WHERE WOODRATS MEET: GENETIC, MORPHOLOGICAL, AND ECOLOGICAL DIFFERENTIATION AT THE BOUNDARIES BETWEEN SPECIES

Interactions between closely related species can have profound effects on genetic, morphological and ecological evolution. We have been studying species pairs in the genus Neotoma where lineages come into contact on the landscape. All of these pairs are far along the continuum towards speciation but still have the capacity to interbreed, creating narrow hybrid zones. Using various case studies, we highlight the type of interspecific interactions that characterize areas of contact between species of Neotoma, and how these interactions may have influenced the evolutionary trajectories of these lineages. We use two separate contact areas between Neotoma fuscipes and N. macrotis to highlight morphological and ecological patterns of character displacement in areas of transition between these species. We then further explore the underlying mechanisms that may operate in woodrat contact areas, by examining an area of contact between Neotoma lepida and Neotoma bryanti. In this latter system, we find that the species hybridize at our study site, but exhibit strong habitat segregation. Further, using both isotope and DNA analyses of diet, we show strong diet differentiation between the species and specialization within each taxon. The primary food plants used by each species are dominated by distinct plant secondary compounds whose detoxification likely require different metabolic specializations. Because of the potentially substantive metabolic challenge that would be experienced by individuals switching habitats and having to consume a novel diet, we suggest that the striking habitat segregation and minimal gene flow between the species at this site are at least partly the result of diet specialization. Ultimately, woodrats provide a rich system in which to study ecological adaptation and how interspecific interactions have contributed to diversification.