The *evolution of multiple sexual signals in a passerine: Trait structure and selection in a dynamic world

The evolution of multiple sexual ornaments is perplexing because costs associated with trait production should favor single trait that best predicts male quality. Many hypotheses have been proposed to explain the ubiquity of such traits, but few have received empirical attention. I focus on the evolution of multiple sexual ornaments in Lark buntings, Calamospiza melanocorys , with particular attention to dynamic male-male competition and temporal variation in female preferences. In the first chapter I demonstrate that there is considerable variation in the seven traits I focused on and that these traits were mostly independent from one another with little evidence for trade-offs among traits. Individuals who returned across years show some trait consistency suggesting a genetic component of those traits. Change in these traits was linked to environmental factors that in some cases affects all returning birds. In chapter two I focused on male-male competition using both observational and experimental tests of dominance and found that multiple ornaments can be selected for as badges of status. I found that while wing patch size was a good badge of status at long ranges, body color and the proportion of black feathers were a better close range signals. The proportion of black feathers on the rump was only useful at close range and may allow individuals flexibility in status to fit appropriate social contexts. In chapter three I investigated temporal variation in female preferences. I found that traits associated with female choice of social mate varied from year to year. No two years were alike, some traits were preferred in some years but not others, and body color and wing patch size were preferred as larger values one year and smaller values another year. Change in traits associated with female choice was not due to influences of male competition, evolution of preferences, or female age but rather was the result of individual females changing their preferences from year to year. Shifts in female preferences were associated with the need for male care, although genetic evidence suggests females are making different choices for traits of actual sires.