Mountains as refugia: evidence from bumble bee brain transcriptomes

Background/Question/Methods

Anthropogenic drivers, including climate change and land-use intensification, are a key driver of species declines. It is hypothesized that for species that live in both montane and low elevation areas, areas that are higher in elevation can serve as a refuge against anthropogenic drivers. Here, we tested this hypothesis using bumble bees as a model. Many bumble bee species have been shifting to higher elevations and latitudes in response to climate change and habitat loss. Specifically, we hypothesized that mountains serve as a refuge for bumble bees against anthropogenic stressors, such as changes in climate and the release of toxic chemicals (e.g., pesticides) into their nesting and foraging habitats. To explore this hypothesis, we examined patterns of gene expression in the brains of wild, pollen-foraging bumble bees of two species (B. vosnesenskii, B. melanopygus) collected at different elevations in the Sierra Nevada, as well as different distances from the Central Valley, a highly disturbed agricultural landscape in Central California.

Results/Conclusions

We identified 12,925 expressed genes in our dataset. Broadly, global gene expression strongly differed between the two species, but we did not observe strong differences in global patterns between bees collected at different elevations or distances to the Central Valley. When we filtered genes to stress related genes however, we found differences in gene expression based on elevation for some genes. This suggests that elevation may buffer bumble bees again anthropogenic drivers.