Evolutionary mechanisms of pheromone divergence in moths and butterflies
In order to coexist, biological species need to be reproductively isolated and the evolution of mechanisms ensuring efficient reproductive isolation barriers is an integrated part of the speciation process. The evolution of mechanisms involved in specific mate finding and mate choice may account for premating reproductive isolation. In the Lepidoptera, with the exception of butterflies, mate finding is primarily mediated by female-emitted sex pheromones and finely tuned male responses. Pheromone changes can drive species divergence and may account for many instances of successful speciation. An intriguing question in the evolution of sexual communication is how signal and response are coordinated for mate recognition (and species specificity) and how signal and response may still change under speciation.
The purpose of this research programme is to link molecular insight about the genetic and biochemical mechanisms underpinning the evolution of novel pheromones with ecological and evolutionary theories concerning the role of pheromones in reproductive isolation and speciation. Using molecular and genomic tools, functional assays and phylogenetic analysis we explore the gene families that control this system. We are particularly interested in unravelling the mechanisms - including gene duplications, point mutations and regulation of transcription - that allow the diverging sex pheromone systems to escape the stabilizing selection ruling under normal conditions.
Ongoing studies focus on several groups of moths, butterflies of the genus Bicyclus as well as caddisflies, the sister group of Lepidoptera. In vitroexpression systems have allowed us to confirm the functional identities of many moth desaturases and reductases characterized from pheromone glands and involved in pheromone production. On the reception side, the antenna is the primary olfactory appendage in insects. Male antennae are morphologically distinct from those of females and contain various types of sensilla housing olfactory receptors, also encoded by a multigene family, and some of which are specifically tuned to interpret the species-specific pheromone stimuli.
Phylogenetic analysis has revealed that new types of pheromone components have evolved at least twice in the evolution of the Lepidoptera. At the same time, female-produced pheromones were apparently lost at least once in the evolution of the day-active butterflies, which rely on visual cues for mate finding. Male-produced pheromones may mediate courtship in butterflies as well as moths. Moths and butterflies provide an excellent model for studies of the causes and consequences of mate signal-response divergence and the diversification of a sophisticated mate communication system.