Urban land use limits regional bumble bee gene flow

Background/Question/Methods

Potential declines in native pollinator communities and increased reliance on pollinator-dependent crops have raised concerns about native pollinator conservation and dispersal across human-altered landscapes.  Bumble bees are one of the the most effective native pollinators and are often the first to be extirpated in human-altered habitats, yet little is known about how bumble bees move across fine spatial scales and what landscapes promote or limit their gene flow.  In this study, we examine regional genetic differentiation and fine-scale relatedness patterns of the yellow-faced bumble bee, Bombus vosnesenskii, across natural and human-altered landscapes to investigate how current and historic habitat composition impact gene flow. 

Results/Conclusions

We show that B. vosnesenskii exhibits low but significant levels of genetic differentiation across the study system (F_ST=0.019, D_est=0.049).  Most importantly, we reveal significant relationships between pairwise F_ST and resistance models created from contemporary land use maps.  Specifically, B. vosnesenskii gene flow is most limited by commercial, industrial, and transportation-related impervious cover.  Finally, our fine-scale analysis reveals that pair-wise relatedness declines significantly with increasing distance between individuals at the 1- 9km spatial scale, most likely due to local queen dispersal.  Overall, our results indicate that B. vosnesenskii exhibits considerable local dispersal and that regional gene flow is significantly limited by impervious cover associated with urbanization.