Meeting Abstract
133.2 Monday, Jan. 7 Proximate and ultimate mechanisms for intraspecific variation in male body size and sexual size dimorphism in the brown anole (Anolis sagrei)) COX, R.M.*; DAUGHERTY, C.; PRICE, J.; MCGLOTHLIN, J.W.; CALSBEEK, R.; University of Virginia; University of Virginia; University of Virginia; Virginia Tech; Dartmouth College rmc3u@virginia.edu
Intraspecific variation can arise from genetic changes due to variation in selection and/or from phenotypic plasticity in response to local environmental conditions. These processes can differentially impact males and females, leading to intraspecific variation in sexual dimorphism. We combined studies of natural selection in the wild with common-garden studies in captivity to investigate the proximate and ultimate basis of intraspecific variation in male-biased sexual size dimorphism (SSD) in two island populations of the brown anole, Anolis sagrei. In the wild, SSD was significantly greater on Exuma than on Eleuthera. This difference arose primarily from intraspecific variation in the growth and body size of adult males, rather than females. However, patterns of viability selection on body size were highly congruent on both islands: females experienced stabilizing selection favoring intermediate size, whereas males experienced directional selection favoring larger size. Thus, sex-specific selection matched the overall pattern of male-biased SSD, but population differences in the magnitude of SSD were not associated with local differences in selection. Body condition was significantly lower on Eleuthera than on Exuma, suggesting that intraspecific variation in SSD reflects local variation in energy availability that disproportionately impact males on account of their greater absolute energy requirements. Nonetheless, our common-garden experiment indicated a strong genetic component to island differences in the growth and body size of adult males. We discuss these results in light of current research targeting the quantitative genetics of growth and sexual dimorphism.
