Mate recognition in orchid bees is mediated by acquired chemical signals

Abstract The evolution of prezygotic reproductive barriers plays a central role in speciation and is often mediated by divergence in mating signals. Male orchid bees collect volatile compounds from the environment to concoct species-specific perfumes that function as sexual chemical signals during courtship display. While perfumes are thought to convey species recognition, their direct role in assortative mating remains unresolved. Here, we experimentally tested whether perfume composition facilitates mate recognition between two recently diverged and sympatric sister species, Euglossa dilemma and E. viridissima. We collected perfumes from males in sympatric regions of Mexico and experimentally supplemented E. dilemma males with either conspecific (E. dilemma) or heterospecific (E. viridissima) perfumes. We conducted single-choice mating assays and found that the rate of male courtship display did not differ between treatments. However, females of E. dilemma exhibited a strong preference for males with conspecific perfumes. While 77% of males loaded with E. dilemma perfume mated, only 8% of males loaded with E. viridissima perfume mated. Our results support the hypothesis that perfume composition alone can mediate reproductive isolation in orchid bees. These findings highlight the role of environmentally acquired signals as extended phenotypes that can rapidly generate behavioral isolation and contribute to speciation.