Socially polymorphic bees vary in genome-wide enhancer activity

Gene regulatory changes influence the evolution of many morphological traits, but their role in behavioral evolution is less clear. Comparative genomics studies of social insects suggest that changes in gene regulation are associated with evolutionary transitions in social behavior, but the activity of predicted regulatory regions has not been validated empirically. We used STARR-seq, a high-throughput enhancer discovery tool, to identify and measure the activity of enhancers in the socially polymorphic sweat bee, Lasioglossum albipes. This species shows variation in behavior across its range, including both social and solitary nests in different populations. Using STARR-seq on four populations of L. albipes, two social and two solitary, we identified over 40,000 enhancers in the L. albipes genome. These enhancers were located almost exclusively in non-coding regions of the genome, with strong enrichment for proximity to transcriptional start sites of genes and significant overlap with bioinformatically-predicted regulatory regions. 471 enhancers were differentially active between social and solitary populations of L. albipes, including enhancers proximal to genes enriched for presynaptic membrane functions. In addition, a subset of differentially active enhancers were proximal to genes near regulatory regions previously identified as experiencing selection in social vs. solitary lineages of sweat bees. Our preliminary data suggest that independent regulatory modifications are linked to a shared set of genes as part of a toolkit shaping both behavioral plasticity and behavioral evolution.