A multi-trait analysis of the relationship between parasitism and female preference for orange ornaments in Trinidadian guppies ( Poecilia reticulata )

Several studies suggest that parasite-imposed selection favours elaborate sexual ornaments, as posited by the Hamilton–Zuk hypothesis. However, few have examined the prediction that selection by parasites also promotes heightened female preferences. We explored this prediction by asking whether the strength of female mate preference for the area of male orange coloration in wild Trinidadian guppy populations was associated with Gyrodactylus parasite infection metrics. We further examined how environmental factors might affect sexual selection, parasitism and their relationship in wild guppies. Our study, based on analyses of between 9 and 17 populations, offers preliminary evidence supporting the Hamilton–Zuk hypothesis and indicates interesting avenues for further research. We found that female preferences were stronger in populations exposed to higher Gyrodactylus intensities, but only if females preferred males with more orange coloration. The orange area was not associated with any parasite metric. This ornament varied with fish community composition, but the strength of female preference did not. Finally, Gyrodactylus prevalence increased with human disturbance, and intensity decreased in populations exposed to higher predation intensities and fish species richness. Our results suggest that parasitism may be one of several factors influencing sexual selection in guppies.