Belongs within: Psoroptidia.
The Pterolichidae are a group of astigmatine mites found living in the feather vanes of a range of bird orders. Females either have the legs inserted laterally or have anterior tarsi less than twice the length of the tibiae, and lack ad setae.
A little piece of feathery paradise
Published 13 June 2023
I don’t think I would surprise anyone by saying that the evolution of feathers was a revolutionary factor in the evolution of birds. But what may be less appreciated is that it was also a revolutionary factor in the evolution of mites. The complex topographies of feathers on birds provided a wealth of new micro-habitats, ones that mites were all too ready to expand into and exploit. Some remained attached to the cozy, sheltered warmth of the bird’s skin. Others explored the tangled thickets of down feathers, swinging from plume to plume like microscopic gibbons. Still others entered the hollows at the centre of quills. And then there were those that occupied the most challenging micro-environment of all, the exposed vanes of the wings. Among the most diverse families of vane-living mites are the Pterolichidae.
For the ancestors of pterolichids, occupying the wings demanded a host of adaptations to cling in place. A flattened body and reduced setae on the dorsal surface reduced air resistance. Hardened dorsal surfaces resisted damage from preening and/or the feathers moving against one another as the wings opened and closed. Laterally directed legs and powerful leg muscles (associated with enlargement of the epimeres, internal cuticular ridges that anchor the muscles) assisted in gripping the flat surface of the vanes, as did sucker-like ambulacral discs at the ends of the legs. Enlarged setae at the end and often sides of the body helped anchor the mite in place. Males have a pair of sucker-like structures towards the end of the venter that are used to grip the female when mating.
Though pterolichids are currently recognized as the most diverse family of feather-vane mites, this picture may be a little misleading. The Pterolichidae are primarily defined by the absence of derived features beyond those common to all feather-vane mites, so are likely to be paraphyletic to related ‘families’. Nevertheless, species assigned to the pterolichids have been described from most orders of birds, with a particularly high diversity on Galliformes (OConnor 2009). Mite species are closely associated with their particularly host species with little evidence for transmission across lineages. An extreme example of this is brood-parasitic cuckoos which have their own mite species, transmitted from one individual to another during copulation, and rarely carry mites from their host parents (Dabert & Mironov 1999). Many bird species may carry more than one mite species, specialised for distinct micro-habitats. For instance, the hoatzin is host to two species, Opisthocomacarus umbellifer and Stakyonemus hystrix (Atyeo & Gaud 1971). Stakyonemus has long, barbed lateral setae whereas in Opisthocomacarus these setae are leaf-like with finely serrate edges. Stakyonemus lives closer to the midline of the feather vane, where its large setae wedge between the thicker bases of the feather ridges, whereas Opisthocomacarus’ leaf-like setae are better suited for gripping the finer parts of the ridges towards the feather’s outer margin*.
*Offhand, Atyeo & Gauld (1971) believed that the hoatzin feather mites seemed over-adapted for clinging to such a weak flier, and suggested that the morphology of its mites might argue for a descent of hoatzins from more strongly flying ancestors. Personally, I always feel a bit skeptical about such arguments based on retention of ‘obsolete’ characters, and feel more skeptical the longer the supposed retention.
The diet of pterolichids consists of glandular secretions coating the feathers, together with debris such as pollen and fungal spores caught in the barbs. They may also eat broken fragments of feather. The impact of pterolichids on their host is usually minimal (one species, Struthiopterolichus bicaudatus, may be considered a pest on ostrich farms due to their effect on plume quality). Indeed, in some cases there may even be a positive correlation between mite numbers and host condition (Krantz 2009). This may indicate that the birds benefit from the mites cleaning their vanes… or it may just be that healthier hosts can better handle the load.
Systematics of Pterolichidae
<==Pterolichidae |--Opisthocomacarus umbelliferWP99 |--GoniodurusWP99 |--FalcolichusWP99 |--Grallobia fulicaeDW10 |--Xoloptes blaszakiDW10 |--Ctenodiscopus laurentiiNK94 |--Ascetolichus Pérez & Atyeo 1990H98 | `--A. ruidus Pérez & Atyeo 1990H98 |--Leipobius Atyeo 1992H98 | `--L. ocellatus Atyeo 1992H98 |--Aegothelichus Atyeo 1979H98 | `--A. deficiens Atyeo 1979H98 |--Lorilichus Atyeo & Gaud 1991H98 | `--L. cultriventris (Trouessart 1884) (see below for synonymy)H98 |--Montchadskiana Dubinin 1951H98 | `--M. pluvialisi Dubinin 1951H98 |--Pseudalloptinus Dubinin 1956H98 | `--P. milvulinus (Trouessart 1884) [=Pterolichus aquilinus var. milvulinus, Cynthiura milvulina]H98 |--Sideroferus Gaud & Atyeo 1996H98 | `--S. lunula (Robin in Robin & Mégnin 1977) [=Pterolichus lunula, Protolichus lunula]H98 |--Echinozonus Atyeo & Pérez 1991H98 | |--E. leurophyllus Atyeo & Pérez 1991H98 | `--E. longisetosus Atyeo & Pérez 1991H98 |--Protolichus Mégnin & Trouessart 1884H98 | |--P. crassior (Trouessart 1884) [=Pterolichus crassior]H98 | `--P. distensus Favette & Trouessart 1904H98 |--Apexolichus Gaud & Atyeo 1996H98 | |--A. affinis (Mégnin & Trouessart 1884) [=Pterolichus affinis]H98 | |--A. falculiger (Trouessart 1884) [=Pterolichus falculiger, Protolichus falculiger]H98 | `--A. favettei (Trouessart 1899) [=Pterolichus favettei, Protolichus favettei]H98 |--Pterolichus Robin 1868H98 | |--P. (Pseudalloptes) bimucronatus Trouessart 1884T05 | |--P. chiragricus Mégnin & Trouessart 1884H98 | |--P. obtususDW10 | |--P. phylloproctus Mégnin & Trouessart 1884 (see below for synonymy)H98 | `--P. velifer Mégnin & Trouessart 1884 [=Protolichus velifer]H98 `--Rhytidelasma Gaud 1966H98 |--R. cornigeraWP99 |--R. dilatataNK94 |--R. mesomexicanaWP99 |--R. spathuligera (Trouessart 1884) [=Pterolichus spathuliger, Pseudalloptes spathuliger]H98 `--R. urophilaWP99
Lorilichus cultriventris (Trouessart 1884) [=Pterolichus cultriventris, Pseudalloptes cultriventris, Rhytidelasma cultriventris]H98
Pterolichus phylloproctus Mégnin & Trouessart 1884 [incl. Pt. phylloproctus var. minor Mégnin & Trouessart 1884, Protolichus minor]H98
*Type species of generic name indicated
Atyeo, W. T., & J. Gaud. 1971. Feather mites (Analgoidea: Pterolichidae) of the hoatzin (Aves: Galliformes). American Midland Naturalist 86 (1): 152–159.
Dabert, J., & S. V. Mironov. 1999. Origin and evolution of feather mites (Astigmata). Experimental and Applied Acarology 23: 437–454.
[DW10] Dabert, M., W. Witalinski, A. Kazmierski, Z. Olszanowski & J. Dabert. 2010. Molecular phylogeny of acariform mites (Acari, Arachnida): strong conflict between phylogenetic signal and long-branch attraction artifacts. Molecular Phylogenetics and Evolution 56 (1): 222–241.
[H98] Halliday, R. B. 1998. Mites of Australia: A checklist and bibliography. CSIRO Publishing: Collingwood.
Krantz, G. W. 2009. Habits and habitats. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 64–82. Texas Tech University Press.
[NK94] Norton, R. A., & J. B. Kethley. 1994. Ecdysial cleavage lines of acariform mites (Arachnida, Acari). Zoologica Scripta 23 (3): 175–191.
OConnor, B. M. 2009. Cohort Astigmatina. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 565–657. Texas Tech University Press.
[T05] Trägårdh, I. 1905. Monographie der arktischen Acariden. In: Römer, F., & F. Schaudinn (eds) Fauna Arctica. Eine Zusammenstellun der arktischen Tierformen, mit besonder Berücksichtigung des Spitzbergen-Gebietes auf Grund der Ergebnisse der Deutschen Expedition in das Nördliche Eismeer im Jahre 1898 vol. 4 pp. 1–78. Gustav Fischer: Jena.
[WP99] Walter, D. E., & H. C. Proctor. 1999. Mites: Ecology, Evolution and Behaviour. CABI Publishing: Wallingford (UK).