The size, symmetry, and color saturation of a male guppy’s ornaments forecast his resistance to parasites

Sexually selected ornaments range from highly dynamic traits to those that are fixed during development and relatively static throughout sexual maturity. Ornaments along this continuum differ in the information they provide about the qualities of potential mates, such as their parasite resistance. Dynamic ornaments enable real-time assessment of the bearer’s condition: they can reflect an individual’s current infection status, or resistance to recent infections. Static ornaments, however, are not affected by recent infection but may instead indicate an individual’s genetically-determined resistance, even in the absence of infection. Given the typically aggregated distribution of parasites among hosts, infection is unlikely to affect the ornaments of the vast majority of individuals in a population: static ornaments may therefore be the more reliable indicators of parasite resistance. To test this hypothesis, we quantified the ornaments of male guppies, Poecilia reticulata,
before experimentally infecting them with Gyrodactylus turnbulli. Males with more left-right symmetrical black coloration and those with larger areas of orange coloration, both static ornaments, were more resistant. However, males with more saturated orange coloration, a dynamic ornament, were less resistant. Female guppies often prefer symmetrical males with larger orange ornaments, suggesting parasite-mediated natural and sexual selection act in concert on these traits.
Methods
Details on data collection and processing are given in the manuscript and supplement, including R script used.