Understanding the origins of the Earths tremendous biodiversity is a major goal of evolutionary biologists. Biodiversity has two major elements: the great number of species of organisms that exist, and the great variety of traits that have divergently evolved in different species to adapt them to their particular ecological challenges. In recent years, it has become appreciated that the same process that yields diversity in traits may also promote the formation of species-level diversity. That is, ecologically adaptive divergence is now believed to promote species formation (speciation). This project adopts novel approaches to evaluate how it is that the different ecological challenges experienced by various herbivorous leaf beetle populations (host forms) can cause those populations to interbreed and exchange genes at a reduced rate, thus setting them on the path to speciation. These host forms live their entire lives on one or another tree species. This project studies three host forms: those associated with specific species of maple, alder, and willow trees in nature. These host forms are known to prefer to use their native hosts (e.g., maple, for the maple host form) and to grow and develop best on them. These host forms have thus divergently adapted to their respective host plants. The project asks three major questions: First, does the relative availability of a native host plant influence the frequency with which its associated host form mates with beetles of other host forms? That is, does this aspect of the ecological context in which host forms find themselves influence the likelihood that they will diverge into separate species? Second, what particular reproductive barriers are most important in determining the degree to which two host forms do or do not interbreed? Do different host forms mate at different times or on different plants, or do they fail to survive on alternative hosts so that no mating between them occurs at all? Third, to what degree do the average tendencies of each host form mask biologically important variation among individual beetles in the behaviors that determine which host plant is preferred and whether or not a foreign mate is accepted? Each of these questions gets at critical outstanding issues about how and to what degree ecological factors contribute to the process of speciation and the production of biodiversity. Part of this research will be integrated with a lecture course at Vanderbilt University, with undergraduates collecting and analyzing data that is relevant to the topics being covered in class. Undergraduates will also more actively participate through enrollment in dedicated research courses. In the past, more than half of the students who have conducted research in this lab have been women. By examining the consequences of changing ecological context for habitat use and interbreeding between populations, this project will promote understanding of how widespread human impact on the ecological context experienced by organisms may affect biodiversity. By evaluating the behaviors that determine host plant selection, this work will help us to understand factors that promote the adoption of new host plants, as in the case of agricultural pests.
