Asymmetry and polymorphism in males of the feather mite Michaelia neotropica Hernandes and Mironov (Acariformes: Astigmata: Freyanidae)

Polymorphism is common among male astigmatan feather mites (Acariformes: Astigmata: Analgoidea, Pterolichoidea). The more highly modified morph (the 'heteromorphic' male) typically shows symmetrical hypertrophy of one or two pairs of legs. However, males of several genera of feather mites show an additional type of polymorphism in which some males have elaborate modifications only on the right side of the body, and others on the left. We examined male polymorphism in Michaelia neotropica Hernandes and Mironov, a symbiont of New World cormorants (Aves: Phalacrocoracidae), to determine the frequency of all morph types, whether some morph types more frequently co-occurred than others, and whether left- or right-handedness was associated with the particular location of the male on the host's wing. We also tested whether certain male morphs were more likely to be found with females. Of 110 male M. neotropica from nine culled cormorants from Alberta, Canada, 87 were homeomorphic and 23 were heteromorphic. The ratio of left- to right-handedness was exactly 50:50. There were no significant associations between homeo- and heteromorphy and left- or right-handedness. Left-handed males were most commonly found on the host's right wing, and right-handed males on the left wing. We discuss the possible function of asymmetry in these mites and suggest that left- and right-handedness is not genetically defined but rather is a product of differential stresses on muscles during a male's nymphal stages.