TY - JOUR T1 - The evolutionary dynamics of the odorant receptor gene family in corbiculate bees JF - bioRxiv DO - 10.1101/130781 SP - 130781 AU - Philipp Brand AU - Santiago R. Ramírez Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/04/26/130781.abstract N2 - Insects rely on chemical information to locate food, choose mates, and detect potential predators. It has been hypothesized that adaptive changes of the olfactory system facilitated the specialization and diversification of numerous insect lineages. In fact, modifications of life history strategies often occur in parallel with evolutionary changes in Odorant Receptor (OR) genes. However, the molecular mechanisms underlying the evolution of insect OR genes remain poorly understood. Corbiculate bees include economically and ecologically important bee pollinators that exhibit varying degrees of social organization, diverse sex pheromone systems, and manifold associations with floral resources. We investigated the molecular mechanisms governing the evolution of the OR gene family in corbiculate bees. Our results indicate that the genomic organization of the OR gene family has remained highly conserved for approximately 80 million years, despite exhibiting major changes in repertoire size among bee lineages. Moreover, the evolution of OR genes appears to be driven by lineage-specific gene duplications in few genomic regions harboring large numbers of OR genes. A selection analysis revealed that OR genes evolve under positive selection, with the strongest signals detected in recently duplicated copies. Our results indicate that chromosomal translocations had a minimal impact on OR evolution, and instead show that local molecular mechanisms drive OR repertoire size. Our results provide empirical support to the longstanding hypothesis that positive selection shaped the diversification of the OR gene family. Our results shed new light on the molecular mechanisms underlying the evolution of olfaction in insects and gene families in general.Significance Statement Despite playing a central role in the diversification of insect lineages, the evolution of insect olfactory systems remains poorly understood. Here, we analyze the Odorant Receptor (OR) repertoire across the corbiculate bees—a lineage of important insect pollinators—to test the hypothesis that genomic re-organization and positive selection shaped the evolution of the OR gene family. We show that locally acting molecular mechanisms are the driving force of OR gene family evolution in corbiculate bees. Moreover, we provide empirical support for the longstanding hypothesis that positive selection impacts the evolution of recently duplicated insect OR genes. Our results augment our understanding of the molecular mechanisms that govern the evolution of olfactory systems in insects and gene families in general. ER -