Down syndrome cell adhesion molecule 1 evolution and its relationship to sociality: hymenopteran Down syndrome cell adhesion molecule 1 exhibits accelerated evolution in variable exon regions

Abstract Down Syndrome Cell Adhesion Molecules (DSCAM) are transmembrane domain proteins belonging to the immunoglobulin superfamily and are expressed during brain development. While present in many other organisms, DSCAM has gone through multiple independent duplication events in arthropods and can form over 10,000 different isoforms through alternative splicing. Due to DSCAM’s role in brain development and immune system functions, we investigated the relationship of DSCAM1 evolution to the evolution of sociality in arthropods. To assess structural variation, we examined phylogenetic trees derived from variable exons against the full DSCAM1 gene tree. Additionally, we performed likelihood ratio tests to identify regions undergoing evolutionary conservation or acceleration. Our findings reveal evidence of evolutionary acceleration in DSCAM1 within Hymenoptera, particularly in exons 4, 5, and 6, which correspond to the second and third immunoglobulin domains. Interestingly, this acceleration occurs regardless of social structure in bees and wasps. Accelerated evolution in these regions could have significant implications for neural circuit development in Hymenoptera, as these variable regions are responsible for generating diverse protein isoforms. This pattern of accelerated evolution potentially suggests that Hymenoptera have developed more complex neural circuits or undergone substantial changes in neuronal wiring.