[Morphological adaptations of acariform mites (Acari: Acariformes) to permanent parasitism on mammals]

The external morphological adaptations to parasitism in acariform mites (Acari: Acariformes), permanently parasiting mammals, are briefly summated and analyzed. According to several external morphological criteria (structures of gnathosoma, idiosoma, setation, legs and life cycle), the following six morphoecotypes were established: skin mites (i)-- Cheyletidae, Chirorhynchobiidae, Lobalgidae, Myobiidae, Myocoptidae (the most part), Rhyncoptidae, Psoroptidae; fur mites (ii)--Atopomelidae, Clirodiscidae, Listrophoridae, Myocoptidae (Trichoecius only); skin burrowing mites (iii)--Sarcoptidae; intradermal mites (iv) - sorergatidae and Demodicidae; interstitial mites (v) - pimyodicidae; respiratory mites (vi) - reynetidae, Gastronyssidae, Lemurnyssidae, Pneumocoptidae. In the case of prostigmatic mites, the detailed reconstruction of the origin and evolution of "parasitic" morphoecotypes is possible due to the tentative phylogenetic hypotheses, which were proposed for the infraorder Eleutherengon, a, including the most part of the permanent mammalian parasites among prostigmatic mites (Kethley in Norton, 1993; Bochkov, 2002). The parasitism of Speleognathinae (Ereynetidae) in the mammalian respiratory tract arose independently of the other prostigmats. It is quite possible that these mites switched on mammals from birds, because they are more widely represented on these hosts than on mammals. The prostigmatic parasitism on mammalian skin seems to be originated independently in myobiids, in the five cheyletid tribes, Cheyletiellini, Niheliini, and Teinocheylini, Chelonotini, Cheyletini, and, probably, in a cheyletoid ansector of the sister families Psorergatidae-Demodicidae (Bochkov, Fain, 2001; Bochkov, 2002). Demodicids and psorergatids developed adaptations to parasitism in the skin gland ducts and directly in the epithelial level, respectively in the process of the subsequent specialization. Mites of the family Epimyodicidae belong to the phylogenetic line independent of other cheyletoids. These mites possess the separate chelicerae and, therefore, can not be included to the superfamily Cheyletoidea. It is not quite clear whether they were skin parasites initially or they directly switched to parasitism from the predation. The phylogeny of sarcoptoid mites (Psoroptidia: Sarcoptoidea) is not developed, however, some hypotheses about origin and the following evolution of their morphoecotypes can be proposed. We belive that astigmatic mites inhabiting the mammalian respiratory tract transferred to parasitism independently of other sarcoptoids. The idiosoma of these mites is not so much flattened dorso-ventrally and has proportions which are similar to hose of free-living astigmatids. Moreover, in the most archaic species, the legs are not shortened or thickened as in the most parasites. The disappearance of many morphological structures in these mites, probably, happened parallely with some other sarcoptoids due to their parasitic mode of life. The skin inhabiting sarcoptoids belong to the "basic" morphoecotype, and all other sarcoptoid morphoecotypes, excluding respiratory mites, are derived from it. Some mites of this morphoecotype live on the concave surfaces of the widened spine-like hairs of the rodents belonging to the family Echimyidae (mites of the subfamily Echimytricalginae), in the mammalian ears (some Psoroptidae) or partially sink into the hair follicles (Rhynocoptidae). Finally, mites of the family Chirorhynchobiidae live on the bat wing edges attaching to them by their "ixodid-like" gnathosoma. The fur-sarcoptoids, probably, originated from the skin mites. This morphoecotype is divided onto two subtypes: mites with the dorso-ventrally flattened idiosoma (subtype I) and mites with the teretial idiosoma (subtype II). Each "fur-mite" family includes mites of the both subtypes. All mites of the first subtype belong to the early derivative lineages in their families. Among listrophorids such early derivative lineage is represented by the subfamily Aplodontochirinae (Bochkov, OConnor, 2006), and among Chirodiscidae--by mites of the subfamilies Chirodiscinae, Schizocoptinae, and Lemuroeciinae. Among the "fur" astigmatid families, the family Atopomelidae. probably, is the most archaic, and the most part of atopomelids belongs to the first subtype. However there are several more specialized atopomelid genera belonging to the second subtype, Atopomelus, Dasyurochirus, Lemuroptes, Murichirus, Metachiroecius etc. We believe that mites of the first subtype are represented by the "intermediate" forms between skin mites and mites of the second subtype. Some skin sarcoptoids transferred from skin parasitism to burrowing of the host skin (Sarcoptidae). The established morphoecotypes are partially corresponding to some morphoecotypes established by Mironov (1987) for feather mites. Our morphoecotypes of skin and skin burrowing mites perfectly correspond to Mironov's epidermoptoid and knemidocoptoid morphoecotypes, respectively. The proctophylloid morphoecotype (mites living on the wing feathers), which is the most widely represented within feather mites, has an analogy among mammalian mites - the subfamily Echimytricalginae. The analgoid (mites living in the down feathers) and dermoglyphoid (mites living in the feather quills) morphoecotypes have no analogues among mammalian mites for the obvious reasons. It is interesting why some microhabitats on the host body are not still occupied by prostigmatic or astigmatic mites. We believe that the nutrition is the main limitative factor here. The parasitic prostigmates evolved from predators and, therefore, feed on content of the living cells. They need the direct contact with the live tissues of the host and they belong, therefore, to the morphoecotypes represented by the respiratory, skin, gland duct, intradermal, and interstitial mites. Whereas, the most part of the skin inhabiting astigmats feed on the dead epithelial scales. For this reason these mites, so easily colonized fur of their hosts and feed on the hair grease there. On the other hand, some sarcoptoids transferred to the true parasitism and feed on the cambial cells of the skin epithelium. More over we do not know exactly about nutrition of rhyncoptids yet.