The evolution of sex pheromone composition in moths

Most moth species use female-produced pheromones to attract males for mating. The highly species-specific composition of moth sex pheromones is suggested to be driven by a need to reduce the risk of mis-mating and hybridisation between geographically overlapping, sympatric species. This need for species specificity is hypothesised to result in a high degree of stabilising selection on the pheromone blend within species, punctuated by large “saltational” shifts in pheromone composition at speciation events, resulting in a high diversity of pheromone blends across species. Current studies on sex pheromone evolution in moths have mainly been restricted to comparison between a small number of taxa, usually on the level of species or genus. Here I aimed to determine the impact of phylogeny and geography on the pheromonal differences between species across moths (Lepidoptera). I also aimed to determine the mode of evolution driving changes in pheromone difference between species at different taxonomic levels. Using a binomial GLM, I examined the relationship of phylogenetic and geographic distance to the pheromonal difference between 463 moth species. I found that phylogenetic distance had a strong positive correlation across the full dataset, however interactions with geographic distance were found to be non-significant. To determine the mode of evolution at different taxonomic levels, I also conducted a binomial GLM analysis on species within and between 14 genera for which information on multiple species were available. In contrast to the full dataset analysis, within-genera relationships between phylogeny and pheromone composition were found to be non-significant, with closely related species expressing as different pheromone blends as more distantly related species while still sharing common components. Based on the findings of this study, it is hypothesised that pheromonal distance is impacted by phylogeny at higher taxonomic levels, while still allowing for a conservative-saltational mode of evolution within genera.