biologe

Blog and online journal with editorial content about science, art and nature.

Tag: mites

Teaching: Ich als Naturalist – Me as a naturalist

Bumble bee Bombus sp. in Berlin, copyrights Stefan F. Wirth 2021/2022
Honey bee Apis mellifera in Berlin, copyrights Stefan F. Wirth 2021/2022
Deutonymphs of the microscopically tiny mite Schwiebea cf. eurynymphae (Acaridae, Astigmata) formally attached to beetle Phosphuga atrata under the bark of felled tree trunk of Tilia platyphyllos in urban park Rehberge in Berlin, copyrights Stefan F. Wirth, 2021/2022
Larvae of beetle Oryctes nasicornis from Italy with associated gamasid mites under studio light conditions, copyrights Stefan F. Wirth, Berlin 2016/2022
Land crab Metasesarma obesum under studio conditions, copyrights Stefan F. Wirth, Berlin 2017/2022

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Ich biete Unterricht, Förderkurse, Vorträge und Fortbildungskurse zu den Themen Naturkunde, Naturschutz, Artenvielfalt, Ökologie, Klimaschutz und Evolution an sowie Unterricht oder Vorträge zur Naturfotografie oder der Naturfilmerei. All dies entweder auf Honarbasis oder via Anstellung. Bitte entnehmen Sie weitere Informationen meinem Menüpunkt zum Thema Unterricht und Lehre. Selbstverständlich verfüge ich über Qualifikationsnachweise zu meinen diversen bisherigen Lehrtätigkeiten sowie meine fachliche Kompetenz. Bitte beachten Sie hierzu auch meinen Menüpunkt Curriculum Vitae.

Doch was sind eigentlich meine Themengebiete? Im Folgenden finden Sie interessante Fragestellungen aus meinen Kompetenzbereichen.

Was ist ein Ökosystem? Welche Ökosysteme sind gut untersucht, welche eher nicht? Wie gut kennt man die Artenvielfalt von Mikro-Lebensstätten in Deutschland, und was ist über deren biologische (ökologische) Zusammenhänge bekannt? Was ist denn eigentlich eine Art, was sind denn dann Zwillingsarten, und was versteht man gar unter einem Artenkomplex (kryptische Artengruppe)? Ist das Aussterben von Arten ein normaler Bestandteil der Evolution oder ist das Aussterben einer Art immer zwingend ein alamierender Hinweis auf eine (evtl. menschengemachte) Naturkatastrophe? Wieviele Arten aus allen Organismengruppen weltweit kennen wir, und wieviele in etwa kennen wir noch nicht? Warum kennen wir viele Arten, sogar in Deutschland, noch immer nicht? Wie erkennt man neue Arten, und wie ist eine sogenannte Artbeschreibung aufgebaut? Ist der Mensch eine Tierart, und wo im Stammbaum der Tiere ist er dann anzusiedeln?

Warum sind ein Wald, ein Teich oder eine Wiese Orte für interessante Entdeckungen, und zwar insbesondere auch für Kinder? Was lebt denn da, und wie ist es an seinen Lebensraum angepasst? Was haben unterschiedliche Arten in solchen Lebensräumen eigentlich miteinander zu tun? Und wie beobachtet man Tierverhalten am besten? Wie dokumentiert man es aussagekräftig, um sein Wissen später mit Freunden oder über soziale Netzwerke teilen zu können?

Wie kommt es zum sogenannten Global Warming, der globalen Klimaerwärmung? Wie können wir sie nachweisen? Warum ist sie zu einem beträchtlichen Teil menschengemacht? Und welche Auswirkungen haben Klimaerwärmung und die Ausbeutung natürlicher Ressourcen (Energiespeicher, Rohstoffe, wie zum Beispiel Tropenholz) für die Zukunft der Menschheit und die Artenvielfalt auf unserer Erde. Welche Auswege erhofft man sich? Woran wird derzeit gearbeitet?

Was benötigt man zur Naturfotografie, was, wenn man zusätzlich oder alternativ auch noch auf gutem Niveau filmen möchte? Was ist grundsätzlich wichtiger: Das Equipment oder das Bild, das zuvor im Kopf des Fotografen oder Filmers entsteht? Muss taugliches Equipment immer ultra-teuer sein? Welche Software eignet sich am besten zum Editieren? Was genügt dabei den Ansprüchen von Anfängern, was benötigen Fortgeschrittene und Profis? Wie filme oder fotografiere ich draußen in der Natur? Wie hole ich stattdessen die Natur in mein Fotostudio und inszeniere sie dort so, dass es aussieht, als habe man im Freien gearbeitet?

Dies sind alles mögliche Themen, die in meinem Unterricht, meinen Kursen oder Vorträgen vertieft werden können. Beliebige weitere Fragestellungen aus den Bereichen Naturkunde, Biologie, Ökologie und Evolution arbeite ich gerne für Sie aus.

I offer lessons, remedial courses, lectures and advanced training courses on the subjects of natural history, nature conservation, biodiversity, ecology, climate protection and evolution, as well as lessons or lectures on nature photography or nature filming. All this either on a fee basis or via employment. Please see my menu item on the subject of teaching for further information. Of course, I have proofs of qualifications for my various previous teaching activities as well as my professional competence. Please also note my menu item Curriculum Vitae. 

But what are my topics? In the following you will find interesting questions from my areas of competence:

What is an ecosystem? Which ecosystems have been well studied and which not? How well do you know the biodiversity of micro habitats in Germany and what is known about their biological (ecological) relationships? What is actually a species, what are sibling species, and what is meant by a species complex (cryptic species group)? Is the extinction of species a normal part of evolution or is the extinction of a species always an alarming indicator of a (possibly human-made) natural disaster? How many species from all groups of organisms worldwide do we know, and roughly how many do we not yet know? Why do we still not know many species, even in Germany? How do we recognize new species and how is a so-called species description structured? Are humans an animal species, and if so, where do they belong in the animal tree?

Why are a forest, a pond or a meadow places for interesting discoveries, especially for children? What lives there and how is it adapted to its habitat? What do different species actually have to do with each other in such habitats? And what is the best way to observe animal behavior? How can you document it meaningfully so that you can later share your knowledge with friends or via social networks? 

How does the global warming come about? How can we prove its existence? Why is it largely human-made? And what are the effects of global warming and the exploitation of natural resources (energy stores, raw materials such as tropical wood) on the future of humanity and biodiversity on our planet? What exits to avoid emergency situations are we hoping for? What are scientists currently working on to ensure a healthy human future? 

What do we need for nature photography, what if we also want to film at a good level in addition or as an alternative? What is fundamentally more important: the equipment or the image that is created in the head of the photographer or filmmaker? Does suitable equipment always have to be ultra-expensive? Which software is best for editing? What meets the requirements of beginners, what do advanced and professionals need? How do we film or take photos outdoors in nature? Instead, how do we bring nature into our photo studio and stage it there in such a way that it looks as if we were working outdoors? 

These are all possible topics that can be deepened in my teaching, courses or lectures. I would be happy to work out any other questions from the fields of natural history, biology, ecology and evolution for you. 



all copyrights Stefan F. Wirth Berlin 2022

Mites, Biodiversity, evolution, species extinction, new species

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.

© Stefan F. Wirth, Berlin 2022

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..."

Two different forms of cryptic species-complexes in mites of the Histiostomatidae (Astigmata) from bank mud and bark beetle-galleries and their significance for applied biodiversity research

Biologe ISSN 2750-4158

Stefan F. Wirth, acarologist, freelancer, Berlin, Germany

Citation: WIRTH S. F. (2021): Two different forms of cryptic species-complexes in mites of the Histiostomatidae (Astigmata) from bank mud and bark beetle-galleries and their significance for applied biodiversity research. Biologe (ed. Stefan F. Wirth), category : original scientific papers volume 1 (2021; 2022) , 1-7. URL: https://biologe.wordpress.com/2021/12/31/two-different-forms-of-cryptic-species-complexes-in-mites-of-the-histiostomatidae-astigmata-from-bank-mud-and-bark-beetle-galleries-and-their-significance-for-applied-biodiversity-research

Abstract

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.


Keywords: cryptic species groups, evolution, biodiversity research, Acariformes, Histiostomatidae, Astigmata, phoresy, Histiostoma piceae, Histiostoma Scheucherae, Histiostoma piceae, Histiostoma ulmi, Histiostoma palustre, Histiostoma litorale, male morphology, SEM, Histiostoma maritimum, Scolytinae, Carabidae, sapropel


Introduction


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).



Results:

Seiten: 1 2 3 4 5 6 7

Ant Lasius fuliginosus: Winged alates and insect/mite nest cohabitants

Ants usually reproduce via mating flights. So also the black wood ant Lasius fuliginosus, whose nest I discovered in the Berlin urban park „Rehberge“, where it was (and is) located in the depth under a spruce tree stump. I filmed them under favorable (climatic) for mating flights.

In some cases workers needed to force them to stay out. This behavior is well visible in my film.

Do ants live alone inside their nests? No, not at all. Numerous non-ant-organisms are adapted in living with them, using all kinds of tricks to be not attacked by the ant workers. A known example is the beetle Amphiotis marginata. Where do they reproduce, where does the offspring lives and develops? Semingly according to science and researcher Prof. B. Hölldobler still partly unknown. I also cannot contribute much. But: An undetermined larva of the same family, Nitidulidae, was found to be active under fruit bodies of the fungus Trametes versicolor on the nest top, adjacent to a beetle pupa (not known, whether the same species or family). When exposed to the ant trail near the fungus, the nitidulid larva was attacked, but not caught and was seemingly sufficiently defensive without a visible activity, thus may be chemically. The behavior is visible in my footage. The pupa in contrary was caught and carried away by the ant workers.

Numerous other insects, many mite species and nematodes inhabit ant nests. But some might just occasionally get in contact with a „suddenly“ forming ant nest colony, being remnants may be from former conditions, and nevertheless persist the passing ants on their crowded trails. Two species of mites of the Astigmata seemed to belong to that kind of cohabitants.

According to the visible different galleries of bark attacking insects, it is assumed that this was the way, how these mites came to their place on the inside of the (still partly well intact being) bark of the spruce stump, may be indicating that it was not too long ago felled down. Most conspicuous were the irregular shaped galleries of the bark beetle Dryocoetes autographus (Scolytinae), partly still equipped with remnants of dead beetle individuals. As typical secondary bark infesting insect, this beetle prefers harmed or dead wood. And might have been there already before or while the ant nest grew.

Film about ant Lasius fuliginosus in a park in Berlin with nest cohabitants, 2020, all copyrights Stefan F. Wirth

The mites were found free or attached to a wood insect on: the inside of the bark, which the ants use as major trail to access their main nest in the depth, means much ant fluctuation. But there was no clear indication for a direct phoretic interaction with the ants, because species one was only found as one deutonymph attached to another insect host, species 2 in different instars, rather no further ant-transport necessary.

Species one: a deutonymph on an undetermined beetle larva, later isolated and filmed via light microscope in motion. Seemingly belonging to Acaridae. Species two: two or three free deutonymphs and two tritonymphs close to bark beetle remnants, being Histiostomatidae, seemingly Histiostoma dryocoeti Scheucher, 1957. Due to the filming activities and the few mites, no slides were prepared, determinations are based on light microscopic footage and photos of living (thus not cleared) individuals. Scheucher’s description is bad and lacks juveniles, males and the female’s dorsum, the deutonymph’s drawing is almost sketch-like. Already for that reason, I determine my mites as Histiostoma cf. dryocoeti. being determined basically based on the deutonymph. Also because I could not see all important deutonymphal details, but the shape (smurf-house-roof-shaped, dorsal view) of the proterosoma, the entire body proportions, the pattern of dorsal setae (as far as visible on the photos) and especially their shape (like typically for bark-beetle-histiostomatids more or less directed forewards, but distinctly shorter than normally) as well as the leg shapes (distal end similar to Scheucher’s drawings) and the rather small rounded suckerplate and the short palposoma (ending with or before dorsal proterosoma) fit more or less to her description. The seemingly corresponding tritonymphs were not described by her, but according to my research fit at least to bark-beetle-species (dorsal structures). But paired posterior elongations are visible and might (not necessarily) indicate similar structures in adult females too, while Scheucher doesn’t show the female dorsum at all and just writes „no special features existing“ about it. Thus the tritonymphal morphology forces me to name the species with „cf.“ even more. The tritonymphal mouthparts (palparmembrane) seemingly show lateral elongations (almost fitting to Scheucher’s description).

I filmed on one day directly on the nest, mites were recorded the same day and subsequent days (end May, beginning June)at home using a light microscope with upper light and a stereo microscope.

Berlin, December 2020, copyrights Stefan F. Wirth

Ant cricket and beetle Amphotis marginata in a nest of Lasius fuliginosus

The ant Lasius fuliginosus builts its nests into wooden environments, for example tree stumps. In the depth it is shaped by a carton-like substance, produced by the ants and with a „domesticated“ fungus involved. When ant workers leave the nests on trails, marked with pheromones, they might seek for food (mostly aphid secretions) in distances up to 30 meters. In the area around the nest, so called foraging trails are especially busy, as different kinds of foraging substances need to be carried in, in order to feed the fungus, in order to create new cartonage and in order to feed queen, nest mates and offspring.

Such a foraging trail is of course a very attractive place for invaders (non ant species) to either capture some food from the workers on their ways into the nest, or even to attach to these workers to get a ride inside the nest too, interesting for brood parasites for example, but also for all kinds of organisms, which prefer nest micro climatic conditions and want to be additionally secured or at least tolerated by the ants. All these organisms, such as insects, mites or nematodes, even pseudoscorpions, need to have specific adaptations in order to be not attacked by the ants.

Film about nest cohabitants of Lasius fuliginosus, Berlin 2020, copyrights Stefan F. Wirth

Three examples are presented in my video. The ant cricket Myrmecophilus acervorum is a common inhabitant of different ant species. Here I found it while „walking in row and order with the ants“. That unusual tiny cricket is assumed to be able to adopt the „smell“ of a nest, which is why ant workers accept it around them. I discovered the specimen of my footage in a later afternoon (around 18:00 in May 2020) directly on top of the tree stump, in which the nest is hidden (in the depth). There it directly followed ants within their foraging walk to the nest entrances. It was directly walking with them in a row and seemed to imitate additionally antennae movements of ants. It after a while left the row of ants (unharmed and without getting a special attention) and went into a hideaway on the side of the tree stump. Generally, there is not much known about the biology of this cricket. There is evidence that it feeds on food and even brood of the ants.

Another ant trail invader is the tiny beetle Amphiotis marginata (Nitidulidae), which performs behaviors, which make its stay inside foraging trails of ants (seemingly associated with Lasius fuliginosus only) even necessary: Hölldobler & Kwapich (2017) had studied this beetle and its behaviors in detail. According to their findings, the beetle shows a complex behavior to beg for food from passing-by antworkers. Movements of its antennae are an important part of such a contact and might in the optimal case lead to a response by the ant to antennate back to the beetle’s head, and subsequently the beetle might be fed as if it were an ant conspecific. The authors describe that a beetle is not always successful. In the best case, hectic ants on their way home might simply oversee the invader (kleptoparasite), in the worst case, they might detect it as a stranger and would then attack it. For protection, the beetle is able to closely adhere to the ground with its claws, while the side edges of its elytrae are shaped downward to the ground. This way, ants are unable to lift such a beetle up and would continue their ways after a while. Hölldobler and Kwapich also mention that they observed cases, in which ants were nevertheless able to lift detected beetles up and then cut their legs off, which means the end of the beetles adventurous life. The beetle specimen in my footage found a bad position aside to an ant path, which was such busy that it was overseen and even unable to approach single workers to beg for food. The authors above found some indications that the beetle’s larvae might develop inside ant nests.

As an acarologist, I am of course interested in mites, which are associated with ant nests. I in detail was involved in research about non-native ants: in the USA (Lousiana) I did research about the leafcutter ant Atta texana and the red imported fire ant Solenopsis invicta, all in cooperation with John C. Moser. I even described a new species of astigmatid mites from S. invicta. I also did some unpublished research on native ants and thus know that also Lasius fuliginosus possesses greater numbers of mite-associates (Parasitiformes and Acariformes). As an example given in this video, we see a rather big mite of the Mesostigmata (Parasitiformes), which I could not determine closer based on my footage. Mesostigmata generally can appear as phoretic organisms (feeding for example on nematodes or mites inside the ant nests, but being carried by ant workers there), they can also invade by themselves and might appear as brood or kleptoparasites. The mite in my footage walked directly on the ant trail without being harmed. It might be like the ant cricket able to adopt ant nest scents to be protected.

Berlin, Plötzensee/ Rehberge, May 2020, copyrights Stefan F. Wirth

Systematics and biology of termites and about their phoretic associations

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

Host specificy, host change and intermediate hosts in different organisms – with special reference to viruses and Sars-CoV-2

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.

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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.

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Parasite Leucochloridium paradoxum, sporocysts inside the tentacles of a snail of genus Succinea, Wikipedia: Thomas Hahmann / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

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.

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Mite Sarcoptes scabiei (Astigmata, Acariformes), Wikipedia: Kalumet / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

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.

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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.

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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.

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Mite Demodex folliculorum, Wikipedia: Information |Description=Demodex folliculorum |Source|Date=2009-09-08 08:34 (UTC) |Author=: http://www.legart.ru/demodex

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.

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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).

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Megabat Cynopterus brachyotis as example for a species native to Southeast Asia, Wikipedia: Anton 17 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

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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.

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Chinese pangolin Manis pentadactyla, a ground living species, Wikipedia: nachbarnebenan / Public domain, Zoo Leipzig, Tou Feng

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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.

SARS-CoV-2_without_background

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

hpiceaeimage0498photoshop

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.

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House dust mite Dermatophagoides pteronyssinus. Wikipedia creative commons: Gilles San Martin from Namur, Belgium / CC BY-SA

Summary

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

References:

J. R. H. Andrew’s (1983): the origin and evolution of host associations of Sarcoptes scabiei and the subfamily Sarcoptinae Murray. Acarologia XXIV, fasc. 1.

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

Pavel B. Klimov, Barry OConnor, Is Permanent Parasitism Reversible? (2013): —Critical Evidence from Early Evolution of House Dust Mites, Systematic Biology, Volume 62, Issue 3, Pages 411–423.

Kristian G. Andersen, Andrew Rambaut, W. Ian Lipkin, Edward C. Holmes, Robert F. Garry (2020): The proximal origin of SARS-CoV-2. Nature Medicine.
Martin Schaller: Demodex-Follikulitis. In: Gerd Plewig, Peter Kaudewitz, Christian A. Sander (Hrsg.): Fortschritte der praktischen Dermatologie und Venerologie 2004. Vorträge und Dia-Klinik der 19. Fortbildungswoche 2004. Fortbildungswoche für Praktische Dermatologie und Venerologie e.V. c/o Klinik und Poliklinik für Dermatologie und Allergologie LMU München in Verbindung mit dem Berufsverband der Deutschen Dermatologen e.V. (= Fortschritte der praktischen Dermatologie und Venerologie. 19). Springer Berlin, Berlin 2005, ISBN 3-540-21055-5, S. 273–276.

Wirth S. (2004): Phylogeny, biology and character transformations of the Histiostomatidae (Acari, Astigmata). phd thesis. Internet Publikation FU Berlin, http://www.diss.fu-berlin.de/2004/312.

Wirth, S. & Moser, J.C. (2008): Interactions of histiostomatid mites (Astigmata) and leafcutting ants. In: M. Bertrand, S. Kreiter, K.D. McCoy, A. Migeon, M. Navajas, M.-S. Tixier, L. Vial (Eds.), Integrative Acarology. Proceedings of the 6th Congress of the European Association of Acarologists: 378-384; EURAAC 2008, Montpellier, France.

Wirth S. & Moser J. C. (2010): Histiostoma blomquisti N. SP. (Acari: Histiostomatidae) A phoretic mite of the Red Imported Fire Ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Acarologia 50(3): 357-371.

Ye ZW, Yuan S, Yuen KS, Fung SY, Chan CP, Jin DY (2020): Zoonotic origins of human coronaviruses. Int J Biol Sci ; 16(10):1686-1697. doi:10.7150/ijbs.45472.

Zhang W., Chaloner K, Tillmann HL, Williams CF, Stapleton JT (2006): „Effect of Early and Late GB Virus C Viraemia on Survival of HIV-infected Individuals: A Meta-analysis“. HIV Med. 7 (3): 173–180.

https://www.sciencedaily.com/releases/2020/03/200317175442.htm

Mite Histiostoma sp., putatively new species, from mud around ponds (Berlin) and its morphology

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

Oribatida mites: Fast runners and slow crawlers

Microhabitats often consist of a complexity of organism species. Under suitable conditions, samples can be kept „alive“ for months and even for years by regularly adding moisture and organic tissue, in case of my sample of this footage: patato pieces.

 

 

Mites of the Oribatida and their different ways of locomotion. Copyrights: Stefan F. Wirth, Berlin April 2019. Please give the video a like on youtube too.

 

Soil samples from island Norderney

 

This soil sample was collected in summer 2018 on the North Sea island Usedom during my participation at the „Geo Tag der Natur“. It contained several specimens of the predatory chilopode Lithobius sp. and pieces of rotting wood, moss and forestground, everything collected under rotting treetrunks and tree branches. The samples additionally contained the carabid beetle Pterosticus cf. niger and ants of genus Lasius. Samples were collected in a small forest area with wetland aspects. The soil quality was rather moist.

 

Astigmatid mites

 

I later added potato pieces and regularly some water droplets to the sample with still living big arthropods/ insects. After some weeks, specimens of the astigmatid mite Acodyledon cf. schmitzi developed on dryer areas of the potato pieces. These mites were presumably phoretic associates of the carabid beetles. They died out after several months, after the sample had dried out a little bit and may be due to changes of the room temperature during winter time.

 

Oribatida

 

Now, almost a year later, the micro habitat is inhabited by mites of the Oribatida in greater numbers of specimens of at least three species: Nothrus sp. (genus not yet clarified), Nothrus palustris (already found for the first time shortly after the sample collection) and a species of Phthiracarida.

 

Locomotion and biodiversity

 

Purpose of the short film is to show different organisms, cultured after about a year in this sample: mites, nematodes, collembolans and microorganisms, fungae and bacteria. Of the bigger arthropods/insects, only one Lithobius species survived until now.  Also the diversity of ways of locomotion in different oribatid species is emphasized: There are slow crawlers (Nothrus) and fast runners (Phthiracarida).

 

Berlin, April 2019, Copyrights Stefan F. Wirth

Mite Histiostoma sachsi (Astigmata): Juvenile dispersal instar deutonymph and its orientation behavior

Some animals live in environments, where there is (almost) no light available. It makes no sense to see in the dark, but it is important for a specimen to know, where it actually is, where it is going to, whether there is enough food and what the conspecifics are doing. Predators need to be recognized in time, and a sexual partner must be found. There is also need for an efficient communication between specimens of a species. How can all this be performed by mites of the Astigmata, which usually live inside decomposing soil habitats in a more or less permanent darkness?

 

Olfactory sense organs in mites of the Histiostomatidae

 

Histiostoma sachsi (Histiostomatidae, Astigmata) is such a mite, living inside cow dung or compost. It might have a rudimentary ability for a light perception, but has not visible or functional eyes. It cannot produce any sounds. It can only feel and smell. Seemingly very limited abilities, but the contrary is fact: Due to evolution this mite is perfectly adapted to its life-style. It can feel objects by touching on them using its body setation (= body hairs). And it smells by means of very specialized body hairs, which are called solenidia and appear in different types, shapes and functions. These mites don’t smell on the level of us humans, which would be very insufficient. If at all, it should be compared with a dog. I am always fascinated when seeing blind dogs and how perfectly they can interact with their environment, despite their handicap. That’s may be how the efficiency of olfactory perception abilities of such a mite must be imagined. They do not only perceive scent particles from other animals, plants and soil components. Even olfactory signals from their conspecifics will be correctly and differentiatedly interpreted. And that not only marginally.  Olfactory signals represent indeed the major mode of their intraspecific communication.

 

Chemical communication of mites of the Histiostomatidae

 

Communication always requires contributions from both sides, a signal and an answer. These mites smell the signal of a conspecific using their solenidia, and they answer by the secretion of biochemical components. For these purposes, they possess a huge and complex gland system located on the upperside of their backs. Volatile excretions aggregate inside a big and rounded reservoir and finally leak to the outside via a pore, called oilgland opening. These gland systems are located symmetrically on both sides, each with one reservoir and one pore.

The meaning of the sent volatile message simply depends on the composition of the correspondingbiochemical components. Even diffferent stereochemical configurations of the same molecule can have different meanings. Citral for instance is a major component and has in different stereoisomers different functions. Such cummunicative volatile signals are usually named pheromones. And mites of the Histiostomatidae can indeed produce different kinds of pheromnes via the same gland system. Aggregation pheromones inform specimens about a suitable place to stay together with their conspecifics, for example due to a sufficient amount of food resources. Alarm pheromones solicit mites nearby to flee from an unpleasant situation. Sexual pheromones attract adult partners to each other in order to perform the mating procedure. But the gland secretions can even more. As allomones, they communicate with specimens of other species. They function as defenses against predators or other dangerous cohabitants.

 

Deutonymphs need to find a carrier for dispersal

 

Another form of communicative interspecific interactions is performed by a specific juvenile instar, the deutonymph. It looks morphologically quite different from all other instars (heteromorphic situation), does not need or possess a functional mouth, has a thicker cuticle as protection against drying out and a complex sucker organ on its underside in order to attach itself to an insect or another bigger arthropod. Deutonymphs of the astigmatid mites search for bigger carrier-arthropods to get carried from one habitat to another (dispersal strategy  is calledphoresy). While doing so, they again use their specifically modified leg setation (hairs) on the first pairs of legs to perceive scents for the detection of a suitable and passing by carrier. Basically it is still unknown, whether the term „communication“ is indeed appropriate in this context as we don’t know yet about a mutual interaction between deutonymphs and their carriers, before the phoretic ride begins.

 

 

Olfactory orientation of the deutonymph of Histiostoma sachsi, copyrights Stefan F. Wirth, February 2019.

 

Specific way of walking in deutonymphs

 

In detail, different kinds of behaviors can be observed in deutonymphs, when searching a carrier. The detailed behavioral patterns in this context can slightly differ between even closer related species. Deutonymphs of Histiostoma sachsi as all deutonymphs show a characteristic mode of walking, in which especially the first pair of legs plays an important role. During each step, performed by four pairs of legs, the first legs are lifted up much higher than all other hind legs. While doing so, they slightly tremble up and down. A behavior that mostly supports a better basic orientation inside a „jungle-„micro-landscape, being filled up with soil particles and decomposing plant tissues. But what H. sachsi deutonymphs additionally need in order to find their carriers is repeatedly to rest between the walking activities. Thus the first legs, which normally are still walking legs, are made free and that way available for the perception of carrier-scent-components only. These  namely are the legs that bear the highest densiy of solenidia.

 

Two different behavioral modes for an efficient orientation towards a carrier

 

Two different modes of resting with olfactory searching activities could be observed: In periodic intervals the deutonymph attached to the ground by using its sucking structures. They were then more or less laying on their entire undersides with only their forebodies slightly lifted up. By alternating moving the first legs up and down, olfactory information could be perceived from all directions without having the own body as a barrier to backwards. To improve its orientation situation, the deutonymph additionally turned on its own axis around, being stabilized by its sucking structures, which are flexible enough to follow these movements. When the deutonymph intended to continue its walk, it first needed to detach from the ground, which happened via muscle contractions that caused an abrupt detachment of the corresponding suckers. But main aim of the deutonymph is to find an elevated place, where the probability of a passing by carrier is especially high and from where a bigger insect (or other arthropod) can easier be ascended. There the second behavioral mode was performed. The deutonymph only fixed the edge of its hind body to the ground, again using the suckers on its underside, which are located close to this edge. This time the entire mite body stood in an upright position. The first legs again „waved“ alternating up and down and could under these especially elevated conditions even perceive scents from bigger distances. By occasionally slightly and alternating turning their upright bodies to both sides, olfactory information could be easier detected from all directions.

 

Carrier of H. sachsi still unknown

 

The frequency of such movements in mites increases typically as closer a suitable carrier approaches. But this was not yet observed or documented for Histiostoma sachsi. Its carrier inside the compost substrate is still unknown, which is why I so far could’t perform corresponding experiments. The species‘ describer, Scheucher (1957), found her mite specimens in cow dung and also didn’t identify the corresponding carriers there.

The observations presented in my video are part of my research project about morphologies and behaviors of deutonymphs in the Histiostomatidae.

 

Berlin, February 2019. All copyrights Stefan F. Wirth.