Is Color Related to Parasite Load in a Sexually Dichromatic Neotropical Toad?

Abstract: Research on anuran parasites often focuses on the description and identification of parasites and demonstrating that parasitic infection can have deleterious effects on the health of amphibians. There is comparatively little research on how parasitism influences evolutionary dynamics such as sexual selection. Here, we explore anuran blood parasites with a focus on parasite-mediated sexual selection. The Hamilton–Zuk hypothesis posits that parasite–host coevolution drives sexual ornamentation of hosts, and that the degree of ornament expression honestly signals heritable parasite resistance. Although the Hamilton–Zuk hypothesis has received support in a number of animal taxa, it has received little attention in amphibians. Neotropical Yellow Toads (Incilius luetkenii) are sexually dichromatic toads with an unusual sexual ornament: males turn from cryptic brown to bright lemon yellow for a very short period during the brief breeding season. In this study, we identify blood parasites in male Neotropical Yellow Toads, and we investigate one component of the Hamilton–Zuk hypothesis by comparing skin color and body condition to blood parasite levels. We found four types of parasites. Apicomplexa and frog erythrocytic virus were the most common, infecting 73% and 46% of toads, respectively, whereas Nematoda and bacteria were found in 27% and 36% of toads, respectively. We found negative relationships between parasites and male color: males infected with fewer Apicomplexa and Nematoda had higher yellow saturation, and males with fewer Nematoda had longer-wavelength hue. In contrast, we found one positive relationship between parasites and male color: males infected with higher levels of frog erythrocytic virus had higher brightness. Our results suggest that parasites may influence sexual traits in this species, but that the relationship is complex. This research contributes to our understanding of amphibian host–parasite coevolution by demonstrating a relationship between parasites and host coloration.