Comparing patterns of DNA methylation in two broadly distributed montane bumble bees

Understanding how spatial and environmental factors may shape evolution is a major question in biology. Here we present work evaluating differences in methylation in two broadly distributed montane bumble bees (Bombus vancouverensis Cresson and Bombus vosnesenskii Radoszkowski) across both the genome and landscape. They provide a useful juxtaposition between a species with narrower environmental requirements and a higher degree of population structure (B. vancouverensis) and one with flexible environmental requirements and a panmictic population structure (B. vosnesenskii). Comparison of these two species can yield insight into how different degrees of environmental specificity and population structure may alter how different variables influence molecular evolution. We find that both species are relatively similar at the genomic scale with very few (< 1%) CpG’s being methylation and most methylated CpG’s being found in gene bodies, particularly exons. At the landscape scale, both species were again similar with neither showing strong signals of spatial effects or population structure shaping patterns of variation in methylation. However, we do observe differences between the two species in terms of the effect of environmental variables on methylation patterns. B. vancouverensis had many more genes that had differentially methylated CpG’s related to the environment within them relative to B. vosnesenskii. We also observe overlap in genes with differentially methylated CpG’s and genes that were previously noted as containing environmentally associated outlier SNPs.