A population genomic analysis of a widespread North American bumble bee, Bombus huntii

Bumble bees (genus Bombus) are ecologically and agriculturally important pollinators. As many bumble bee species face declining populations, it is increasingly important to obtain a greater understanding of phylogeography and taxonomy to identify species of concern. Bombus huntii is a widespread North American bumble bee, ranging from Canada to southern Mexico. A previous study using microsatellites identified population structure between B. huntii populations in the northern (U.S. and Canada) and southern parts of the range (Mexico). Here, we utilized the chromosome-level B. huntii genome assembly and whole-genome resequencing to re-analyze populations from the previous microsatellite study to better understand the population genetic history of the species. We aimed to determine if the southern (Mexico) populations of B. huntii warrant classification as a separate species from the northern (U.S. and Canada) populations. We tested for the presence of population structure and constructed a whole-genome phylogeny. We also evaluated patterns of genetic diversity at multiple scales. We found that genetic divergence is smaller than other recently separated bumblebees, which, together with some evidence of gene flow provides a lack of strong support for considering the two populations as distinct species.