One of the things Charles Darwin struggled with most in his Origin of Species was the apparent paradox of conspicuous ornaments in male animals. How could such extravagant structures be favored by natural selection when they are both costly to produce and dangerous to exhibit? Darwin suggested that males evolve conspicuous traits to satisfy females' "taste for the beautiful", giving ornamented males a mating advantage. Since Darwin's time, though, we have developed a sophisticated understanding of how such sexual selection operates in the unlikely case of males with a single attractive ornament (like a long tail) and females with a single mating preference (for long tails). Yet if males are sexually dimorphic - externally different from females - they are almost always flamboyant, with an array of conspicuous traits targeting different senses. How does a female integrate information about such an array into a decision about whom to mate with; and how do such decisions affect the evolution of conspicuous arrays?
This question is fundamental to understanding sexual selection, as well as how new species are formed and maintained. This project will address this question by taking advantage of a remarkable phenomenon in nature: streams in highland Mexico where two species of swordtail fish (family Poeciliidae: Xiphophorus birchmanni and X. malinche) interbreed, forming a hybrid zone. Why do females mate with the "wrong" species - does their taste for the beautiful cause them to make mistakes? Are females of one species more likely than the other to make such mistakes? To address these questions, data on the distribution of DNA markers in the wild will be combined with a variety of techniques for measuring female mating preferences. Computer-animated movies of males performing courtship behavior can be created to display any set of visual characteristics; female preferences can thus be measured for any combination of traits of either. These will reveal the extent to which preferences select for particular kinds of males in the wild, as well as how interactions among genes can counteract the effects of female mate choice on the evolution of male sexual traits.
This project provides unique opportunities for outreach in three main areas. (1) Collaboration with Mexican scientists through joint training of students and through continued work with an established lab in Mexico, (2) Training of minority undergraduates via a summer research program targeted at bilingual, Latino students, and (3) Local community outreach, through working with a local grassroots organization to promote sustainable use of freshwater resources.
