Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Rebecca J. Safran

Second Advisor

Robert P. Guralnick

Third Advisor

Andrew Martin

Fourth Advisor

David Stock

Fifth Advisor

Kim Hoke

Abstract

Colorful traits in animals often function to attract or compete for mates. However, the information gained by receivers (potential mates and competitors) is often unknown. Mechanisms of sexual selection (mate choice via indirect vs. direct benefits) make different predictions about the type information provided by these traits and therefore whether trait expression is primarily influenced by genetic (indirect benefits) or environmental variation (direct benefits). The goal of my dissertation research was to assess the role of genetic and environmental variation on melanin-based coloration and how these influences vary in response to different selective pressures. I conducted several field studies using two phenotypically divergent populations of barn swallows, Hirundo rustica. First, in the North American barn swallow (H.r. erythrogaster) in which ventral coloration is known to influence reproductive success, I used longitudinal data to demonstrate that ventral plumage coloration within an individual was consistent across developmental stages. Next, I conducted a cross-fostering experiment to tease apart the genetic and environmental influences on plumage color development in this subspecies. I found that coloration is quite sensitive to environmental variation, with low heritability suggesting females use this trait in mate choice to assess direct benefits provided by a mate. Finally, I replicated this cross-fostering experiment in the Czech Republic with a different subspecies of barn swallows (H.r. rustica) where the role of coloration in mate choice is unknown. I found that the relative genetic and environmental influences on color were similar in this divergent population; however, the genetic covariance structure of color traits differed. Together, these results demonstrate that coloration is influenced by developmental environment more than genetic environment. Thus, in North America, where females prefer males with dark plumage, coloration serves as a better signal of developmental conditions than genetic quality. Moreover, divergent selection on plumage coloration may explain the phenotypic differences among these populations, suggesting a role of sexual selection in the diversification of the barn swallow species complex.

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