Evolution of male sex pheromone composition and diversification of the butterfly genus Bicyclus

Understanding the speciation process usually involves the study of the geographic and ecological factors influencing reproductive isolation, as well as the action of evolutionary forces. Recently it was proposed that the type of communication channel, if it offers large possibilities in the direction of evolution of the signals, could help species to differentiate in a similar way as an ecosystem with empty ecological niches would. Olfactory communication could be such a modality since compared to other modes of communication, acoustic or visual, it benefits from a large variety of signals, thanks to the tremendous diversity of chemical compounds that can be used. In addition, the specificity of the olfactory receptors necessary to detect particular chemical compounds confers a strong privacy to the information transfer, regarding illicit receivers like predators. This thesis aimed at investigating the importance of olfactory sexual communication in the evolution of reproductive isolation in the butterfly genus Bicyclus. We first compared the composition of putative male sex pheromone (pMSP) across 32 species in a phylogenetic perspective. We observed that pMSP composition was very diverse, species specific, rapidly evolving, and that stronger differences of composition likely allow species to recognise each other when sharing the same ecosystem. In a second time, we investigated the diversity of the pMSP within species and discovered similar differences as between species. This supports the hypothesis that pMSP diversification can predate speciation and can therefore be a cause of this enigmatic process. Overall, our results strongly suggest that the evolution of male sex pheromone is involved in speciation in the Bicyclus genus, and support the hypothesis that olfactory communication allows a large diversity of signals, evolving without obvious constraint, and which could rapidly lead to reproductive isolation.
(SC - Sciences) -- UCL, 2015