Parasitized female guppies do not prefer showy males.

In many species male sexual characteristics are known to be affected negatively by parasites, which render their hosts unattractive to females, but how parasites affect the mating decisions of their female hosts has received little attention. The monogenean parasite Gyrodactylus turnbulli reduces the sexual display and colour intensity of male guppies, Poecilia reticulata, which makes them less attractive to females. Here, I examine how these parasites affect the mate choice behaviour of their female hosts. Virgin females were experimentally exposed to G. turnbulli and allowed to choose between an attractive and an unattractive male in a simultaneous choice test. Infected females were significantly less discriminatory than healthy ones and their level of activity during choice trials was reduced with increasing parasite load, suggesting an energetic constraint imposed by the parasites. This result implies that sexual selection pressure for male showiness is diminished, which is consistent with recent theoretical models. Copyright 1999 The Association for the Study of Animal Behaviour.