My lab uses molecular genetic markers to study ecological and evolutionary processes in populations of wild organisms. Many of the basic questions in ecology and evolution tie into the fundamental problem of what limits the movement of individuals and the genes they carry at various spatial and temporal scales. Population genetics provides tools to investigate the distribution of genetic variation within and between species to answer questions such as how species form, how novel phenotypes arise, how organisms adapt to variation in their environments, and how landscape heterogeneity structures populations. My lab primarily uses genome sequencing data (e.g., RADseq, transcriptomes, and whole genome resequencing) to investigate adaptation and demography, and we integrate diverse tools to supplement molecular methods, including field surveys, GIS, and natural history collections. I highlight a few projects below, but for detailed information see my webpage.

Bee diversity, decline, and population genetics

Pollinator decline is recognized as a major problem globally. My colleagues and I have conducted large-scale intensive surveys of bumble bee (Bombus) populations throughout the U.S. and identified that several once widespread species have undergone serious reductions in range and abundance. Likely factors in these declines include habitat loss and fragmentation, as well as the introduction of novel disease agents. We determined that the declining species are much more likely to host infections of Nosema bombi, a widespread Microsporidian parasite common in Europe, lending support for the disease hypothesis. We have recently employed novel genetic tools to natural history collection specimens to test whether N. bombi in North America is likely to be invasive from Europe.

We have also investigated population genetics of six species, and identified that genetic diversity in declining bumble bees is lower than in their healthy relatives, which could provide another possible factor in their declines. Genome-wide analyses using RADseq data suggests this pattern may be much more complex and in need of further study.

Gene flow in all species appears high at large geographic scales, however, suggesting that dispersal is not severely limited. Our current work uses comparative population genomics to test hypotheses about adaptation of bumble bee species to challenging environments, and ways to predict the future effects of habitat fragmentation on historically well-connected populations. We do much of this work in mountains of the western US, where we use extreme niche differences across elevations to determine the evolutionary forces shaping intraspecific variation.

Speciation and phenotypic divergence

A fundamental question in evolution is “How do new species arise?” One of my interests is the use of closely related populations or species to better understand the factors that contribute to reproductive isolation of lineages, as well as the extent to which hybridization may occur after divergence. One system in which we’ve recently focused involves bumble bees with different color patterns in the Bombus bifarius species group. We are using large scale genomic data sets to determine genetic differences driving color pattern differences and the degree of reproductive isolation among populations. We have recently discovered a gene that shows strong signatures of divergent selection between color morphs, representing some of the first evidence for a genetic mechanism involved in bumble bee pigment polymorphism. This work also integrates GIS-based approaches with population genetics to investigate potential mechanisms driving speciation.