The perception of chemicals in the environment is a principal way in which many animals gain information from their surroundings. How an animal behaviorally responds to these signals may affect their reproductive success. An example of this is the preference insects have for distinct plants they feed on, based on the chemical compounds emitted from these plants. Specifically, changes in their preferences for chemical signals through changes in their ability to perceive them using their sense of smell (olfaction) can contribute to divergence among populations and species formation. This study will examine the evolution of the olfactory system within a single species, in the context of differences in chemical cues across its geographical range. This knowledge is fundamental to understanding more broadly how genetic and neural variation can result in fundamental differences in behavior. Results from the proposed work will thus document mechanisms by which a species emerges. It will also have broad implications for applied agriculture. Many herbivorous insects locate food and mates using their sense of smell, resulting in adverse effects on agricultural productivity. In summary, in addition to advancing the understanding of olfaction, this research will serve as a model for understanding the mechanisms underlying divergence in behavior and ecological speciation. Moreover, its integrative nature makes it ideally suited for training students, since it uses behavioral, molecular genetic, and neurophysiological approaches. Outreach activities will include exposing high school students to research through hands-on experiential learning that highlights results from the proposed research and, more broadly, concepts in sensory biology and evolution.
Understanding species formation ideally includes examination of the process prior to its completion. Four geographically distinct populations of the fly Drosophila mojavensis currently exploit four different cactus species that emit specific combinations of volatile chemical compounds that are primary cues for plant identification. The objective of this proposal is to determine the correspondence between variation in olfactory cues, olfactory sensitivity, and behavioral preference for natural odorants. The specific aims are to compare populations of the same species that use different host plants: (1) neurophysiological responses to host plant-specific volatiles, (2) molecular genetic mechanisms underlying different neurophysiological responses, and (3) to determine whether the volatiles eliciting different neurophysiological responses translate into behavioral discrimination. These studies will result in further understanding of how the peripheral nervous system can change in response to changing ecological environments, and how these changes may contribute to population divergence.
