Evolution of sexually selected traits and mating preferences

A decade ago the conventional wisdom regarding the effects of mate choice on the joint evolution of mating preferences and preferred traits suggested that sexual and natural selection will eventually reach evolutionary balance. Although this balance could be reached with different combinations of mate choice strength and elaboration of the preferred trait, the inevitability of balance per se seemed robust to the details of inheritance. My analyses of more realistic genetic models revealed that the development of a balance is in fact highly sensitive to even the weak evolutionary influences of Mendelian segregation and allelic dominance. These results along with subsequent analyses of other models caused a paradigm, once considered to be genetically insensitive, to be replaced by its opposite, namely, a strong dependence of evolutionary pattern on genetic detail.

My research has also considered the effect of social system on mate choice and sexual selection. For example, the structure of mating aggregations (usually of males) determines the extent to which a member of the choosing sex (typically female) can exercise mate choice. If aggregations contain few males and are relatively isolated, females would tend to survey fewer potential mates than they would if aggregations were closely spaced and attended by many males. My theoretical analyses, which appear to be robust to genetic details, predict that the effectiveness of sexual selection declines as mate choice becomes more limited. This suggests that sexually selected traits are more likely to evolve in species where females have unrestricted mate choice. Preliminary consideration of ornithological studies is consistent with this prediction. I have more recently been working with an undergraduate honors student, Scott Williamson, who has been analyzing a related mathematical model that describes the evolution of the mating aggregations themselves.

I have also investigated the role of age in sexual selection. While there are numerous examples of sexually selected traits whose expression depends on an individual's age or social status, genetically based theory of sexual selection has not yet considered the influence of demographic age- or stage-structure. I am working to fill this promising gap in collaboration with an avian systematist, Dr. Richard Prum. Our preliminary comparisons of my initial theoretical predictions concerning the causes of delayed maturation of full breeding plumage (viz., that high juvenile mortality leads to the evolution of delayed plumage maturation) with data from the embirizid family has encouraged us to expand the theoretical and empirical scope of this project.

Selected publications in this research area