|Lozier, Jeffrey -|
Submitted to: Conservation Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 18, 2013
Publication Date: May 26, 2013
Citation: Lozier, J., Strange, J.P., Koch, J. 2013. Landscape heterogeneity predicts gene flow in a widespread polymorphic bumble bee, Bombus bifarius (Hymentoptera: Apidae). Conservation Genetics. 14: 1-12. Interpretive Summary: In order to better understand the effects of habitat on the genetic structure of the Two-formed Bumble Bee, Bombus bifarius, we applied a new analysis method to an existing data set. Because bumble bees are important pollinators it is important to understand how their populations react and adapt to the landscape around them, especially in light of recent declines in the populations of several species in the United States. We first mapped the historic range of suitable habitats of the Two-formed Bumble Bee in the United States and southern Canada using data gathered from museum collections and climate data. Genetic data was derived from 447 individuals from 26 locations throughout the western US and Canada. We used circuit theory to demonstrate that the complex landscape of the western US, and thus the patchwork of suitable habitat that landscape creates, is important in influencing the genetic differences seen in this widespread species. These results can be applied to conservation efforts though increasing understanding of the role that habitat plays in the connection of bumble bee populations.
Technical Abstract: Bombus bifarius is a widespread bumble bee that occurs in montane regions of western North America. This species has several major color polymorphisms, and shows evidence of genetic structuring among regional populations. We test whether this structure is evidence for discrete gene flow barriers that might indicate recent reproductive isolation (among color forms, for example) or instead reflects clinal variation associated with spatially limited dispersal in a complex landscape. We use climate data and a comprehensive set of B. bifarius natural history collection records to model the spatial distribution of environmentally suitable habitat in western North America and predict pathways of potential gene flow using circuit theory to generate resistance distances between each pair of populations. Resistance distances that incorporate environmental suitability information predict patterns of genetic structure much better than pairwise geographic distances or Bayesian clustering alone. Results suggest that there are no intrinsic barriers to gene flow in B. bifarius, but that the distribution of suitable and unsuitable habitat at broad scales, largely associated with islands and variation in precipitation, limits dispersal sufficiently to result in population differentiation.