Parasites generally have a negative influence on the color expression of their hosts. Sexual selection theory predicts resistant high-quality individuals should show intense coloration, whereas susceptible low-quality individuals would show poor coloration. However, intensely colored males of different species of Old and New World lizards were more often infected by hemoparasites. These results suggest that high-quality males, with intense coloration, would suffer higher susceptibility to hemoparasites. This hypothesis remains poorly understood and contradicts general theories on sexual selection. We surveyed a population of Sceloporus occidentalis for parasites and found infections by the parasite genera Lankesterella and Acroeimeria. In this population, both males and females express ventral blue and yellow color patches. Lankesterella was almost exclusively infecting males. The body size of the males significantly predicted the coloration of both blue and yellow patches. Larger males showed darker (lower lightness) blue ventral patches and more saturated yellow patches that were also orange-skewed. Moreover, these males were more often infected by Lankesterella than smaller males. The intestinal parasite Acroeimeria infected both males and females. The infection by intestinal parasites of the genus Acroeimeria was the best predictor for the chroma in the blue patch of the males and for hue in the yellow patch of the females. Those males infected by Acroeimeria expressed blue patches with significantly lower chroma than the uninfected males. However, the hue of the yellow patch was not significantly different between infected and uninfected females. These results suggest a different effect of Lankesterella and Acroeimeria on the lizards. On the one hand, the intense coloration of male lizards infected by Lankesterella suggested high-quality male lizards may tolerate it. On the other hand, the low chroma of the blue coloration of the infected males suggested that this coloration could honestly express the infection by Acroeimeria.
Keywords: : animal communication; Hamilton and Zuk; coloration; parasites; sexual selection.