Mountains as refugia: evidence from bumble bee brain transcriptomes

As anthropogenic change continues to impact global biodiversity, the importance of rapidly identifying biodiversity refugia cannot be overstated. In this study, we employed a molecular test of the hypothesis that mountains serve as refugia for bumble bees against anthropogenic stressors. To explore this hypothesis, we compared stress-related patterns of gene expression in the brains of wild, pollen-foraging bumble bees of two species, B. vosnesenskii and B. melanopygus, collected at different elevations throughout the Sierra Nevada Mountain range in California, USA. We found evidence that the expression of several immune and detoxification genes is associated with elevational differences. This suggests that bees are experiencing differential exposure to stressors along an elevational gradient, which is an important criterion for identifying refugia across dynamic and heterogenous environments. This study thus provides evidence that mountains may serve as refugia for bumble bees in response to anthropogenic stressors, as has been detected for many other organisms.