Evolution of odorant receptor (OR) genes in perfume-making orchid bees

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Male orchid bees collect and accumulate complex and species-specific mixtures of volatile chemicals (perfumes), which they harvest from various sources in their environment and later expose during courtship, presumably to communicate male identity (species) and/or quality (fitness) to conspecific females. This communication system is unique among insects in that the acquisition of the male sex trait (perfume) and the female preference for it are simultaneously controlled by the chemosensory system, i.e. are linked through the gene families encoding olfactory sensitivity. This genetic linkage creates unexplored opportunities for coevolution of male trait and female preference, and may facilitate perfume-driven reproductive isolation and speciation. Here, we propose to (1) compare odorant receptor (OR) genes and OR gene expression in the antennae of two recently diverged sibling species of Euglossa, (2) functionally characterize diverged OR genes that are under positive directional selection, (3) explore the phylogeography of these OR genes and corresponding perfume phenotypes in Central America, and (4) compare OR gene expression in the antennae of male and female bees to test for sex-specific olfactory architectures. This sensory-based project complements ongoing chemistry-based research on perfume differentiation, and will enhance our understanding of the evolution of this specialized communication system.