Dissertation Research: The Evolutionary Genetics of Sexual Dimorphism

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

One of the great mysteries of the natural world concerns why males and females of the same species often differ in many morphological characters. Sexual size dimorphism (SSD), or the difference in mean body size between the sexes, is of particular interest since body size plays a central role in the fitness of an individual. With the advent of new statistical tools and conceptual advances, investigations into the evolution of SSD have moved from the traditional temporally static, single pressure, single sex perspective, to the more robust view of multiple selective forces interacting in both sexes across many generations. However, to fully interpret the evolutionary implications of these selective pressures, one must also know the underlying genetic architecture of male and female body size. This is true since genetic architecture may alter or constrain a dimorphic response to selection. Unfortunately, few studies have expanded their investigation of SSD beyond the scope of the selective pressures involved, creating a dearth of information regarding the evolutionary genetics of dimorphism. The objectives set forth in this proposal will investigate the underlying genetic structure of a sexually dimorphic trait that is known to be under selection from multiple sources. This study will employ an empirical quantitative genetic approach to generate for both sexes the variance covariance matrices (G-matrices) for body size and two other important correlated traits under selection. This will permit comparison between the sexes for differences in genetic architecture and tests for significant correlations between the sexes for homologous traits that may constrain dimorphic evolution. In addition, when G-matrices are coupled with selection gradients that describe the direction and intensity of selection, one can predict if genetic covariances will have a significant effect on trait evolution, if this effect constrains or reinforces trait evolution, and if dimorphism is still evolving. The results of this study will be of general interest as they will likely have bearing on gender-based differences for many other traits in many other systems.