How does reproductive isolation evolve in sympatry?
Renewed interest in the role of ecology in speciation has resulted in many studies that support the hypothesis that adaptation and speciation are fundamentally linked. However, this field of research has developed little beyond simply establishing an association between adaptive divergence and speciation. One of the main goals of my research is to expand our understanding of ecology's role in speciation by empirically testing theoretical models on the ecological factors that promote  speciation with gene flow. To do this, I compare the strength of reproductive isolating barriers between sympatric red crossbill ecotypes under varying resource conditions throughout the Rocky Mountains. Consistent with theoretical work, my preliminary results suggest that reproductive isolation is highest when there is a direct coupling between the ecological conditions that promote divergence (e.g., feeding tradeoffs on alternative resources) and the timing of breeding. These results suggest a general explanation for why some lineages have speciated in the face of ongoing gene flow (e.g., Cassia crossbills and many host race insects), while others (e.g., most crossbill ecotypes and other bird species) have not.

Grouping behavior's role in speciation
Theory suggests that sympatric lineages can become reproductively isolated if phenotypically similar individuals form aggregations wherein mating occurs. Such "grouping" mechanisms automatically generate assortative mating with respect to the traits that mediate group formation. Classic examples of grouping mechanisms playing an important role in speciation include host plant choice in some herbivorous insects (e.g., Rhagoletis flies, Enchenopa treehoppers) and allochronic flowering in the palms of Lord Howe Island. I am currently exploring the importance of a neglected form of grouping (social grouping behavior) to speciation in the red crossbill complex. Crossbills are highly gregarious and feed in large flocks, where they use public information on flock mates' feeding rates to more efficiently assess resource quality. This promotes flocking behavior among phenotypically similar individuals that have similar feeding abilities on a given resource. Because crossbills choose mates from within flocks, such assortative flocking behavior leads to reproductive isolation between ecotypes and may have been key to the diversification of crossbill ecotypes. I am also exploring the role of social grouping behavior in speciation in a diversity of other taxa.

Cultural evolution, character displacement, and speciation
Biologists have long suggested that cultural evolution might be responsible for the extraordinary diversity of birds with learned songs (songbirds, hummingbirds, and parrots). However, direct evidence for cultural evolution's role in speciation has been extremely challenging to come by, and some evidence indicates that learned traits may impede rather than promote speciation. Using 20 years of audio recordings of banded Cassia crossbills, I found evidence for rapid character displacement in a learned trait (contact calls) between Cassia crossbills and red crossbill ecotypes that they co-occur with. Comparative analyses of call structure among other crossbills, playback experiments in the field, and previous genomic and paleobotanical studies all suggest that rapid evolution of contact calls may have been key to the rapid diversification and speciation of sympatric crossbills. This work suggests a novel mechanism by which cultural evolution can promote speciation with gene flow.

Undergraduate research
During my undergraduate degree at Michigan State University, I worked on several projects in Ian Dworkin's lab on experimental evolution of behavior and evolutionary genetics in Drosophila. While I no longer work on these topics/systems, working in this lab gave me a strong foundational understanding of a broad diversity of topics in evolutionary biology including quantitative genetics, behavioral ecology, and the study of phenotypic selection and adaptation. Several publications on this work can be found on my Google scholar page.