Choosing a mate is one of the most far-reaching decisions an animal can make. A female's mate choice can influence not only which male traits get passed on to the next generation, but also the formation of new species or the fusion of two species through hybridization. Mating preferences are complex, with females paying attention to numerous different male characteristics, and females often prefer male trait combinations never found in nature. How do complicated female mating preferences drive male trait evolution? This project takes advantage of remarkable natural hybrid zones between two species of swordtail fish in the Sierra Madre Oriental of central Mexico. Males of the two species are strikingly different in physical appearance, and females of the two species show strong differences in their preferences for male characters. Mating preferences for multiple male traits will be evaluated by presenting females with computer-animated clips of males. Genetic mapping will be used to identify which sets of genes are associated with male traits and female preferences. This genetic information will then be used to test how traits and preferences are associated in the wild. This project will directly connect the psychology of mate-choice decisions with the evolutionary consequences of these decisions. The project will sustain collaboration with Mexican researchers, mentoring of minority undergraduates, and conservation, sustainable development, and outreach efforts in rural Mexico.
New advances in biological research have changed the way scientists think about evolution. Rather than species simply branching off from each other and forming different lineages, we now realize that hybridization - exchanging genes among lineages - plays a major role in how species diversify and how they adapt to novel environments. Hybridization ultimately depends on individual choices. Our research focuses on why individuals sometimes choose to mate wtih a partner of a different species, and how these individual decisions can have long-term evolutionary consequences. We focus on two species of livebearing freshwater fish, the highland swordtail and the sheepshead swordtail, distributed along mountain streams in the Sierra Madre Oriental of central Mexico. Our research has shown that human impacts, notably pollution, increase the likelihood of hybridization between females of one species and males of the other species. Once hybridization occurs, it opens Pandora's box, since hybrid males are more attractive to females across the board. and since females learn their mating preferences depending on male appearance. We therefore see hybrids long after streams have been cleaned up, and in areas that were never impacted by human activities, because hybrids are mating back to the two parental species. Hybrids are therefore exchanging genes back and forth between these two species. Pollution isn't solely to blame for this; sequencing whole genomes reveals episodes of hybridization among swordtail species going back hundreds of thousands of years. Our research involves students, faculty, and community members from around the U.S. and the world, including aquarium hobbyists and undergraduate students. Our field work is based at the CICHAZ research station in a primarily indigenous area of central Mexico, and we have shared our research with local stakeholders and facilitated use of the station by other researchers studying local issues like municipal government and water management.
