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

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

Male and female of Histiostoma sachsi and unsuccessful mating with a „stranger“

Mites of the Acariformes vary in very different forms and life-strategies. One taxon of very tiny and soft-skinned mites is named Astigmata. Within them the familiy Histiostomatidae is especially rich of species, most of them surely not yet described or discovered.

 

Modyfied mouthparts and a specific mode of dispersal

 

These mites feed on microorganisms using a complex mouthpart-apparatus with multifunctional abilities. They can be found in habitats, which dry out quickly. When it’s getting too dry, a specific instar of the mites takes a ride on insects or other bigger arthropods for dispersal to a new and fresh habitat ( strategy called Phoresy).

Histiostoma sachsi is one of numerous (often closely related) long haired (in females) species. It was originally in 1957 described from cattle-dung. I found it in compost.

 

Long upper-setation in females and tactile camouflage (mimesis)

 

Adult females are characterized by a long setation on their uppersides. They use them to hold parts of the old nymphal cuticle and soil particles on their backs. This seems to be due to a strategy named mimesis or camouflage. It’s a tactile camouflage as an optical sense in this kind of microhabitats plays almost no role.

 

Normal and unusual copulation position, trial of an interspecific copulation

 

Males mate their females via a dorsal copulation opening and thus need to ride on them. In H. sachsi, that copulation opening is located very close to the hind-edge of the body. That way it is even despite of the camouflage cover accessible. It seems even slightly being elevated out of the body surface in order to surmount adjacent soil particles. This is an adaptation of this particular species. It might share such morphological characters only with very closely related (not yet described) species In other members of genus Histiostoma, the copulation opening is usually more centered related to the hind body.

The copulation position requires that males insert their aedeagus („penis“) into the copulation opening. They additionally use their legs to grasp into the females body. That kind of leg arrangement and thus the whole copulation position can differ from species to species.

This is why copulations between members of different species already fail, because the right copulation setting does not fit, nor does the shape of the aedeagous. Nevertheless the phenomenon of unsuccessful trials for interspecific copulations can sometimes be observed in laboratory cultures. Such a trial is also visible in this video, where a male of Histiostoma feroniarum (also appears in my compost samples regularly) tries to mate a female of H. sachsi. It cannot even almost get in a proper copulation position and seems to hold on to the dorsal camouflage cover of the female. it could only remain in a transverse position related to the female body and thus not get access to the copulation opening, normal would be a longitudinal position with the sameame orientation of female and male.

Adult mites of the family Histiostomatidae (Astigmata) and a „false“ copulation. Copyrights Stefan F. Wirth, Berlin December 2018. Please like my video also at Youtube, in case you like it.

 

Chemical communication and chemo-sensitive leg setation

 

Mites of the Astigmata communicate and find their general orientation due to chemo-sensitive setae, mostly on legs I and II, which are named solenidia. They are even on the magnification level of my footage well visible on the male’s legs. Although a direct body contact is not necessary for a innerspecific communication by chemically interpreting scents produced from mite glands, the observed male in my video repeatedly was seeking for intense body-contacts and obviously „observed“ his conspecific while doing so with its first two legs. This might have intensified the perception of pheromones.

It showed this behavior also, when passing by the „false copulation-pair“ described above. It additionally seemed to invest power in its leg movements as if it would try to remove the „competitor“ on the female, in this case even belonging to another species.

 

Competitive fights between males

 

That mites of the Histiostomatidae can use their strongly sclerotized first legs to fight under each other for an access to a female is known to me from my older observations about the species Histiostoma palustre and Histiostoma feroniarum.

 

Origin of the compost samples

 

The compost samples were collected in SW-Germany (Saarland in October 2018). The footage was recorded in December 2018 in Berlin.

 

Berlin December 2018, copyrights Stefan F. Wirth