Evolution of mate signalling in moths: biosynthetic gene families and pheromone diversification

Pheromones are intraspecific chemical signals serving as a ubiquitous form of communication, particularly among insects. Female sex-pheromone signals act as the core constituent in the specialized odour-mediated moth mate-recognition system. Female moths typically release multicomponent mixtures of alcohols, aldehydes or acetates. The biosynthetic machinery controlling pheromone production comprises a handful of enzymes, yet the combination assortment generates a remarkable variety of compounds. Pheromone specificity is closely associated with the evolution of reproductive isolation and the divergence of moth species. Using a combination of biochemical, molecular, genetic and phylogenetic tools, I have attempted to discern how pheromone biosynthesis is achieved at the molecular level, how the chemical and structural variation arose and what the proximate genetic transitions that underlie phenotypic novelties are. A special regard was given to (i) characterizing fatty-acyl-CoA desaturase and reductase pheromone gland cDNA transcripts; (ii) setting up a yeast-based heterologous expression system capable of handling expression of both types of enzymes; (iii) determining the enzymes functions; (iv) reconstructing biosynthetic pathways; (v) inferring the genes’ evolutionary histories; and (vi) linking structural genetic changes to protein functionality. Insights from studies of a primitive Prodoxidae species uncovered that a gene duplication gave rise to a Lepidoptera-specific ∆11-desaturase clade close to the time of divergence between basal and advanced moth families, an event which was certainly favourable to the establishment of the ditrysian pheromone chemistry. Strong empirical data showed that the functional properties of extant ∆11-desaturase orthologues contribute extensively to the remarkable structural diversity found in advanced moth families. I also identified a rare instance of neofunctionalization in an ancestral desaturase lineage and the first ∆6-desaturase functioning in mating communication in insects. I demonstrated that the reduction step in yponomeutids is accounted for by a single reductase (pgFAR), exhibiting a broad range of activity and belonging to a Lepidoptera-specific gene subfamily. pgFARs play an important role in adjusting the pheromone ratio and are emerging as a pivot of the diversification of moth sexual signals. Finally, a causal mutation responsible for a shift in substrate preference between two Ostrinia spp. pgFARs (Crambidae), was identified, which substantiate the theory that pheromone evolution proceeds through both gradual and abrupt mutational shifts.