The use of pinned specimens helps uncover patterns of genetic differentiation and signatures of selection in a wild pollinator

Determining the impact of ecological processes on adaptive genetic variation in wild populations can aid in evaluating the resilience potential in species of conservation concern. However, an in-depth understanding of gene-environment interactions to uncover patterns of global biodiversity losses requires inclusion of non-model taxa in genomic studies. For insects, this goal can be achieved by the use of pinned specimens from curated collections. In this study, we employ pinned specimens to infer the population structure and test for evidence of adaptive divergence in a native North American wild bee, Agapostemon virescens. We compare samples across three collections methods (pan trap, sweep net, blue vane) and verify the utility of pinned specimens in population genetics studies, while at the same time providing insights into the local adaptation patterns of a ground-nesting pollinator. Genome-wide single nucleotide polymorphism (SNP, n = 30,829) data revealed that A. virescens in eastern Canada is comprised of one genetic cluster, with low levels of differentiation between regions. Furthermore, A. virescens in each of the four examined regions had low heterozygosity and exhibited significant levels of inbreeding. By examining signatures of selection associated with genetic structure and environmental variation, we identified outlier SNPs corresponding to genes involved in energy metabolism, pathogen response and insecticide resistance. Combined, these findings help characterize the population structure, genetic diversity and adaptive variation of a wild pollinator species and enhance our understanding of general local adaptation patterns in ground-nesting bees.