Gene networks reveal alternate routes to mimetic coloration in North American bumble bees

Bumble bees have captivated researchers from various disciplines due to their unique physiological, morphological, and behavioral characteristics. Among these traits, coloration and patterns have garnered significant interest from evolutionary biologists, particularly because the numerous convergent mimicry complexes observed globally present opportunities to understand evolutionary genetic principles using natural replication. North America alone hosts three such convergent complexes encompassing over 46 bumble bee species. The recurring phenotypes among different species provide a great opportunity to explore their evolutionary genetics, key genes in their coloration, and the evolutionary history of their gene networks. In this study, we utilize transcriptomic data from black and red color morphs of several bumble bee species at various developmental stages, focusing on abdominal epidermal tissues linked to their respective mimicry complexes. By employing cross-developmental transcriptomics, we analyze their gene networks and trace the evolution of color and pigmentation-related gene networks, to shed light on the key molecular players across several species. Our findings support the involvement of core gene pathways targeting similar upstream developmental genes and shared downstream pigmentation genes, but also species-specific genes, suggesting that these species achieve similar phenotypes through partially distinct genetic pathways. Utilizing their phylogeny, we were able to track the evolution of these gene networks relative to phenotypic transitions and thus gain deeper understanding of the genetic mechanisms underlying their diverse coloration patterns.