A new asymmetrical feather mite of the genus Michaelia trouessart, 1884 (Astigmata: Freyanidae) from the Neotropical Cormorant, Phalacrocorax brasilianus (Pelecaniformes)

Species of the feather mite genus Michaelia Trouessart, 1884 are notable for striking bilateral asymmetry in males, displayed in the structure of the anterior legs (both hetero- and homeomorphs) and the opisthosomal lobes (heteromorphs). A new species of this genus, Michaelia neotropica Hernandes and Mironov n. sp., is described from the Neotropical Cormorant Phalacrocorax brasilianus (Pelecaniformes: Phalacrocoracidae) from Brazil. It differs from M. urile (Dubinin, 1953) by having a narrower incision on the inner margins of the opisthosomal lobes anterior to setae h1, and relatively longer legs I with the ambulacrum reaching the midlevel of elongated tarsus II. A key to heteromorphic males of the genus Michaelia is provided.

Reasons for the development of bilateral asymmetry in several different lineages of feather mites are still enigmatic. A common aspect of these three unrelated groups of genera is that hosts of all of them are either aquatic birds or at least birds living in aquatic habitats. Thus, cormorants (Pelecaniformes: Phalacrocoracidae) are hosts of Dinalloptes and Michaelia; ibises and spoonbills (Pelecaniformes: Threskiornithidae) host Anisanchus, Hyperpedalloptes, and Freyanella; boobies (Pelecaniformes: Sulidae) host Sulanyssus; screamers (Anseriformes: Anhimidae) host Pavlovskiana; and one species of duck (Anseriformes: Anatidae: Nomonyx dominicus (Linnaeus, 1766)) is a host of the sole species of the genus Parafreyana. It is necessary to note that males of other feather mite species living on those same hosts are symmetrical. Thus, ibises host a number of completely symmetrical mites of the genera Ibidocolus Mironov, 1998, Ptyctalloptes Mironov, 2002, Spinicnemis Mironov, 2002, and Tauralloptes Mironov, 2002; cormorants host mites of the genera Plicatalloptes Dubinin, 1955 (Alloptidae), Scutomegninia Dubinin, 1951 (Avenzoariidae); and Nomonyx dominica also host Rectijanua oxyurae Gaud, 1961 (Rectijanuidae).
Since the asymmetry is expressed only in males, Dubinin (1951) suggested that it may enable them to maintain a more secure hold in the slanted corridors of the feather vanes during copulation with adult females or precopulatory guarding of female nymphs. Although plausible, this hypothesis still needs to be tested. The asymmetry of feather mites is displayed to a different extent and is the expression of male polymorphism; some male individuals (referred as heteromorphs) are strongly asymmetrical, while others (referred as homeomorphs) are almost or completely symmetrical. This can be a counterargument to the hypothesis of Dubinin.
In the present paper, we describe a new Michaelia species with strongly pronounced asymmetry in males from the Neotropical cormorant Phalacrocorax brasilianus (Gmelin, 1789).

MATERIALS AND METHODS
The material was retrieved from specimens of Phalacrocorax brasilianus found dead trapped on fishing nets in artificial lakes. The dead specimens were kept in a freezer and sent to the laboratory of Acari of São Paulo State University (UNESP), campus of Rio Claro. Bird specimens were washed and the liquid was filtered in paper filters; the mites were collected from the filters using a dissecting microscope, cleared in 30 % lactic acid for 24 h at 50°C , and mounted in Hoyer's medium according to the standard technique for small mites (Krantz and Walter 2009). After five days at 50°C, the slides were sealed with varnish. Drawings and measuring of mites were made with a Leica DM3000 microscope equipped with differential interference contrast (DIC) optics and a camera lucida.
General morphological terms and leg chaetotaxy follow Gaud and Atyeo (1996); idiosomal chaetotaxy also follows these authors with corrections to coxal setae proposed by Norton (1998). Measuring techniques for particular structures are indicated for each sex/morph. Depositories of type material: DZUNESP-RC -Departamento de Zoologia, Universidade Estadual Paulista, Rio Claro, SP, Brazil; ZISP -Zoological Institute, Russian Academy of Sciences, Saint Petersburg, Russia; USNM -National Insect and Mite Collection, National Museum of Natural History, Smithsonian Institution, located at the SEL-USDA, Beltsville, Maryland, USA.
Low Temperature Scanning Electron Microscopy (LT-SEM) -Specimens were observed in the LT-SEM as described in Dowling et al. (2010) and Bolton et al. (2014). Specimens preserved in 70 % ethanol were secured to 15 cm × 30 cm copper plates using ultra smooth, round (12 mm diameter), carbon adhesive tabs (Electron Microscopy Sciences, Inc., Hatfield, PA, USA). The specimens were frozen conductively, in a Styrofoam box, by placing the plates on the surface of a pre-cooled (-196°C) brass bar whose lower half was submerged in liquid nitrogen (LN 2 ). After 20-30 s, the holders containing the frozen samples were transferred to a Quorum PP2000 cryo-prep chamber (Quorum Technologies, East Sussex, UK) attached to an S-4700 field emission scanning electron microscope (Hitachi High Technologies Amer-ica, Inc., Dallas, TX, USA). The specimens were etched inside the cryotransfer system to remove any surface contamination (condensed water vapour) by raising the temperature of the stage to -90°C for 10-15 min. Following etching, the temperature inside the chamber was lowered below -130°C, and the specimens were coated with a 10 nm layer of platinum using a magnetron sputter head equipped with a platinum target. The specimens were transferred to a pre-cooled (-130°C) cryostage in the SEM for observation. An accelerating voltage of 5kV was used to view the specimens. Images were captured using a 4pi Analysis System (Durham, NC). Individual images were re-sized and placed together to produce a single figure using Adobe ® Photoshop CS 5.0. Males of the feather mite genus Michaelia are so bizarrely distorted that, when the first species "Dermaleichus heteropus Michael, 1881" was discovered, the author was reluctant to describe it based on a single male found, fearing it might be an abnormally distorted specimen (Michael 1881). He was only encouraged to describe the odd mite after he collected more specimens in the next year, and realized that all were identically asymmetrical. Michaelia species are large sized freyanids (females 600 -750 µm, males 800 -1090 µm in length). There are two male morphs in these mites, homeomorphs and heteromorphs; both morphs have asymmetrical anterior legs, but the opisthosomal lobes are asymmetrical only in heteromorphs. Females and immatures are absolutely symmetrical and are relatively wider and shorter than both male morphs.
Differential diagnosis -The new species, Michaelia neotropica Hernandes and Mironov n. sp., is close to M. urile (Dubinin, 1953) by the absence of a retrograde spur on both tarsi I and a ventral spine on the femur of the smaller leg I in heteromorphic males. A spur on tarsus I is present in heteromorphic males of M. amplosinus (Gaud, 1970) and M. heteropus, and a ventral spine on femur I is present in M. heteropus and M. microcarbonis (Dubinin, 1953). Heteromorphic males of Michaelia neotropica differ from those of M. urile by having a narrower incision on opisthosomal lobes anterior to setae h1 with its margins almost touching each other, and by the relatively longer legs I with their ambulacrum reaching the midlevel of tarsus of the elongated leg II. In heteromorphic males of M. urile, the lobar incisions anterior to setae h1 are wide, rounded, about half as wide as long, and the ambulacra of tarsi I reach only the level of solenidion ϕ on tibia of enlarged leg II. Considering the closest species in relation to the new one being described (Michaelia urile vs M. neotropica n. sp.), differences between homeomorphic males are minimal, as far as it is detectable from the original descriptions. As far as we know, females are very hardly distinguishable between all species, and we prefer to avoid mentioning preliminary differences at this point.
Etymology -The specific epithet refers to the common name of the host, the Neotropical Cormorant.