Exploring genomics of pheromone divergence in small Ermine moths

Moths evolved a thrilling mate-signalling system that entails a cascade of biosynthetic genes, with the encoded enzymes together establishing the final structure and ratio of each component in a pheromone mixture. Pheromone gland-specific acyl-CoA ∆11-desaturases evolved before the ditrysian radiation (1,2) and have been accredited as being key players in the catalysis of most long-chain unsaturated fatty acyl moieties described in moths to date. In rare cases however, moths rely only on saturated components to mediate mate-attraction. This is the case in Yponomeuta rorellus, one of the small Ermine moth species (Lepidoptera: Yponomeutidae) sympatrically distributed in west European Palaearctic regions. In contrast to its sister species that rely on a primary mixture of Z/E11-14:OAc (3), Y. rorellus differs dramatically in pheromone composition, having a simple bouquet composed of the saturated 14:OAc. This suggests that genetic or regulatory mechanisms have evolved that led to the loss of production of certain components. Our functional investigations on fatty-acyl- CoA reductases (FAR) in the group evidenced that in Y. rorellus, an active FAR with broad substrate range has maintained its ability to reduce unsaturated precursors in vitro, thereby strongly supporting that regulation occurs at an earlier stage in the biosynthesis. In order to validate the previously proposed biosynthetic scheme (3) and using a similar functional approach, we characterized and established the precise biochemical activity in vitro of two homologous ∆11-desaturases active in producing the respective ∆11-unsaturated intermediates in Y. padellus and Y. evonymellus. Using a GenomeWalker approach and a gene-specific primer walking strategy we screened genomic DNA libraries in Y. rorellus to query for a ∆11-desaturase like homolog gene and explore its putative adjacent 5´ promoter regulatory region. We aim at pin pointing genomic elements that could highlight the potential mechanistic causes implied in the observed genetic outbreak that led to its colonization of a new ecological niche through divergence in mate communication.