Behavioral Dysfunction and the Evolution of Reproductive Isolation between Species

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

The breeding of different species, called hybridization, is a common phenomenon that raises a fundamental problem: if species can interbreed, what maintains their distinct characteristics and keeps species separated? Answers to this question have usually focused on hybrid offspring: if hybrids cannot survive or reproduce, then gene exchange between species will be restricted and species are kept separate and distinct. To date, most work exploring the possibility that hybrids perform poorly focuses on hybrid physiology and morphology. Few studies have investigated whether hybrids show altered behaviors that prevent them from reproducing and thereby limiting further gene exchange. The proposed work evaluates the impact of behavior on hybridization in spadefoot toad species. By doing so, the research will provide important insights into how behavior acts to help maintain species boundaries. The research has critical implications for understanding biodiversity and conservation of endangered species that could hybridize with others. In carrying out this work, the PI will train undergraduates and graduate students in both research techniques and public outreach. Indeed, the PI and her lab members will engage in public outreach in North Carolina and beyond through work at the North Carolina Museum of Natural Sciences. Specifically, they will give talks in the museum's Daily Planet Theater, which provides live programming to museum visitors and live streaming of presentations to K-12 schools, senior centers, and libraries throughout North Carolina. Videos of these presentations are uploaded as podcasts onto iTunes University, on which the museum receives 20,000 downloads a month, and to the museum's website, which receives approximately one million hits per year; programs distributed via the museums website are available to users anywhere. Under the widely used biological species concept, species are defined as groups of organisms that do not exchange genes; they possess evolved features that prevent gene flow between them. A major class of such 'isolating mechanisms' includes traits that engender low fitness in hybrid offspring, thereby preventing them from backcrossing to the parent populations. Because hybrid maladaptation is crucial to the speciation process, clarifying the causes of hybrid maladaptation is central to understanding speciation. Most speciation research has focused on three causes of hybrid maladaptation: decreased survival, reduced fertility, and decreased likelihood of succeeding in either parental niche. In contrast, the role of behavior in hybrid maladaptation, specifically that hybrids might exhibit dysfunctional reproductive behavior, has been relatively understudied. Yet, viable, fertile hybrids might fail to respond appropriately to courtship signals, or, alternatively, they might express mate preferences that reduce their likelihood of mating with fitness-enhancing mates. Such dysfunctional reproductive behavior could render viable, fertile hybrids 'behaviorally sterile', thereby acting as a potentially key isolating mechanism between species. The proposed work will ascertain if hybrid spadefoot toads display dysfunctional reproductive behaviors, and whether such behavior explains patterns of gene exchange in natural populations. Using two species of naturally hybridizing toads, the research will: 1) evaluate hybrid responses to breeding opportunities; 2) establish hybrid mate preferences; 3) measure the fitness consequences of mate preferences; 4) ascertain whether hybrids invest less in reproduction; and 5) determine patterns of hybrid mating in the field. Together, the projects will identify behavior's role in the origins and maintenance of species boundaries.