Cloacal microparasites and sexual selection in three Australian passerine species

Cloacal microparasites such as viruses, bacteria and fungi are expected to condition choice of sexual partner, as they can not only affect the expression of secondary sexual traits used in courtship, but they could be also directly transmitted to partners through copulation. We investigated the distribution of three cloacal microparasites (the bacterium Chlamydia psittaci and the yeasts Candida albicans and Kloeckeria sp.) among males and females of the sexually plumage dichromatic Malurus cyaneus and Sericornis frontalis, and the plumage monochromatic Manorina melanophrys. Males tended to be more parasitized than females within species, but the effect was stronger for the sexually dichromatic S. frontalis than for the sexually monochromatic M. melanophrys. In addition, parasitized males of the sexually dichromatic M. cyaneus had more conspicuous ear tufts (a secondary sexual trait used in courtship) than unparasitized males. The above evidence suggest that mate choice may involve a cost in terms of transmission of cloacal microparasites.