2014 AOU talk

A central theme of evolutionary research is to understand the source and function of phenotypic variation. For most phenotypic traits, sources of variation can be partitioned into genetic or environmental variation. Identifying the proportion of variance due to these components allows for predictions regarding phenotypic responses to variable environments and selection to be made. Barn swallow subspecies have divergent phenotypes and it appears that the focal trait for female preferences has also diverged. We examined the sources of phenotypic variation of melanin-based ventral plumage in two populations of barn swallows: North America (Colorado) and Europe (Czech Republic). In North America, male coloration is the target of sexual selection with darker males achieving higher reproductive success. However, it is unclear what role coloration plays in mate choice decision for our study population in the Czech Republic. In both populations, we found that coloration is explained by both genetic and environmental variation. However, comparative analyses suggest that there is no divergence among these populations in the additive genetic covariance structure for color traits. These results provide insight into the possible mechanisms that lead to phenotypic divergence between these recently diverged subspecies.