Mite Histiostoma palustre (Histiostomatidae, Astigmata), a mite species with two different male types

Current state of knowledge

Habitat and summary of general biology

I discovered the mite Histiostoma palustre in 2000 (and reared it at least until 2001) in the Berlin gravelpit area „Im Jagen 86“ at about 52°29’18.7″N 13°14’28.2″E and published the description in 2002 (2003). It is phoretically associated with at least two Hydrophilidae beetle species in bank mud (sapropel) around (in times of the sampling several) ponds. The phoretic juvenile instar deutonymph attaches its host insect to be carried that way to a new suitable habitat.

SEM photograph of ventral side of the deutonymph of Histiostoma palustre. © Stefan F. Wirth

SEM photograph of ventral side of Histiostoma palustre deutonymph as negative version, emphasizing single sicking structures and shapes of hind legs, © Stefan F Wirth

Phoretic hosts and attachment site

I in those times determined two host beetles as belonging to the genera Coelostoma and Cercyon. In laboratory host choice tests, in which deutonymphs in a culture had the choice between three different potential host species, there was a significant preference for those Hydrophilidae beetles, while another offered beetle species sympatrically living the same habitat was almost not at all attractive for the phoresy instar. But the choice test was performed as a smaller side project only and offered not more than a host tendency, as for example not a representative variety of insect species from the same natural field habitat of the mite was involved in these choice tests. But indications were at least clear enough that a host specificy (on a higher taxonomic level) of H. palustre can be stated. Mites preferred according to these tests a specific area for attachment on their hosts, which was the dorsal head area.

Two different male types and the difference between polymorphism und polyphenism

The mite showed under laboratory conditions a male diphenism with highly modified gripping organs or normal legs2. While the modified leg can appear on both sides or only on the left or the right side.

„Polymorphism“ is used internationally as the overriding term for such a phenomenon. Here, following the teaching of my former research group at the FU Berlin, I distinguished between a purely genetically determined expression of distinctly deviating morphs and the determination of these morphs by the presence of certain environmental factors. In the latter case we are talking about polyphenism. Of course, genetics also play a certain role here additionally.

Studies with cultures grown at different temperatures suggested that males with modified legs 2 appeared significantly more frequently at higher temperatures than at lower temperatures.

Temperatures: 30-32 °C (measured in summer inside the culture dishes at room temperature) and 20°C (climate cabinet, temperature inside and outside the cultures almost equal). Experimental approaches and total numbers of males counted: 10 cultures with lower (don’t remember exactly) numbers of developing mite stages per each of the two different temperatures. n=237 males in total at low temperature, n=729 males in total at high temperature. The number of modified males grew significantly from 18% (20°C) to 45% (30°C), while normal males decreased significantly from 82% to 55%.

Therefore I called the mechanism for the formation of two morphs diphenism. These studies were also a besides project and the amount of data would need to be even bigger according to higher level statistical requirements.

SEM photos of a male morph with modified legs 2, © Stefan F Wirth

Detailed SEM view to a male with legs 2 on both sides modified into gripping organs, perspective almost from the front side. © Stefan F Wirth

About the function of the modified male legs

I could observe in the mite cultures in which H. palustre thrived very well on decomposing potato pieces at about 20°C room temperature that the modified legs of the heteromorphic males used as prehensile organs played a role in intraspecific competition for female mating partners. Here several males, with and without gripping organs, were usually wedged together in veritable clusters around female tritonymphs or adult females. This was because the fighting happened more or less in a slow motion speed with apparent longer lulls in between. During the fights, the legs of the opponents were seized with the prehensile organ and the competitor was slowly pulled away from the coveted female.

Less is known about which selective pressure would favor the morph with gripping organ

Males with normally developed legs were at least seemingly in my observations clearly at a disadvantage here, since their second legs in particular could be easily grasped and they were hardly capable of defense and counterattacks. Nevertheless, random counts at that time did not provide any clear indication that heteromorphic males were possibly found significantly more frequently in the final mating position. The same applies to expectations regarding an unequal sex ratio in favor of males. Instead, males and females appeared to be almost evenly distributed in random evaluations. Additionally males with modified legs on both sides and with only one modified leg on the right and the left were in randomly counted cultures seemingly equally distributed.

Still many questions unanswered about the biology of H. palustre

It was unfortunately not tested at all, whether females mated by heteromorphic males and those mated by homomorphic ones had different reproduction successes. In connection with this biologically highly interesting mite species, many questions about its life strategies could not be examined deep enough during times of my PhD thesis. There was no time for this, since my research at the time was geared towards systematic comparative studies of numerous species. Unfortunately, the species could so far not be found again in its habitat „Im Jagen 86“ – at least not by the means of substrate samplings with only accidental Hydrophilidae inside – until today so that further studies were not yet carried out. This seeming lack of the species‚ presence in its former habitat is probably due to ecological changes in this area, which originally had several ponds, from which now only one remained.

A normal leg 2 of H. palustre compared with a modified leg indicating homolog leg articles and corresponding setation.

What makes this male diphenism interesting from the evolutionary point of view

Two distinct morphs within the same sex of a species is the result of evolution. It does at first not matter, whether it is a dimorphism or a diphenism. A fundamental question, which cannot be answered at this time, is: does the trait of these two morphs indicate that the species is on the way to finally having exclusively only males with prehensile organs, and is the species even on the verge of becoming the to cross the species boundary into a new species? Or is the characteristic of two male types a permanently stabled character, because exactly this has strong selection advantage?

In this context, fossil finds of closely related species (in amber) would be of interest, but unfortunately these are not yet known. It would also be interesting to compare different populations of this species, which are also not yet available. It furthermore would be of interest to understand, what exactly the advantage of modified males versus non modified males might be. Is it possible that an advantage of the modified-legged males is simply that they copulate more frequently, although smaller datasets have not yet confirmed this? And/or do females mated by modified males produce significantly more offspring?

And in the special context of the knowledge at that time that it is a temperature-dependent diphenism, one could raise the question of whether the species „evolutionally prepared itself“ by developing two male forms to cope better with temperature fluctuations. In view of increasing global warming, this may be of general biological interest.

A similar species from Egypt

A publication about a species with modified legs 2 as in H. palustre

In a conference proceedings contribution Bishlawy, S. E. M. O., and S. F. M. Allam published an article containing the description of a species of Histiostomatidae, which the authors have named Histiostoma egypti ( Proc.2nd Inter.Conf.Ent.Soc.Egypt, vol. 1, pp. 407-420, 2007). This is worth of being mentioned here more detailed in context of a possible close relationship of these species or a convergent evolution. But due to the lack of systematic facts, a decision hypothesis is not yet made. I can just emphasize that one showed me photos of that species on a conference in Cairo (Egypt) in 2003, and my first and superficial interpretation was that it even is Histiostoma palustre.

I have not checked whether the species Histiostoma egypti has been accepted internationally as a new species and is therefore also listed in the Zoological Record, as this is not relevant to the considerations here. It is interesting that a similar species was discovered in Egypt, about which there are some biological observations.

However, I only have a text version without illustrations, which is online published like that and which is why I cannot assess this species systematically/taxonomically on a deeper level. The authors refer to a similarity of their species with Histiostoma palustre including a similar diphenism of the males. I, as I already mentioned above, remember confirming this resemblance at an acarological conference in Cairo in 2003, where the co-author showed me photos of the later H. egypti.

Association with laboratory cultures of entomopathogenic nematodes

According to the authors, the species entered the laboratory with entomopathogenic nematode substrate and is doing well in the nematode cultures. The mite species is called semiaquatic, which quickly dies off at lower humidity. According to the authors, the thriving of the mites is to the detriment of the nematodes, which can die as a result. In this context, the authors mention having observed that the heteromorphic male form appears more frequently when live nematodes are present, while the homomorphic form and also the phoretic deutonymphs predominate when previously present nematodes have died.

My general experiences with histiostomatid mites and free living (phoretic) nematodes

A connection between the development of different mite morphs and the presence or absence of living nematodes never became particularly obvious to me in my studies at the time on species with different male types. Therefore, I have never specifically investigated such a connection and can therefore judge the correctness of such a connection as neither improbable nor very probable.

I can confirm, however, that basically all Histiostomatidae species that I examined always appeared together with nematodes, which were usually free-living, microorganism-eating representatives of the Rhabditidae or Diplogastrinae, which are also phoretic and possibly even were spread by the same hosts as the mites.

In this context, I am aware of the phenomenon that nematodes and mites can either compete with each other for food or reduce each other, for example chemically. In any case, it can often be observed that after some time in a culture vessel in which both animal groups were initially numerous, only the mites or the nematodes thrived in large numbers.

General information about the feeding behavior in Histiostomatidae

According to my recent research, based on frame-by-frame videographic analysis and SEM studies, Histiostomatidae species use their filter-feeding mouthparts to feed on decomposing fungal material that is also bacteria-rich. It is highly probable that the fungi are brought by the mites themselves into their habitat, which seems to happen hyperphoretically via fungal spores. The mites probably also control the growth and partial death of the fungus themselves in the form of their fungicidal gland secretions. Specific studies about the feeding behavior of H. palustre do not exist on a more advanced level. Slides and numerous SEM shots might indicate the transport of spores, but I so far had no time to examine those specimen closer. Such results thus need to be presented at another occasion.

Information about nomenclature used in the 2003 publication and about the citation of this species description

Nomenclature for dorsal/ventral setation of juveniles and adults used in this old species description of mite H. palustre was my own invention and is no longer used by me for practical/systematic reasons of comparison.

The nomenclature I introduced at the time of that species description for the pattern of individual fields that cover the thickening of the cuticle (proterosoma shield) on the anterior dorsal side of the proterosoma is still retained by me to this day. I still consider this characteristic in adults to be systematically relevant.

Cuticular shield of H. palustre stabilizes muscle origins at the dorsal proterosoma, close to the mouthparts, © Stefan F. Wirth

The original species description is cited as a 2001 publication on the Acarologia abstract page and is cited as 2002 publication in the PDF of the article provided by Acarologia as open access publication. In fact it was accepted for publication in 2001 and finally published in 2003. Thus I sometimes cited it as 2003 publication, but 2002 would be a correcter citation too. At least the full species name must be Histiostoma palustre Wirth, 2002.

Link to the original species description:

https://www1.montpellier.inra.fr/CBGP/acarologia/article.php?id=1849

© Stefan F. Wirth 2023, Berlin

Mate guarding of a juvenile female in mites of the Histiostomatidae (Astigmata, Acariformes)

Male of Histiostoma sp. guards a female tritonymph, copyrights Stefan F. Wirth 2005-2022

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A strategy to avoid male competition for females

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Some mites of the Histiostomatidae practice so-called mate guarding of subadult females in order to have an advantage in the intraspecific competition between males for adult females. My SEM image shows a male on top of a female, which is still inside its tritonymphal cuticle. Inside the tritonymphal cuticle, the adult female is already developed and shortly before hatching. Before hatching, the legs of the new instar are folded under the body side. The new second leg on the right side is visible in the SEM, because the weak cuticle of the old leg broke off. This strategy to avoid sexual competition is quite common with Histiostomatidae. Due to insufficient mite material and not longer available clear ecological data, I determine the long haired adults of my old SEM series with caution as Histiostoma sp., it seemingly was found around sap flux on a tree trunk in Berlin. The species is not identical with Seliea pulchrum (= Histiostoma pulchrum), typically known from sap flux. The distance between the male legs 1 and 2 in the photo is about 0.1 mm. These SEM objects were seemingly chemically dried for the scanning electron microscopic procedure. The photos were taken around 2005 with an older SEM at FU Berlin. © Stefan F. Wirth Berlin 2022

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

Mite Histiostoma piceae

The mite Histiostoma piceae Scheucher, 1957 is a member of the mite family Histiostomatidae (Astigmata, Acariformes). Scheucher discovered the mite based on all instars from spruce, infected by the bark beetle Ips typographus. She collected her samples in Regensburg, Höbing (bei Roth) and Harz. Scheucher reared her specimens on potatoes and bran, but describes that her cultures did grow well only to some degree.

According to her findings,  phoretic carrier (hosts) is the bark beetle species Ips typographus, she also found deutonymphs rarely on some staphylinids. She discovered that free living non-deutonymphal stages develop on fresh detritus, while deutonymphs appear only on old detritus („after it was for a longer time removed from the trees“, „wenn der Mulm einige Zeit aus den Bäumen entfernt ist“). I could like Scheucher culture the mites on potato, but a bit better in their original gallery substrate. Under laboratory conditions, they indeed did not rear very well in both kinds of cultures.

I collected H. piceae between 2000 and 2004 once from a wooden log infested by I. typographus in Berlin, then got access to microscopic slides from Europe in the collection of John C. Moser (Louisiana, USA) in 2007 and 2009, then I collected samples from Ips typographus and I. cembrae in Central Croatia (publication Wirth, Weis and Pernek, 2016) and found out that H. piceae is not restricted to I. typographus, but also to its sibling species I. cembrae. I finally collected the mite from I. typographus galleries between 2015 and 2016 in Western-Siberia near the city Tyumen.

I repeatedly observed deutonymphs of H. piceae under natural conditions (bark samples directly after the excursions) to develop in very high numbers, then attaching to all available arthropods nearby, smaller bark beetle species and numerous bigger mites of different groups, such as for example oribatids.

Published recordings of H. piceae from other bark beetles than I. typographus and I. cembrae are doubtful and need to be named Histiostoma cf. piceae. In some cases with I. typographus additionally present, I interpret the mites to have switched from their regular carrier (host) to an adjacent gallery of e.g. another smaller bark beetle species. In other cases, the existence of similar looking species new to science needs to be tested. In cases of determinations by non specialists from bark beetles other than the above mentioned two beetle species, it needs to be assumed that these people could not differ between similar mite species, such as Histiostoma trichophorum Oudemans, 1912, Histiostoma ulmi Scheucher, 1957 or Histiostoma crypturgi Scheucher, 1957.

 

I never before published the full set of SEM and light microscopic photos from these  times (except of my article about host specificity). In this explicite photo publication here on my homepage, I herewith publish SEM-photographs, objects sputtered with gold, which might be not unique to science, but very rare.

Any subsequent research on this mite in Europe is not happening (a few not too relevant findings are published by a former Russian colleague). Reason is that modern science does not understand, especially not in Germany, that fundamental research in applied fields is worth to be funded. It is for example known that deutonymphs of different mite species on bark beetles regularly carry fungus spores (different fungus species, just sticking on the mite’s cuticle), discovered by John C. Moser and confirmed by several of my own publications. This phenomenon is still not closer studied. Fungus transport into bark beetle galleries can influence the micro climate there.

 

 

Male and female of Histiostoma piceae, A venter of male, B dorsum of male, C mouthparts with Digitus fixus, D dorsum of female, E side-frontal view to female; Berlin 2002-2020, copyrights Stefan F. Wirth

 

Deutonymph of Histiostoma piceae in ventral view, collected in Western Siberia, 2015 – 2016, copyrights Stefan F. Wirth

 

Systematics: Histiostoma piceae is according to my phd thesis from 2004 and according to my more recent research findings a member of a clade (monophylum) within Histiostomatidae with most species associated with bark beetles (Scolytinae) or other bark inhabiting coleopterans; these phylogenetic findings are based on morphological characters.

Mite Histiostoma maritimum

The mite Histiostoma maritimum Oudemans 1914 is a member of the mite family Histiostomatidae (Astigmata, Acariformes). Oudemans discovered the mite based on its deutonymph only from a Dutch island. The German acarologist R. Scheucher found the species in 1957 in mud at the riverside of Regnitz and for the first time could rear H. maritimum and was able to redescribe it by its adult stages, especially females look morphologically conspicuous due to a sclerotized cuticula shield around its copulation opening. She reared her specimens on potatoes, mud and bran, but describes that her cultures did not grow well.

Phoretic carrieres (hosts) are beetles of genus Heterocerus, some carabids and according her findings also rarely some staphylinids.

I discovered H. maritimum between 2000 and 2004 repeatedly in sapropel around ponds in an old gravel pit area in Berlin, forest Grunewald, named „im Jagen 86“. They were mainly attached to the beetles Heterocerus fenestratus and Heterocerus fusculus, but could regularly also be found on the carabids Elaphrus cupreus and Bembidion sp.. I could several times rear the mites, like Scheucher almost unsuccessfully on potatoes, but well on cadavers of their carriers. I thus reconstructed a so called necromenic life-strategy for H. maritium. This means that a phoretic stage ascends a carrier, but never leaves, instead it awaits the carrier’s natural dead to develop on its cadaver (published in my phd thesis, online, 2004).

I will not publish my full set of SEM photos from earlier times here. Some photos will be saved for one of my upcoming paper submissions in scientific and peer-reviewed journals. In this photo publication here on my homepage, I at least publish some interesting SEM-photographs, based on objects sputtered with gold and a subsequent critical-point-drying procedure.

Adults of Histiostoma maritimum: A left male, right female, B, C, copulation opening, D dorsal view to female with mouthparts and copulation opening

Systematics: H. maritimum shares morphological characters of deutonymph (setation, apodemes) and adults (mouthpart details, shape of Digitus fixus) with species like Histiostoma feroniarum, H. insulare, H. litorale, H. palustre, H. polypori, H. myrmicarum. This might indicate a separate clade, but according to the old findings in my phd thesis, also a paraphyletic grouping including these species is thinkable.

Copyrights Stefan F. Wirth, 10 June 2020

Complex and modified mouthparts in Histiostomatidae mites

Mites represent arachnids, which means that they share characters with much bigger organisms, such as spiders, skorpions or harvestmen. Their bodies consist of specialized bundles of segments, named tagmata.  Two major tagmata are differed from each other in arachnids: prosoma, including legs and mouthparts, and opisthosoma, including for example the digestive and the reproductive systems.

Discussed diphyletic origin of mites

Mites are according to some acarological scientists eventually not longer just mites. The former two clades of mites, Parasitiformes and Acariformes, originally considered as sister taxa, were in some modern systematics reconstructed to be diphyletic. That would mean, there was no commor ancestor, from which only those two clades derived, the two major clades would be polyphyletic with no close relationship between them, each clade is assumed being closely related to different groups of arachnids (e.g. Psedoscorpions and Opiliones).  Thus, when I talk about mites, I am talking about the clade Acariformes.

Mites of the Acariformes and body plan

In these Acariformes mites, the arachnid body construction plan was modified into three visible tagmata: gnathosoma (bearing chelicerae and pedipalps as mouthparts), proterosoma (bearing first two leg pairs) and hysterosoma (bearing last two leg pairs and opisthosoma organs).

Male (large morph) of mite Histiostoma feroniarum in dorsal view. Body division in gnathosoma, proterosoma and hysterostoma. Fixation : critical-point-dried, SEM photography, copyrights Stefan F. Wirth

Mouthparts

Let’s talk about mouthparts, as they are an important aspect of my systematic and my function.morphological studies. Originally the gnathosoma consists of a pair of scissor-shaped chelicerae to grasp the food particles and of a pair of leg-shaped pedipalps, which mostly have mechano-sensitive and chemo-sensitive functions. But because mites colonized almost all kinds of existing habitats on earth, they extensively were exposed to the mechanisms of evolution. Acariform mites show a high range of variability regarding their morphology and their life strategies.

Mouthparts of Sarcoptiformes

Within the clade Sarcoptiformes, consisting of oribatid mites, Endeostigmata (seemingly paraphyletic) and astigmatid mites, there evolved a tendency towards miniaturization. Mites of the Astigmata are usually much smaller than one mm. Correspondingly the cuticle became thinner and softer, perfect adaptations to a life inside very tiny micro habitats, but at the same time also a limitation, namely towards more or less moist habitats due to the lack of a well developed desiccation protection. They appear inside compost, rotting wood or mammal dung, being even there very specifically adapted into very defined micro climatic conditions. They live in a world of complete darkness, which is why light sensory organs are completely lost or reduced to vestigial structures.

Inside their habitats, astigmatid mites need to reproduce, to develop through different nymphal stages until adulthood and of course to feed. Astigmata are no fluid suckers, but feed on particles, such as bacteria, algae, fungi, thus many Astigmata taxa can be named microorganism feeders.

Life-strategy of mites of the (family) Histiostomatidae

Extinct bark beetle fpssil in amber (collection Hoffeins) with phoretic mite deutonymphs. Fixation with hexamethyldisilazane, stereomicroscopic photography, copyrights Stefan F. Wirth

One of the largest family within the Astigmata clade is the Histiostomatidae, which I use since many years as model for my scientific studies. These mites are scientifically interesting from different points of view. Their ecology is characterized by life styles, which correspond to the life cycle of insects and other arthropods, to which most species have a close association. Most important aspect of these interactions between mites and other arthropods, commonly insects, is a dispersal strategy named „phoresy“. Mites use their „partners“ as carriers from one habitat to another. These habitats can often be the nests of the corresponding arthropods/ insects.

Habitats, in which mites of the Histiostomatidae develop successfully need to be moist and need to contain a sufficiant amount of microorganisms as food source. It is the most conspicuous feature of these mites to possess  remarkably modified mouthparts compared to the above described standard equipment of an acariform gnathosoma.

Mouthparts of the Histiostomatidae

Mite Histiostoma sp. (sapropel around ponds, female, Berlin) feeding from a substrate surface inside its original habitat. Videography in 4K, copyrights Stefan F. Wirth

The character conditions of the gnathosoma were one of the reasons, why I at the beginning of my phd thesis in 2000 decided to put my research focus on this mite family, being worldwide in major still unexplored.

The chelicera modified into a dagger-like structure being formed by the fixed part of the former scissor-like organ, named the digitus fixus. There is a variability of shapes of this digitus fius-chelicera-ending within the Histiostomatidae . It can appear „simple-dagger-like, simple formed with a hook-like ending or having cuticular dentations of specific numbers and sizes along the lower edge of the digitus fixus.

As typical for mites of the big clade Astigmata, the pedipalps are reduced in size and almost immovably ventrally and dorsally connected with each other. In Histiostomatidae, the third pedipalp article is additionally distinctly bent sidewards. Their front sides bear more or less complex arrangements of flexible membraneous structures, which can morphologically differ between taxa or even species, thus giving them a systematic relevance. I named these membrane-organs „palparmembrane“ following the nomenclature, introduced by R. Scheucher in 1957. These membranes can be devided into fringes or being lobe-sphaped and can cover the last pedipalp article dorsally and/or ventrally. My histological analysis from 2006 indicated that these membranes are shaped by the enditesof the pedipalpal coxae.

Complex mouthpart apparatus

Thus Histiostomatidae possess a bizarre mouthpart apparatus being unique within the Acariformes and representing an amount of characters, which from the phylogenetc point of view  can be reconstructed to have evolved in the stem species of that family (so called apomorphies).

Mouthpart apparatus as multifunctional organ

Mite Histiostoma sp. (male left, female right) feeding from a substrate surface inside its original habitat. Fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth

This gnathosoma is a multifunctional organ with the main function to select specific microorganism particles out of their liquid environments. When observing a histiostomatid mite with a sufficient high magnification walking along on a smooth water agar surface, on which bacteria and fungi growth was stimulated before, then occasionally trails can be seen around the walking mite, indicating that the gnathosoma was hold mostly leaned downwards towards the ground, pushing the microorganism cover along in front of the mite’s body. I interpreted this as an accumulation of food in order to gain more nutrients all at once. In my early papers, I described this as the typical feeding behavior of histiostomatid mites with the membraneous appendages acting like rubber sliders in the meantime. But as newer analyses showed is that such observations do not describe the full equipment of possible applications of the mite’s complex filter-feeding apparatus.

Membraneous structures create an underpressure to incorporate food

Mite Histiostoma ruehmi mouthpart endings with palparmembrane in ventral view. Fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth

More recent experiments with a higher videographic resolution and more suitable light conditions than 10 years ago (through-light and up light or one of them depending on the setting) showed that the palpar membrane structures , which more or less surround the entire fore-part (anterior part) of the gnathosoma can act like suckers: When the mite presses its front end of the mouthparts  to the underground, an underpressure can be formed based on these membraneous structures. This seemingly facilitates the incorporation of nutrients in that area.

Note from January 2020: In retrospect, I do not consider it sensible to superficially describe the feeding behavior using the palpar membrane at the edge. A precise videographic analysis of individual images exists and is currently being developed into a scientific paper.

Aspects of the histiostomatid feeding behavior, including using the membranous components at the anterior end of the mouthparts (pedipalps), can partly be seen in the video below.

Mite Histiostoma ruehmi and an undetermined species feeding from a smooth artificial substrate surface and performing an underpressure to incorporate food. Videography, copyrights Stefan F. Wirth

Scanning-electron-microscopic experiments

Mite Histiostoma cf feroniarum feeding in its original substrate, fixed with hexamethydisilazane, SEM

copyrights Stefan F. Wirth

Mite Bonomoia opuntiae feeding from the surface of a substrate mount inside its original habitat. Rounded particles might represent yeast bodies. Fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth

In my early postdoc-years, still at the FU Berlin, I performed experiments in order to fix mite activities inside their original substrates by filling such a mite-substrate-setting up with 1,1,1,3,3,3-hexamethyldisilazane and warming the corresponding small experimental dish, until the chemical was vaporized. I then sputtered the conserved setting with gold and studied the details on it via scanning-electron-microscopy. Occasionally, mites were shrinkled or deformed after this procedure, but sometimes they stayed in shape and did seemingly still remain in their last activity positions. I several times could take SEM photos, showing that (well visible only in adult mites due to their size) mite specimens can insert their (distal) chelicerae-endings into bigger heaps of substrate (obviously full of nutrients) and use the entire laterally bent pedipalpal articles, including the connected palparmembranes, to lean it against the substrate surface, either to stabilize the chelicerae movents or even to support the incorporation of nutrients again by forming a slight underpressure, or both.

Mite species Bonomoia opuntiae

Early observations during times of my phd-thesis on the mite Bonomoia opuntiae could show that the mouthpart apparatus of this terrestrial/semiaquatic mite works well also under water or inside a watery juce of decomposing cactus pieces. There even a filter function comparable with a fishing net was hypothesised, but so far was never studied in detail. The very distinct fringes along the palparmembrane lobes in this mite species might support this theory. I also studied the semiaquatic mite Sarraceniopus nipponensis feeding inside watery environments (normally the digestive fluids of Sarracenia pitchers), again never focussing in detail in how excactly the feeding mechanism works.

A putatively new species

The herewith presented video shows behaviors of  a female of the putative new species Histiostoma sp. , which I discovered in beginning of 2019 in sapropel around ponds inside an old gravel pit area in the Berlin forest Grunewald. The footage is presented in slow motion. The question was about how motile the whole gnathosoma apparatus in a histiostomatid species can be and what kinds of movements occured. As the settings, which I in early years of my mite studies used for videographic studies, were simplyfied and thus unnatural (smooth agar surfaces), I thought it being necessary and important to capture behaviors in a complexly sculptured habitat, namely surfaces of decomposing potato pieces (on which most histiostomatid species use to develop well).

It was visible, based on the specimens of my video of this species, that histiostomatid mites can be able to lift up their entire gnathosomas on a sometimes even higher position than the levels of the rest of their bodies. Additionally the gnathosoma can be turned to the right and to the left. Up and down as well as sideward movements of the whole feeding apparatus were often performed and represented obviously flexible reactions of the mite to the surface structure of the substrate and to the availability of suitable nutrients. In this context I was also interested in details of the movements of the chelicera tips themselves.

Chelicera endings (digitus fixus)

Although they can be used dagger-like and be accurately inserted into muddy substrate mounts, chelicera tips will also appear in a very fragile and seemingly careful way, when palpating the surface of the substrate underneath. Such chelicera movements are visible in the footage of this video, presented in slow motion (about 25 percent of original speed) and in a digital magnification. I interpret this visible fragility caution of the chelicerae as one option to discover suitable food sources. Other important organs perceive the mite’s environment chemically, modified setae, namely the so called solenidia, which might additionally recognize profitable microorganism sources.

Mite Histiostoma feroniarum feeding from substrate mounts inside its original habitat (A-F). Rounded particles might represent yeast bodies. D = distal chelicera endings (digitus fixus), holding food particles, fixation with hexamethyldisilazane, SEM photography, copyrights Stefan F. Wirth

Berlin, September 2019

Copyrights Stefan F. Wirth

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.

 

Eudicella colmanti – Mating behavior of a colorful beetle

Rose chafers represent a group of colorful beetles, which taxonomically belong to the Scarabaeidae and thus are relatives of famous beetles such as Scarabaeus sacer, well known for rolling dung into balls and for being an important symbol for creation and the rising sun in the ancient Egyptian world. Even the stag beetles are more distant relatives of rose chafers.

 

Colorful and active during daytime

 

Unlike some related beetle clades, rose chafers are usually active during the day. This is also indicated by their very colorful bodies. Colors in insects can have different functions, but they usually all are optical signals, which require a visibility in the sun light. Greenish colors are common in rose chafer species and might have optical inner specific signal functions, but also might support an optical camouflage. This would also make sense in the preferred habitats of the adult beetles, which usually feed on softer parts of blossoms and on their pollen. But they also feed on fruits, whereby mostly liquids are incorporated as the chewing mouthparts are not very well developed.

 

Tropical rose chafer Eudicella colmanti during its copulation behavior, 4K videography, copyrights Stefan F. Wirth.

 

Tropical rose chafers from African countries

 

About 3000 species of rose chafers are known, of which most inhabit the tropical zones. The about 20 species of the genus Eudicella are more or less restricted to the African continent.

Eudicella colmanti is native to Gabun, Kamerun and Kongo, thus a species with a main distribution in Central Africa. But E. colmanti is like other species of this genus worldwide often kept in terraria, although species like E. smithi are more common inhabitants of this kind of artificial habitats. They all can be more or less easily reared.

 

Specific flying mode and copulation behavior

 

This is why I was able to study behavioral characters in detail. And rose chafers indeed show interesting behaviors. They for example perform a unique way of flying. It is a specific character of rose chafers (a so called apomorphy) that they fly with closed fore wings, which cannot be opened as in other beetles.

I documented in my video the mating behavior of a beetle couple. Interestingly this was not too difficult, although both genders can, when separated from each other, react to disturbances with a high agility.

 

Almost permanent copulation activities

 

But in the copulatory position, they accepted to be removed from their terrarium to the filming set and even stayed in position, when they were enlighted from different positions with very bright light beams. Please note the the female, which I observed regularly actively searching for a position underneath the male (behavior not clearly visible in my footage). But it also conspicuously never stopped feeding (on an apple) during the copulatory process (very well visible in my footage), obviously to obtain enough nutrients for the production of eggs. A copulation in my couple is not a unique event, but is repeated regularly and can take hours.

 

Phoretic mites

 

Both genders carried bigger numbers of mites. These were phoretic deutonymphs of the taxon Astigmata (Acariformes, Acaridae). As never determined the mite species, as it was not clear, whether it represented a natural associate of these tropical beetles, or whether it was a species native to Germany, which for example was carried into the terrarium via Drosophila flies.

Copyrights Stefan F. Wirth, Berlin March 2017/ February 2019