area with forest edge character, interrupted by dry meadows, all at least in the afternoon exposed by the sun (temperatures between 15-20 °C).
Females of Andrena flavipes cleaning their nests, youtube: copyrights Stefan F. Wirth, April 2020
Orientation and nest cleaning behaviors of A. flavipes females, hindlegs as multifunctional organs
Contents of my behavioral documentation is the cleaning of nest hole entrance areas and behavior patterns, which seemingly support the orientation and finding their own nests again in midst of a sandy forest ground covered by fallen leaves.
To be enabled to recognize the entrance of the own nest again, bees perform regularly smaller walking tours around their nests to memorize soil structure and other details, being suitable to characterize this specific nesting site.
The bee’s hindlegs represent important multi-functional organs. They walk on them, collect pollen, which adhere to specific structures on legs III, and they are used to clean the areas in front of the nest openings from dirt, such as smaller stones or wooden particles. As nest entrance areas stay opened during the day, a proper cleaning of the soil around is regularly necessary. The bee performs that work mostly while backward-walking using its hindlegs like shovels to sweep dirt some centimeters away. This behavior is well visible in my footage.
General and short information about mite associations
Andrena flavipes and other soil breeding wild bees are generally also of acarological interest. As presumably all hymenopterans, they have for example associations with phoretic mites, for example mites of the Scutacaridae (such as Imparipes apicola). I so far did not study mites on these bees, but phoresy means that mite instars use the insect as carrier to reach their final sites, in which they develop and reproduce. In case of Imparipes, adults feed on fungi and waste inside the bees brood cells.
Copyrights Stefan F. Wirth, Berlin april 2020, as always: all rights reserved
We recently read a lot about the pandemic consequences of infections with the new corona virus Sars-CoV-2, most are medical issues, hygienic advises and information about political reactions in different countries worldwide. But there is not much known about the biological host reservoir, putative intermediate hosts and how the human infections might be explained. It is a normal lack of information, because the scientific research about topics, being generally new to science, is time costing, especially, when life strategies and the population dynamics of organisms a concerned. Organisms? Viruses are per definitionem not considered organisms, because they lack important aspects, which characterize real life: they cannot reproduce on their own power, they do not have an own metabolism, no ingestion, no excretion. But they are organic and show traces of life by possessing a genome, which might indicate that they evolved from living cells. Viruses represent a diverse group of protein bodies containing nucleic acid, either DNA or RNA.
New corona virus Sars-CoV-2, Wikipedia: CDC/ Alissa Eckert, MS; Dan Higgins, MAM / Public domain
Viruses in general, host specificity, host increase, host change
For reproduction viruses depend on living host cells, which they reprogram by inserting their virus genome into the cell’s genome in order to stimulate the forming of a number of virus copies, all that happening on cost of the host cell’s life. Thus viruses need to be named parasites as they harm their hosts to their own advantage. Different groups of viruses attack different kinds of cells using in detail different methods to enslave their host cells. There are plant viruses, viruses associated with bacteria (named bacteriophages) and animalistic viruses. They all show characters, which are typical for parasite – host – relationships. Parasitic partners of any kind of host – parasite – relationship can be exclusively associated with one host species only (host specificity) or a limited group of systematically closely related hosts, while others can have a wider range of different host species. The latter generally might have evolved out of the former, although also the opposite direction is thinkable. When former host-specific parasites make themselves one or even several further hosts accessible, then this phenomenon is named host-increase (Wirtserweiterung). In case an new host was infested as permanent host, while the former host is given up, then a so called host change (Wirtswechsel) happened. The same term is also used in a different context, namely when a parasite requires in its development a change between different hosts.
Host specificity: A parasite (or an organism with similar life-strategy) is associated with one host only, which requires a specialization and a competition between host evolution and parasite evolution (coevolution). This strategy needs to be separated from generalism, which means that a parasite has a very wide range of not related regular main hosts. Host specificity is more common than generalism. But this also depends on definitions. I herewith define the association with one main host species only as host specificity. But I furthermore consider host specificity also given, when parasite-host relations are specific on a higher taxonomic level, for example, when certain closely related genera of parasites are specialized for certain closely related genera of hosts. This part of my definition has variable borders. In the chapter after next, I describe the parasitic case of the trematode Leucochloridium paradoxum, whose main hosts are represented by different systematically not closer related bird species. A host specificy on the level of birds in general (Aves), then present in only some species with similar food preferences might already need to be named a limited generalism.
Obligatory host change in ticks and lifstyle-change in water mites
Some parasites need several hosts to be enabled to finish their life-cycles. This is another context, in which the German term „Wirtswechsel“ (host change) is used. In that kind of parasite – host – association, the host change is often obligatory, meaning that the parasite cannot survive in the absence of one of the required hosts. The castor bean tick Ixodes ricinus represents a parasite, which needs a host change to successfully go through its full development until adulthood, but there is a wider range of suitable hosts, as intermediate host and as final host. Thus the tick is a generalist with obligatory host change. Water mites (Hydrachnidia) are parasitic as first nymphs (juvenile instar, usually named „larva“) and predators as older nymphs and adults. A host specificity of „larvae“ can appear, but a wider range of host species is common. These mites perform a life style change during their development.
Intermediate host, for example in the parasitic flatworm Leucochloridium paradoxum
An example for a parasite, obligatory requiring a specific intermediate host, is the flatworm Leucochloridium paradoxum („green-banded broodsac“, Trematoda, Platyhelmintes), whose larvae (miracidium) need to infest snails of the genus Succinea. This trematode parasite is host specific for a genus of snails, while there is no specificity for their main hosts. They parasite birds, but infest different bird species, which are not closer related to each other, such as finches, the crow family Corvidae or woodpeckers. Although there is a main host specificity on the very high taxonomic level of Aves, the use of the term (limited) generalism might in this case even be appropriate. Inside the smail’s midgut gland, miracidia (larvae) modify into another larva-form, named cercaria, which invade the liver, where they form so called sporocysts, sac-shaped muscular tubes, which grow through the entire snail host until they reach the snail’s tentacles, which they fill up with their tube-shaped bodies entirely. Lastly the snail is unable to retract her swollen organs. The snail tentacles are now well visible as conspicuous greenish stripes, pulsating permanently. The sporocysts as larval stage of this trematode parasite do even more than only increasing the visibility of the snail for bird predators, which represent the worm’s final host. They additionally manipulate the nervous system of the snail so far that the snail performs an unusual behavior and moves towards very well exposed elevated areas, such as leaves of adjacent plants. Thus the probability to be eaten by birds is remarkably increased.
Host specificity on humans with side-hosts and coevolution with the ancestor line of Homo sapiens: skin mite Sarcoptes scabiei
An interesting example of a host specificity with numerous side-hosts and even an additional host-increase is the skin parasitic mite Sarcoptes scabiei (also named the „seven-year itch“). It was originally exclusively specific for Homo sapiens and accompanied mankind over its entire evolution (e. g. J. R. H. Andrew’s Acarologia, 1983). Systematical relatives of that mite species can only be found within the Great Apes. Originating from the recent Homo sapiens, S. scabiei conquered the human’s domestic animals, such as dogs or bovine animals within long-term periods, in which humans and their domestic animals had shared the same buildings or even rooms. Domestic animals may transfer the mite-parasite subsequently to wild animals. In case main host (humans) and side hosts (domestic animals, wild animals) can supply everything, which the parasite needs for its development without the necessity to leave its host specimen, one might speak about real hosts. In case side hosts cannot supply the necessary basic equipment, they represent either intermediate hosts or dead-end hosts. It can for example be discussed, whether dogs might in fact be dead-end hosts, as the skin disease can harm them under certain conditions to dead.
Host increase due to the globalisation and human economic interests: example honey bee parasite Varroa destructor (mite)
Another example of a former host specificity on a species‘ level with host increase is the mite Varroa destructor (Parasitiformes, Mesostigmata). It was originally specific for the Eastern honey bee Apis cerana. The mite could only switch over to the Western honey bee Apis mellifera due to a human influence: Men transferred A. mellifera for economic reasons to the natural habitats of A. cerana in Eastern Asia, were it got infected by the mite V. destructor. A subsequent transfer of the Western honeybee back home established the mite parasite in Western countries. As A. mellifera colonies are much more harmed by V. destructor than its original host, our honey bee must be considered as an intermediate case between a new host and a dead-end host. Human international traffic enabled this host-increase primarily, although there are areas between Afghanistan and Iraq, where both bee species coexist due to natural distribution. But there is an almost insurmountable (allopatric) desert border between the population of both species of about 360 to 600 kilometers, although there are evidences for bees rarely surmounting this border. Thus a natural mite transfer between closely related bee species might have happened additionally. Species of animals, plants, fungi or bacteria and even viruses, which successfully established new (additional) living spaces are named neobiota or alien species.
Mite Varroa destructor, Wikipedia: The original uploader was Tullius at German Wikipedia. / Public domain
Can viruses as non-living genome possessing lumps be subject of evolution and complex host – parasite relationships?
Can this high complexity of modes of parasite – host – relationships in living organisms also be found in virus – host – relationships, although viruses do not represent living organisms at all according to biological definitions? The answer is yes, because viruses do not only share a genome with living cells, but based on this genome even are subject to the mechanisms of evolution. And evolution was the most important factor in all the mentioned complex parasite – host – interactions.
Parasitism versus mutualism or harming the host or not harming the host
Two different life-strategies with similar mechanisms as organism – to – organism associations
Are there other organism – to – organism relationships, being subject to a similar complexity than found in parasites with their hosts? Yes, a superordinate term for other close associations between different organism species is mutualism. While parasites need to harm their hosts by using them as final living-sources, mutualists are considered to practice a more neutral host contact, which per theoretic definition means that nobody harms anybody. But the assumption of a neutrality is in fact an artificial construct, as in detail it can come out that some of these organism associations represent unrecognized parasite-relationships, while in other cases a benefit for both partners (symbiosis) or for one partner only might be discovered in future studies. At least so called mutualists share as a feature that harmfulness or benefit are not easily noticeable.
Phoresy: taking a ride on a taxi-host as example of mutualistic relationships
An example for a more neutral organism, at least not harming association is called phoresy. It is often performed by nematodes and mites. These tiny organisms take a ride on bigger animals in order to become carried from one habitat to another. This „taxi-association“ is considered being of advantage for the phoretic part and harmless for the carrier (in English also often named host). But there are seeming phoretic interactions known, which based on developing technical scientific standards could be identified as unusual cases of parasitism. An example is a phoretic instar of an astigmatid mite (Astigmata, Acariformes), which as all phoretic instars within this big mite clade has no functional mouth, but sucking structures to fix itself to its host. This specific mite species had evolved a mechanism for opening the host cuticle in order to incorporate blood of its host using these sucking organs. This is unlike the common use of homologous suckers in related mite taxa, where they (as far as known so far) only support the adherence.
Another interesting example of a phoretic mite is Histiostoma blomquisti (Histiostomatidae, Astigmata), which is specifically associated with the red imported fire ant (sometimes referred as RIFA) Solenopsis invicta, which worldwide appears as troublesome neozoon, again a result of human global traffic. I am the scientific describer of that mite, and my research about it’s biology and abundance in ant nests refers to populations in Louisiana (USA). An interesting aspect is that the ant is originally native to Southern America. We lack studies, whether the mite appears in the native habitats of the ant also as its specific cohabitant or whether it originally deals with a wider range of phoretic hosts. We do not even know, whether the mite is at all native to the same area, in which S. invicta had its natural distribution. On one hand, we hypothesise that, but there is also a theoretical option that the mite performed a subsequent host change in areas, for example in the Southern USA, where the ant was accidentally established via sandy ballast substrate of ships as neozoon. It is further more not known, whether the mite – ant – relationship is indeed neutral, at least with no noticeable harming features. I discovered (S. Wirth & J. C. Moser, Acarologia 2010) that mite deutonymphs (= phoretic instar) can attach to active nest queens in such extraordinary high numbers (hundreds of mite specimens) that mobility restrictions for the concerned queens were sometimes visible. On the other hand, my video documentations showed that even completely overcrowded queens could still freely move and, much more important: stayed reproductive. The purpose of the mites inside the fire ant nests is unknown. But generally, mites of the Histiostomatidae can appear as beneficial animals in ant nests. At least according to my findings about the mite Histiostoma bakeri, which is a phoretic associate of the leafcutter ant Atta texana in Southern USA. I discovered these mites improving the hygienic conditions inside specific nest chambers (detritus chambers) due to their fungi and bacteria feeding activities (Wirth & Moser, European Association of Acarologists proceedings, 2008).
I will in different chapters of this article repeatedly refer to examples with phoretic mites of the family Histiostomatidae (Astigmata, Acariformes). As mutualism and parasitism follow similar organism-host association patterns, I will in those chapters not each time mention again that examples with these mites do not concern parasitism, but mutualism. It is by the way no accident that both life-strategies share common features, as there are examples known, which indicate that one strategy can evolve out of the other.
Mite Histiostoma blomquisti Wirth & Moser, 2010 (Histiostomatidae, Astigmata, Acariformes) on queens of ant Solenopsis invicta, Pineville/ Louisiana, copyrights Stefan F. Wirth
Mutualism often used as neutral term for organism associations with unknown effect of both partners to each other.
The copepod (Crustacea) Ommatokoita elongata on Greenland and sleeper sharks
So called mutualistic associations can sometimes represent interactions of unknown benefits or damage regarding both of the associated partners. Another interesting example of such an association with a not yet understood status is the copepod Ommatokoita elongata (Crustacea), which was discovered as specific cohabitant on the Greenland shark (Somniosus microcephalus) and the pacific sleeper shark (Somniosus pacificus). Larvae of the crustacean in their copepodit stadium and adult females attach to the ocular globes of the shark, where they can cause visible tissue damages. They are thus considered being parasites, although alternating hypotheses assume a more neutral mutualistic copepod – shark – association, based on the sometimes high abundance of the crustacean on one shark specimen (B. Berland, Nature, 1961). There are even assumptions about a benefit contributed by the copepode to the sharks: reasearchers say that it might improve the shark’s hunting success by attracting suitable prey with bioluminescence signals.
Shark Somniosus pacificus, Wikipedia: National Oceanic and Atmospheric Administration / Public domain
Greenland shark with copepod Ommatokoita elongata, hardly visible, when the shark turns to show his right eye, Youtube: copyrights The Canadian Press, video by Ben Singer, footage Brynn Devine, Marine institute of Memorial University of Newfoundland
Human parasites with mutualistic features: the mites Demodex folliculorum and D. brevis
Can viruses be compared with some mites, nematodes or copepodes by performing mutualistic virus – host – relationships? A priori it must be stated that they are unable for a neutral relationship with another organism, as they need the destruction of living cells for their own persistence. But indeed there are viruses known, causing no known diseases and thus being named passenger viruses. But first, an example of an organismic example of parasitism without harmfulness will be presented: the mites Demodex folliculorum and Demodex brevis (Trombidiformes, Prostigmata), which appear as so named „face mites“ inside hair follicles of humans, preferring eyebrows and eyelashes, but also other hairy body parts. The abundance in humans is high and grows with a human age. According to Schaller, M. (2004), new born children are free of Demodex, while over 70 years old people are at almost 100 percent infested with the mites. The mite in fact is a parasite and feeds on sebum from the sebaceous glands. Incorporating needed human gland secretions must be named parasitism. Nevertheless mites under normal conditions cause no visible damages nor do they seem to harm their host noticeably.
So called passenger viruses as mutualists with a more or less neutral affect to their human hosts
Such a parasitic relationship might be comparable with so called passenger viruses, which do not harm noticeably, although they destroy living tissue as all viruses do. They can accompany more harmful viruses and even might harm the pathological success of the diseases, caused by these harmful viruses, and for example might slow the disease’s progression. An example is the GB virus C (GBV-C), which was before known as Hepatitis G virus. The virus is common in humans and shows no pathogenic damaging effect. According to an US-study, about 13 percent of probands, whose blood was examined, possessed antibodies against the virus. GBV-C is considered to slow the effects of an HIV disease by negatively effecting the replication of the HI-virus.
Host increase towards systematically not closer related new hosts
Example for a transfer within related host taxa in mites is the bark-beetle-clade within Histiostomatidae (Astigmata), an example for non related side hosts is the mite Histiostoma maritimum (Histiostomatidae, Astigmata)
Do side-hosts or intermediate hosts as results of host increases commonly need to be systematically close relatives of the main host? The answer is no, although parasites are usually better pre-adapted in infesting a host, which shares a maximum of common characters with the main host. Within the mite family Histiostomatidae, there exists a clade of mites being associated with a clade of beetles. I named it bark beetle-clade (e.g. Wirth, phd thesis, 2004). Mites and bark beetles performed a parallel evolution, which required host increases and host changes towards related hosts and subsequent evolutionary adaptations to harmonize with these new hosts, either to become specific for a new host or to deal with a range of host species.
But the transfer of a parasite to new hosts can also happen towards not closely related host species, representing a scenery being based on a common ecological context between main hosts and side hosts. The phoretic mite Histiostoma maritimum for example is host specific for at least two closely related beetle-species of genus Heterocerus (Heteroceridae). But the mite regularly also appears on predatory beetles of genera Elaphrus and Bembidion (Elaphrus cupreus and Bembidion dentellum, Carabidae) (S. Wirth, phd thesis 2004 and subsequent studies). These beetles partly share the same habitats with Heterocerus: sapropel around ponds, being exposed to sunlight and warmth. In my research about the mite H. maritimum, I hypothesised that the phoretic mite instar might switch over to Elaphrus and Bembidion, for example when these predators feed on adult Heterocerus beetles, larvae or cadavers. Although I could regularly find mites in lower abundances over years on the side hosts (collected in the Heterocerus sampling sites), it is unknown, whether the „switch-over“-scenario was a starting event in an evolutionary past to establish the mite to new additional hosts, where they would today survive more or less independently from the original Heterocerus source, or whether the mites regularly need to switch over in the above mentioned situations, and in consequence side hosts with no Heterocerus-contact would thus lack the mite. A possible support for the latter hypothesis are my laboratory findings about the preferred developmental habitat of the mite, which was cadavers of died Heterocerus beetles. In my experiments the mite remained on its Heterocerus– carrier until this died. Mites subsequently developed on the beetle’s cadavers, feeding there on bacteria and fungi (the phenomenon is named necromeny). Mites under laboratory conditions developed also seemingly successfully on E. cupreus– and B.dentellum-cadavers. But I could so far never continue these studies and don’t know, whether or how well mite colonies with having only cadavers of these two side-hosts available would reproduce compared to mites being reared in Heterocerus settings. In case of a strict substrate specialization for Heterocerus cadavers, the side hosts would be dead-end hosts, and permanent reinfections from the original host source would be required to explain the regular mite abundance in Elaphrus and Bembidion.
Histiostoma maritimum, a adult female with conspicuous copulation opening, b both adult genders in dorsal view, c, d copulation opening in dorsal and sideview, SEM, Berlin 2020/ ca. 2002, copyrights Stefan F. Wirth
Assumed transfer of virus SARS-CoV-2 from bat main hosts via a pangolin as intermediate host towards humans:
There is an ecological context between bats and pangolins
The new corona virus SARS-CoV-2 is assumed to be host specific to a group of animals and from there infesting another animal as intermediatehost, from which presumably humans were opened up as new host source. There are researchers interpreting us humans as an dead-end hosts, as unlike in bats human people can be harmed remarkably with the lung disease COVID-19 (corona virus disease 2019), triggered by SARS-CoV-2. As at least from a general statistical point of view a high majority of infested people shows no or only slight symptoms, thus it can up-to-date not be excluded that Homo sapiens is in order to become a fully potential side host, because all a parasite needs in order to „survive“ before all other requirements is the (statistically) surviving of its host.
There is evidence that bats (Chiroptera) represent the main host, thus representing the „natural virus reservoir“, while pangolins (Pholidota) presumably act as intermediate hosts. This main-host-to-intermediate host context is for example reported as putative scenario by Ye Z.-W et al. (Int Biol Sci, 2020), who stated that based on molecular features the bat Rhinolophus affinis (Rhinolophidae, Chiroptera) is hosting a virus most similar to SARS-CoV-2 differing from all other known corona viruses (Similarity 96.2 %, nucleotide homology). The pangolin species Manis javanica was identified to carry formerly unknown CoV genomes, being according to the same authors with 85-92 % similar to SARS-CoV-2 (nucleotide sequence homology).
Bat Rhinolophus affinis as known reservoir of a virus most similar to Sars-CoV-2. Wiki commons: Naturalis Biodiversity Center
Pangolins and Chiroptera (bats and megabats, this taxon subsequently sometimes refereed as „bats“) are systematically not closer related to each other. Pangolins (Pholidota) are considered to represent the sister taxon of the clade Carnivora. Chiroptera were reconstructed as sister taxon to the clade Euungulata (containing animals such as horses, cattle or whales). But both, Chiroptera and Pholidota, can be connected by an ecological context. Pangolins (Pholidota) are species, which are either adapted to live preferably on the ground, or to spent most of their time on trees. Both types are specialised ant and termite feeders, which use cavities on the ground or inside trees as hideaways. They additionally give birth to their offspring inside these burrows and subsequently use to stay there with their young for a while. Such cavities can accidentally be the same time aggregation and resting places for bats, excluding megabats, which use to rest during daytime on exposed areas on trees. Manis javanica has a semi-arboricol life-style, spending time in trees and on the ground. This pangolin uses different resting cavities, either subterranean burrows or tree cavities.
Chinese pangolin Manis pentadactyla, a ground living species, Wikipedia: nachbarnebenan / Public domain, Zoo Leipzig, Tou Feng
Pangolin Manis javanica as known host of a virus similar to virus SARS -CoV-2. Wikipedia: creative commons Piekfrosch / CC BY-SA
Chiroptera and Pangolins are in South Eastern counties often subject to hunting, as both for example play a role in the traditional Chinese medicine. Thus a virus transfer to humans via main host or via the putative intermediate host is assumed to have happened on animal markets (in the province Wuhan in China).
Which indications point to animal hosts as original source of virus SARS -CoV-2 ?
The scientists Andersen et. al (2020) explain there was no virus-engineering instead of a natural evolution
But which proofs exist that animal hosts sources such as Chiroptera and pangolins are involved in the transfer of the virus SARS -CoV-2 to humans? The lack of general knowledge is still fundament for conspiracy theories, such as an artificial creation of the new corona virus in laboratories with biological warfare purposes.
K.G. Andersen et al. („The proximal origin of SARS-CoV-2“, Nature Medicine, 2020) concluded based on their molecular research that the genetic template for specific spike proteins forming structures, which the virus body possesses on its outside for holding on and penetrating into the host cells, showed evidence for a natural evolution and not for an engineering. They argue with the strong efficiency of the spikes at binding human cells, which makes an engineering implausible and evolution based on natural selection highly probable. The authors additionally examined the overall molecular structure of the backbone of SARS-CoV-2. Backbone can be explained as the „skeleton spine“ of a macromolecule as a continuous row of covalent bond atoms. This overall backbone structure of the new corona virus is according to the authors similar to viruses, which were isolated from Chiroptera and pangolins and dissimilar to other corona viruses, which are already known to science.
Spikes (here in red) in Sars-CoV-2 hold on and penetrate into host cells, Wikipedia: CDC/ Alissa Eckert, MS; Dan Higgins, MAM / Public domain
Can a host increase happen more or less spontaneously with a subsequent enormous success (as for example in virus SARS-CoV-2)?
And: Can the complexity of adaptations to a main host decide for the option of a host increase?
An example for a tendency to spontaneous temporary host changes is mite Histiostoma piceae (Histiostomatidae, Astigmata)
Is it imaginable that a host change or a host increase happens spontaneously and subsequently having such a remarkable impact to the new host, as it is recently ongoing with the SARS-CoV-2 pandemic? Host specificity, host changes and parasitism or mutualism in general are result of evolution. The most common case of evolutionary changes in organisms or viruses is a slow process of stepwise modifications being based on mutations and natural selection.
But it needs also to be stated that as more complex the pattern of characters is (genome, morphology, behavior, function-morphology, reproduction biology etc.), which binds a parasite or mutualist to a specific host, as more evolutionary steps are necessary to perform a host change and as longer an exposure to mutation and selection would need to take place. However it is alternatively possible that a host specificity is only based on a few, but important features. Slighter ecological pressures focusing towards these features might then theoretically allow rather fast host changes.
As an example with a putatively reduced complexity of host adaptations I herewith introduce the phoretic mite Histiostoms piceae (Astigmata, Histiostomatidae), which I repeatedly studied and reared under laboratory conditions. The scientific describer of this species (Scheucher, 1957) discovered a strict host specificity to the bark beetle Ips typographus. According to my and her research, the mite has along the geographic distribution of that bark beetle a high abundance, beetles without the mite are rare. In 2016 I discovered H. piceae being additionally associated with Ips cembrae as a second regular host. I cembrae represents the sibling species of I. typographus (Wirth, Weis, Pernek, Sumarski List, 2016). Exceptions are smaller bark beetle species, which regularly burrow their galleries into those of I. typographus or I. cembrae. It is unknown, whether these small bark beetles as cohabitants of I. typographus carry the mite temporarily or regularly. But the former might be confirmed by the following interesting phenomenon in the mite H. piceae:
In case of very high numbers of mites inside bark beetle galleries and a relatively low numbers of corresponding Ips species, the phoretic instar of the mite attaches under natural field conditions all available arthropods inside or adjacent to the galleries of the main hosts, including bigger mite species, different beetle species or – as already mentioned – smaller bark beetle species (for example my studies in the area of the city Tyumen, Siberia, Russia, 2015-2016). This indiscriminateness for specific hosts under certain conditions might indicate that the substrate specificity of the mite H. piceae is more developed than the phoretic specificity for the host insect itself as a carrier . In such a case, I would generally expect that a host change or a host increase might faster happen in future evolutionary steps than in mite species, which are strictly choosy for their specific host carrier. In H. piceae the tolerance for a variety of carriers (unlike the specificity for substrate conditions) might in a future evolution even succeed as pre-adaptation, which under suitable circumstances might spontaneously allow a regular transfer to new hosts. A second important step towards a real host increase would require that the mite becomes able to stay permanently on its new host. In the H. piceae context the evolution of a tolerance for different substrate conditions might once become an important selective factor in may be opening up new permanent host-associations.
Temporary side hosts, as described in the above explained observations, would represent nothing then dead-end hosts, as they are unable to carry the phoretic mite to suitable habitats for its development. But under favorable circumstances, a former dead-end host might even become a new permanent host.
Histiostoma piceae, a adult female in side view, b in dorsal view, c mouthparts and digitis fixus, d adult male in dorsal view, e in ventral view, Berlin 2020/ ca. 2002, copyrights Stefan F. Wirth
Phoretic instar of Histiostoma piceae, ventral view, lightmicroscope with dig contrast, Tyumen (Siberia, Russia), 2016, copyrights Stefan F. Wirth
Two possible ways of virus transfer from bats to humans according to Andersen et al. (Nature Medicine, 2020)
Did the virus evolution towards the recent state happened prior to a first human infection, namely inside animal main host populations, or did it happen afterwards inside human populations?
As there is not yet much known about the presumed host specificity of the virus SARS-CoV-2, Andersen et al. (Nature Medicine, 2020) reconstructed based on their up-to-date knowledge two possible ways of a virus transfer from bats to humans and finally to the recent pandemic situation in the world:
The virus might have evolved its recent human-pathogenic features within the main host populations of bats. Natural selection must have been the corresponding major driving force. The relevant adaptations are represented by the above mentioned two molecular characters of the spike proteins in SARS-CoV-2 (receptor-binding domain for host cell binding and cleavage sites for an opening up of the virus). Under such circumstances the authors expect that the infection of humans could have happened with an immediate effect, leading at once into the pandemic situation of today. An intermediate host would in this option be not obligatory. A direct transfer from bats to humans might be imaginable.
The second option is based on findings that corona viruses in pangolins possess similar receptor-binding domains (RBD) as in the human SARS-CoV-2 version. Thus the authors reconstruct a version according to which a non or less pathogenic form of the new corona virus was via pangolins transferred to humans and circulated there for an unknown period of time. Even further possible intermediate hosts, such as ferrets or civets, are considered to have been involved in that scenario. During its time inside human populations the virus would have developed its recent features due to evolution and finally was able to be spread explosively between human populations on a pandemic level.
A higher probability for one of the two scenarios can according to the up-to-date knowledge not be assumed
I am not sure, whether the authors take under consideration with their second option that pangolins might even represent a main host and whether bats would not necessarily be involved in the animal-human transfer of the virus. But according to Ye Z.-W. et al. (Int Biol Sci, 2020) the context between bats, pangolins and humans was stated: „We cannot exclude the possibility that pangolin is one of the intermediate animal hosts of SARS-CoV-2“. But whether the pangolin is intermediate host or main host would at this point not effect the general conclusion of each of the two scenarios. The virus was either pre-adapted regarding efficient spike protein characters and then infested human populations rapidly or was transferred to humans via an animal host and subsequently evolved its key-features for a pandemic „success“ within human populations. Although the authors have up-to-date no indications allowing a preference for one of the scenarios, they point out that the potential of new SARS-CoV-2 outbreaks after the extinction of the recent human pandemic would be much higher in case of the scenario one, as the pathogenic virus would under these conditions survive in the animal main host populations.
I would as addition to scenario two suggest to test a modified hypothetic scenario, in which the non pathogenic ancestral version of the virus did not only circulate between human populations until it reached its pandemic key-features, but even circulated between humans and animal hosts forth and back for a longer time. This would according to my understanding of evolution improve the probability of a stepwise evolution of important key-features.
Special and unusual features of main hosts can improve the diversity within their parasites, important conditions for subsequent host changes: a very efficient immune system in bats pushes the evolution of their viruses
Chiroptera (bats and megabats) are not only known as putative main hosts for SARS-CoV-2, but also for Mers, Sars, Marburg and ebola viruses. Scientists did a research about the question, whether there are specific features existing, which explain, why Chiroptera are favorable hosts for viruses with a seemingly potential for epidemic and pandemic effects in human populations.
C. E. Brook et al. (eLife, 2020) discovered an unusual efficient immune system in Chiroptera, which they think protects these hosts from harmful diseases by their virus parasites. This bat immune system is considered being the evolutionary driving force for the variety of viruses and their relatively fast modifications, as they would need to compete with immune system responses by regularly evolving new adaptive features.
The authors discovered that the antiviral messenger substance interferone-alpha is released in most mammals as a response to the detection of viral genetic material inside body cells. Whereas they found Chiroptera releasing this messenger substance permanently. This would according to the scientists enhance the virus defense in bats and might explain that the above named viruses do not trigger noticeable diseases in their main host recervoir.
I would resume that such conditions might support the scenario one of Andersen et al. (Nature Medicine, 2020), according to which viral key features to infest humans had evolved prior inside the animal host populations. Regular new virus modifications as result of the competition between these viruses and their bat-host immune responses might support the randomness of the development of features, which as pre-adaptations could support a relatively fast host change. Even when I generally prefer scenarios of stepwise adaptations of organisms to new conditions, a higher probability of the availability of suitable pre-adaptations might at least accelerate evolutionary proceedings.
Longtime parasite – host – relationships, a dead-end for the parasite?
Are relationships between organisms over longer time periods of advantage or disadvantage for parasitic or mutualistic passengers? A longtime host specificity of a parasite (or mutualist) requires a strict specialisation, which means complex morphological, ecological and behavioral adaptations.
According to the acarologists P. B. Klimov & B. Oconnor (Systematic Biology, 2013) long-term specialisations could impede the flexibility of such organisms to react to environmental changes via evolutionary adjustments. Thus parasites with long-term relationships to the same hosts might be endangered to reach a dead-end. They would die out. A possible way out from such a disastrous end can be a re-evolution of the parasite back to its ancestral free living conditions, a situation prior to the evolution of its parasitic host specificity. But Dollo’s law states that a complex trait cannot re-evolve again. Thus long-term parasitism could according to the law not other than leading into a dead end. Nevertheless the authors could present an impressive example as proof to the contrary: based on their complex research about house dust mites, the acarologists reconstructed that these mites were originally parasites of warm blooded animals and subsequently evolved into free living associates of mammals, as which they are of medical relevance due to the remarkable allergic reactions in humans.
I think that the access of this paper does contain enough general biological aspects to ask, whether the dead-end scenario of long-term parasite relationships might also concern viruses, which don’t have an option for a free living existence, as they don’t live at all and are unable to perform independent strategies. At least might this long-term scenario support the findings of C. E. Brook et al. (eLife, 2020) that only unusual and regularly changing features of a long-term host might trigger regular corresponding responses by the parasite, another option to prevent a parasite from a dead-end due to a long-term host relation. This might explain, why certain viruses often parasite bats and successfully persist there, while other suitable hosts lack the very efficient immune system of bats and thus cannot host a specialized virus permanently. Regarding SARS-CoV-2 such theories might indicate that the virus would finally move towards dead-ends in humans and other host species, but might permanently survive in chiropterans. It’s a statement only being worth of consideration, in case of scenario one of Andersen et al. (Nature Medicine, 2020). And only in case, it would come out that the virus adapts well to humans, which would require a much reduced harmfulness, as parasites cannot survive by killing their hosts. In case of a dead-end host due to high mortality rates instead of a normal host increase, aspects of a long-term relationship with such a host don’t need to be discussed, as a shorter temporary outbreak and no beginning of a long-term relationship at all would result out of it. One needs additionally to consider that viruses as non living organic bodies with genome and with an unusual ability for fast modifications might often not fit into biological models based on living organisms.
House dust mite Dermatophagoides pteronyssinus. Wikipedia creative commons: Gilles San Martin from Namur, Belgium / CC BY-SA
Host specificity must be differed from generalism. Known host-parasite specializations include a complexity of strategies. And even different kinds of hosts must be named, such as main host, side-host, intermediate host or dead-end host. Evolutionary steps such as host increase, host change or temporary hosts can appear. Parasitism and mutualism differ from each other as life-strategies, but share common features as association between different organisms: host specificity follows similar rules, an indication that both life-modes can evolve out of each other. The human globalization sometimes supports the spreading of parasites or their hosts over the world, host changes or host increases can thus be performed including organisms, which would under normal conditions get no contact to each other.
Viruses do not represent living organisms, but protein lumps with a genome and depend on living host cells for their reproduction and „survival“. like in living organisms, also viruses underlay the mechanisms of natural selection and evolution. Viral parasite – host – relationships show general similarities with features in living organisms, including options for a host change or host increase, the use of intermediate hosts or a kind of mutualism (passenger viruses). There is evidence that the main host reservoir of SARS-CoV-2 are Chiroptera, while pangolins (and other mammals) might represent intermediate hosts. Humans are either dead-end hosts (preferred by most authors) or result of a successful host increase. Researchers could not yet decide, whether features to infest humans in a pandemic context evolved prior to the transfer to humans inside animal main host populations or whether a harmless version changed to humans and in their populations evolved its pandemic potential. A major drive motor for a long-term successful relationship with bats is the unusual immune system in chiropterans.
Copyrights Dr. Stefan F. Wirth (phd), all rights reserved, excluding photos labeled as creative common content from Wikipedia sources. Berlin, 2 April 2020
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B. Berland (1961): Copepod Ommatokoita elongata (Grant) in the eyes of the Greenland Shark – a possible cause of mutual dependence. In: Nature, 191, S. 829–830. Cara E. Brook, M. Boots, K. Chandran, A. P. Dobson, C. Drosten, A. L. Graham, B. T. Grenfell, M. A. Müller, M. Ng, L-F. Wang, A. v. Leeuwen (2020): Accelerated viral dynamics in bat cell lines, with implications for zoonotic ermergence,eLife; 9:e48401.g W
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They look without magnification more like very motile and fast running ants or very tiny grasshoppers than like arachnids. But they indeed represent relatives of the web spiders and scorpions: Schizomida, a clade of whip scorpions. They are the sister taxon of Thelyphonida, the rather well known „big whip scorpions“, which are often kept as pets in terraria around the world. Schizomida are only rarely filmed in a higher resolution quality, which is due to their small size and their almost invisibility due to their semi-transparent cuticle and their very fast way of walking or even jumping. They are additionally difficult to be filmed as they strictly avoid all lights and tend to dry out quickly, when they cannot hide themselves by time in a slightly moist substrate.
Closeups of behaviors of a Schizomid species from a greenhouse in Germany. Copyrights Stefan F. Wirth
Schizomida in Greenhouses
Schizomids represent mostly tropical or subtropical organisms. But some species are regularly dispersed into greenhouses around the world. The filmed species might be Stenochrus portoricensis, but was not systematically studied in detail so far. As all known species, which appear in greenhouses, also S. portoricensis reproduces (apart from their original habitats) parthenogenetically with females producing females without mating procedures (thelytoky). I never found males so far.
S. portoricensis: native to subtropical Zones
The specimens, which I kept since months in a small terrarium, were collected in autumn 2016 at the famous fun and wellness bath „Tropical Islands“ South of Berlin. There they are a natural part of the world’s biggest indoor rainforest. The species S. portoricensis is originally native to Florida, Mexico, Cuba, Nicaragua, Porto Rico and other localities in similar tropical zones. These microscopical tiny organisms are predators and do not harm human beings at all. According to the available organisms in a suitable size in my terrarium, they might feed on the numerous collembolans and/or mites. Especially mites of the Gamasina appear in greater numbers in my substrate, which represents the original substrate from the greenhouse. I enriched this substrate regularly by smaller pieces of fruits or vegetables to stimulate the growth of microorganisms. I keep them at room temperature (about 20°C) and with not too much moisture. I do not know, whether they reproduced within these months, but the specimens of my recent video footage represent all sub-adults.
Film set and topic locomotion
Focus of my film is to present the different ways of locomotion, cleaning behaviors and burrowing activities of these fascinating animals. During the filming procedure, I used two cold-light-lamps for a suitable illumination and an ILCE-6300 (internal 4K mode), connected to a stereomicroscope and a lightmicroscope (with uplight).
Berlin December 2019/ March 2017, Copyrights Stefan F. Wirth
Inca terns live along the South American Pacific coast and breed along rocky coastlines of Peru and North Chile. They can be easily identified by their grey plumages, their distinctly red beaks and feeds as well by their conspicious white feather curls on the bases of their beaks.
Geographic distribution and life-strategy aspects of Larosterna inca
Larosterna inca breeds inside rocky walls of coastlines either inside rocky cavities or in old nesting holes of other seabird species. Its hunting ground is the Humboldt Current, which is famous for its cold temperature, but also its enormous fish wealth. To increase its chances for fishing success, the Inca tern might follow sea lions, cormorants and whales and is then hunting fishes, which were flushed up by these bigger sea animals. They also follow fisher boats to catch some rests of their fishery.
According to phylogenetic reconstructions L. inca, which represents the only recent species of its genus, branches off in the Animalia tree within the monophyletic clade of terns. Based on DNA sequences E. S. Bridge, A. W. Jones and A. J. Baker reconstructed in their 2005 paper (Molecular phylogenetics and evolution) a sister-clade relationship between Larosterna and species of the taxa Sterna, Thalasseus and Chlidonias (mitochondrial DNA was used to reconstruct the tern phylogeny).
Terns themselves seem representing an own clade (Sternidae), being for example based on characters of behavioral pattern, and are considered as a sister taxon of gulls (Laridae).
Filming conditions and filming locality
My footage was recorded in the Zoo Berlin, where terns together with other sea birds inhabit a for tourists accessible free-flight enclosure. There I captured scenes about the diving and „fishing“ behavior (specimens fished repeatedly wooden sticks) as well as their plumage cleaning activities on shore and their conspicuous plumage cleaning behaviors via extended bathing trips inside areas of low water. Size of my entire video is 4K. But parts of the scenes were originally recorded in Full HD to enable a better slow motion effect based on 100 frames per second. Such footage was subsequently digitally magnified into the 4K size to fit in the entire video project.
All behavioral activities are at first presented in a slow motion (ca. three to four times slowlier than original speed), then in the much faster original speed.
Plumage cleaning is part of the hygienic behaviors of birds. Feathers can only stay in full function, thermoregulation and flying, when dirt and parasites are removed regularly. Typical plumage parasites are represented by feather mites (no phylogenetic clade), which consist of taxa of the Astigmata (Acariformes) and of taxa of the Dermanyssoidea (Parasitiformes). Feather lice represent a subclade of the (Phthiraptera = lice), named Mallophaga. The monophyletic situation of Mallophaga is seemingly doubtful.
Plumage cleaning and hunting behavior of Larosterna inca, video (4K9, copyrights Stefan F. Wirth. Please like my video on youtube too.
Putative reasons for plumage cleaning behaviors
I couldn’t research sufficient information about specific plumage parasites of Larosterna inca. There is indication that terns generally are relatively free of predators and parasites. Seemingly, plumage parasites of this particular species are still a more or less open research field. But the existence of a regular and visibly careful plumage cleaning might indicate a sensitiveness for corresponding parasites. L. inca can be according to literature (e.g. W. Pieters et al., Avian Diseases, 2014) fatally infested with the trematode Ichthyocotylurus erraticus.
Copyrights Stefan F. Wirth, Zoo Berlin July/ September 2019
Mites represent arachnids, which means that they share characters with much bigger organisms, such as spiders, skorpions or harvestmen. Their bodies consist of specialized bundles of segments, named tagmata. Two major tagmata are differed from each other in arachnids: prosoma, including legs and mouthparts, and opisthosoma, including for example the digestive and the reproductive systems.
Discussed diphyletic origin of mites
Mites are according to some acarological scientists eventually not longer just mites. The former two clades of mites, Parasitiformes and Acariformes, originally considered as sister taxa, were in some modern systematics reconstructed to be diphyletic. That would mean, there was no commor ancestor, from which only those two clades derived, the two major clades would be polyphyletic with no close relationship between them, each clade is assumed being closely related to different groups of arachnids (e.g. Psedoscorpions and Opiliones). Thus, when I talk about mites, I am talking about the clade Acariformes.
Mites of the Acariformes and body plan
In these Acariformes mites, the arachnid body construction plan was modified into three visible tagmata: gnathosoma (bearing chelicerae and pedipalps as mouthparts), proterosoma (bearing first two leg pairs) and hysterosoma (bearing last two leg pairs and opisthosoma organs).
Male (large morph) of mite Histiostoma feroniarum in dorsal view. Body division in gnathosoma, proterosoma and hysterostoma. Fixation : critical-point-dried, SEM photography, copyrights Stefan F. Wirth
Let’s talk about mouthparts, as they are an important aspect of my systematic and my function.morphological studies. Originally the gnathosoma consists of a pair of scissor-shaped chelicerae to grasp the food particles and of a pair of leg-shaped pedipalps, which mostly have mechano-sensitive and chemo-sensitive functions. But because mites colonized almost all kinds of existing habitats on earth, they extensively were exposed to the mechanisms of evolution. Acariform mites show a high range of variability regarding their morphology and their life strategies.
Mouthparts of Sarcoptiformes
Within the clade Sarcoptiformes, consisting of oribatid mites, Endeostigmata (seemingly paraphyletic) and astigmatid mites, there evolved a tendency towards miniaturization. Mites of the Astigmata are usually much smaller than one mm. Correspondingly the cuticle became thinner and softer, perfect adaptations to a life inside very tiny micro habitats, but at the same time also a limitation, namely towards more or less moist habitats due to the lack of a well developed desiccation protection. They appear inside compost, rotting wood or mammal dung, being even there very specifically adapted into very defined micro climatic conditions. They live in a world of complete darkness, which is why light sensory organs are completely lost or reduced to vestigial structures.
Inside their habitats, astigmatid mites need to reproduce, to develop through different nymphal stages until adulthood and of course to feed. Astigmata are no fluid suckers, but feed on particles, such as bacteria, algae, fungi, thus many Astigmata taxa can be named microorganism feeders.
Life-strategy of mites of the (family) Histiostomatidae
Extinct bark beetle fpssil in amber (collection Hoffeins) with phoretic mite deutonymphs. Fixation with hexamethyldisilazane, stereomicroscopic photography, copyrights Stefan F. Wirth
One of the largest family within the Astigmata clade is the Histiostomatidae, which I use since many years as model for my scientific studies. These mites are scientifically interesting from different points of view. Their ecology is characterized by life styles, which correspond to the life cycle of insects and other arthropods, to which most species have a close association. Most important aspect of these interactions between mites and other arthropods, commonly insects, is a dispersal strategy named „phoresy“. Mites use their „partners“ as carriers from one habitat to another. These habitats can often be the nests of the corresponding arthropods/ insects.
Habitats, in which mites of the Histiostomatidae develop successfully need to be moist and need to contain a sufficiant amount of microorganisms as food source. It is the most conspicuous feature of these mites to possess remarkably modified mouthparts compared to the above described standard equipment of an acariform gnathosoma.
Mouthparts of the Histiostomatidae
Mite Histiostoma sp. (sapropel around ponds, female, Berlin) feeding from a substrate surface inside its original habitat. Videography in 4K, copyrights Stefan F. Wirth
The character conditions of the gnathosoma were one of the reasons, why I at the beginning of my phd thesis in 2000 decided to put my research focus on this mite family, being worldwide in major still unexplored.
The chelicera modified into a dagger-like structure being formed by the fixed part of the former scissor-like organ, named the digitus fixus. There is a variability of shapes of this digitus fius-chelicera-ending within the Histiostomatidae . It can appear „simple-dagger-like, simple formed with a hook-like ending or having cuticular dentations of specific numbers and sizes along the lower edge of the digitus fixus.
As typical for mites of the big clade Astigmata, the pedipalps are reduced in size and almost immovably ventrally and dorsally connected with each other. In Histiostomatidae, the third pedipalp article is additionally distinctly bent sidewards. Their front sides bear more or less complex arrangements of flexible membraneous structures, which can morphologically differ between taxa or even species, thus giving them a systematic relevance. I named these membrane-organs „palparmembrane“ following the nomenclature, introduced by R. Scheucher in 1957. These membranes can be devided into fringes or being lobe-sphaped and can cover the last pedipalp article dorsally and/or ventrally. My histological analysis from 2006 indicated that these membranes are shaped by the enditesof the pedipalpal coxae.
Complex mouthpart apparatus
Thus Histiostomatidae possess a bizarre mouthpart apparatus being unique within the Acariformes and representing an amount of characters, which from the phylogenetc point of view can be reconstructed to have evolved in the stem species of that family (so called apomorphies).
Mouthpart apparatus as multifunctional organ
Mite Histiostoma sp. (male left, female right) feeding from a substrate surface inside its original habitat. Fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth
This gnathosoma is a multifunctional organ with the main function to select specific microorganism particles out of their liquid environments. When observing a histiostomatid mite with a sufficient high magnification walking along on a smooth water agar surface, on which bacteria and fungi growth was stimulated before, then occasionally trails can be seen around the walking mite, indicating that the gnathosoma was hold mostly leaned downwards towards the ground, pushing the microorganism cover along in front of the mite’s body. I interpreted this as an accumulation of food in order to gain more nutrients all at once. In my early papers, I described this as the typical feeding behavior of histiostomatid mites with the membraneous appendages acting like rubber sliders in the meantime. But as newer analyses showed is that such observations do not describe the full equipment of possible applications of the mite’s complex filter-feeding apparatus.
Membraneous structures create an underpressure to incorporate food
Mite Histiostoma ruehmi mouthpart endings with palparmembrane in ventral view. Fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth
More recent experiments with a higher videographic resolution and more suitable light conditions than 10 years ago (through-light and up light or one of them depending on the setting) showed that the palpar membrane structures , which more or less surround the entire fore-part (anterior part) of the gnathosoma can act like suckers: When the mite presses its front end of the mouthparts to the underground, an underpressure can be formed based on these membraneous structures. This seemingly facilitates the incorporation of nutrients in that area.
Note from January 2020: In retrospect, I do not consider it sensible to superficially describe the feeding behavior using the palpar membrane at the edge. A precise videographic analysis of individual images exists and is currently being developed into a scientific paper.
Aspects of the histiostomatid feeding behavior, including using the membranous components at the anterior end of the mouthparts (pedipalps), can partly be seen in the video below.
Mite Histiostoma ruehmi and an undetermined species feeding from a smooth artificial substrate surface and performing an underpressure to incorporate food. Videography, copyrights Stefan F. Wirth
Mite Histiostoma cf feroniarum feeding in its original substrate, fixed with hexamethydisilazane, SEM
copyrights Stefan F. Wirth
Mite Bonomoia opuntiae feeding from the surface of a substrate mount inside its original habitat. Rounded particles might represent yeast bodies. Fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth
In my early postdoc-years, still at the FU Berlin, I performed experiments in order to fix mite activities inside their original substrates by filling such a mite-substrate-setting up with 1,1,1,3,3,3-hexamethyldisilazane and warming the corresponding small experimental dish, until the chemical was vaporized. I then sputtered the conserved setting with gold and studied the details on it via scanning-electron-microscopy. Occasionally, mites were shrinkled or deformed after this procedure, but sometimes they stayed in shape and did seemingly still remain in their last activity positions. I several times could take SEM photos, showing that (well visible only in adult mites due to their size) mite specimens can insert their (distal) chelicerae-endings into bigger heaps of substrate (obviously full of nutrients) and use the entire laterally bent pedipalpal articles, including the connected palparmembranes, to lean it against the substrate surface, either to stabilize the chelicerae movents or even to support the incorporation of nutrients again by forming a slight underpressure, or both.
Mite species Bonomoia opuntiae
Early observations during times of my phd-thesis on the mite Bonomoia opuntiae could show that the mouthpart apparatus of this terrestrial/semiaquatic mite works well also under water or inside a watery juce of decomposing cactus pieces. There even a filter function comparable with a fishing net was hypothesised, but so far was never studied in detail. The very distinct fringes along the palparmembrane lobes in this mite species might support this theory. I also studied the semiaquatic mite Sarraceniopus nipponensis feeding inside watery environments (normally the digestive fluids of Sarracenia pitchers), again never focussing in detail in how excactly the feeding mechanism works.
A putatively new species
The herewith presented video shows behaviors of a female of the putative new species Histiostoma sp. , which I discovered in beginning of 2019 in sapropel around ponds inside an old gravel pit area in the Berlin forest Grunewald. The footage is presented in slow motion. The question was about how motile the whole gnathosoma apparatus in a histiostomatid species can be and what kinds of movements occured. As the settings, which I in early years of my mite studies used for videographic studies, were simplyfied and thus unnatural (smooth agar surfaces), I thought it being necessary and important to capture behaviors in a complexly sculptured habitat, namely surfaces of decomposing potato pieces (on which most histiostomatid species use to develop well).
It was visible, based on the specimens of my video of this species, that histiostomatid mites can be able to lift up their entire gnathosomas on a sometimes even higher position than the levels of the rest of their bodies. Additionally the gnathosoma can be turned to the right and to the left. Up and down as well as sideward movements of the whole feeding apparatus were often performed and represented obviously flexible reactions of the mite to the surface structure of the substrate and to the availability of suitable nutrients. In this context I was also interested in details of the movements of the chelicera tips themselves.
Chelicera endings (digitus fixus)
Although they can be used dagger-like and be accurately inserted into muddy substrate mounts, chelicera tips will also appear in a very fragile and seemingly careful way, when palpating the surface of the substrate underneath. Such chelicera movements are visible in the footage of this video, presented in slow motion (about 25 percent of original speed) and in a digital magnification. I interpret this visible fragility caution of the chelicerae as one option to discover suitable food sources. Other important organs perceive the mite’s environment chemically, modified setae, namely the so called solenidia, which might additionally recognize profitable microorganism sources.
Mite Histiostoma feroniarum feeding from substrate mounts inside its original habitat (A-F). Rounded particles might represent yeast bodies. D = distal chelicera endings (digitus fixus), holding food particles, fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth
Gravel pit area „Im Jagen 86“ in Berlin as biotope
„Im Jagen 86“ is a former gravel pit area in the Berlin urban forest Grunewald. It today represents a dynamic biotope, consisting of different types of habitats: mud around ponds, sand dunes, dry grassland and forest. Since the early 2000th, its habitat composition partly changed remarkably. Out of several (smaller) ponds, only one bigger pond remained. All ponds originally were surrounded by sapropel, a habitat for different interesting organisms, such as beetles of Heterocerus, Elaphrus and Bembidion. The mite Histiostoma maritimum was commonly found phoreticaly on Heterocerus and Elaphrus. I additionally in those early 2000th described the new mite Histiostoma palustre from Hydrophilidae of Cercyon and Coelostoma, living inside the saporopel as well. Today only a few small areas with open sapropel exist. I so far did not look for Histiostoma maritimum again and don’t know, how common it still is. At least Heterocerus beetles are harder to find than in earlier years. I so far did not found Histiostoma palustre again.
Rearing conditions of a putatively new mite species
I collected new mud samples in March 2019 at different areas, but found developing histiostomatid mites in a sample from the edge between mud (sapropel) and mosses. It is a species I never found before there and which might represent a new species. Only females could be morphologically studied. Nymyphal stages (not deutonymphs) are only available as video footage. No males were found. I had added bigger potato pieces to stimulate microorganism growth as mite food into the soil sample (room temperature). After about one month, a few mites (females and proto/tritonymphs) developed on only one of these potato pieces and quickly died out shortly after my filming activities and after I could prepare a few females. I actually try to get them reared again. Due to the low temperatures in March, it is considered that these mites hibernate independently from insects in the substrate. No bigger insects could be found in the substrate, which might be the corresponding carriers. But different dipterans (e.g. Ceratopogonidae) developed, they had no mite deutonymphs after hatching in my sample.
Morphological reconstruction of females and important characters as well as behavioral observations
The females of Histiostoma sp. differ from other females, which I know, by the mosaic of the following characters: body conspicuously elongated with a distinctly big distance between hind ringorgans and anus, digitus fixus almost simple shaped, fringes or ridges on palparmembrane, 6 dorsal humps, unusually big copulation opening. Leg setation not yet studied. One pair of ventral setae hardly visible (not in the drawing). Nymphs were observed during burrowing activities (footage), females are may be also able to. Deutonymphs or males would be useful to decide, whether the species is new. Some species are only described by deutonymphs.
Berlin, March/ June 2019 All copyrights Stefan F. Wirth