Chemically mediated sexual signals restrict hybrid speciation in a flea beetle

The evolution of reproductive isolation following hybridization is a major obstacle that may limit the prevalence of hybrid speciation among specific groups of organisms. Here, we use a flea beetle system to offer a behavioral hypothesis for why there are so few examples of homoploid hybrid speciation among insects. Specifically, we examined cuticular hydrocarbon (CHC) mating signals and mate-choice decisions of Altica fragariae and A. viridicyanea to test whether the signals produced by hybrids cause prezygotic reproductive isolation. Although hybrids of A. fragariae and A. viridicyanea had unique CHC profiles as compared to the parental species, mate-choice trials indicated that these differences were insufficient to prevent gene flow between hybrids and parental species. We found that mate-choice decisions and CHC signals were not correlated. Considering the ubiquity of CHC signaling molecules in insects, we propose that decoupling of CHC signals and mate choice may be a general mechanism limiting hybrid speciation in insects.