Molecular aspects of pheromone evolution in moths

Abstract:
Moths rely on the sense of smell (olfaction) as the main sensory input system in search for potential food sources and in selection of suitable females by males. Specific pheromones are fundamental to the reproductive isolation of species and consequently the olfactory system of moths has evolved to a high level of sensitivity and specificity. This thesis investigates differences between two pheromone types found in geometrid and noctuid moths. These two pheromone types are based on olefinic acetate and polyenic hydrocarbon pheromone components that differ in biosynthesis. Olefinic acetates are biosynthesised from palmitic acid while the polyenic hydrocarbon pheromone components are biosynthesised from linoleic or linolenic acid. To examine the evolution of these pheromone types within the geometrid moth family I constructed a phylogenetic tree based on 'neutral' genes. The combination of the phylogenetic tree with current knowledge about the two pheromone types, revealed that subfamilies within the geometrids have changed at least twice from one pheromone type to another. In addition, I examined if species that use different pheromone components also differ in their pheromone binding proteins (PBPs). Pheromone-binding proteins are soluble proteins, which increase the capture and the solubilization of pheromone molecules in the lymph surrounding the olfactory receptors. PBPs have been identified for several species of moths, among which also noctuid species. The Noctuid PBPs that identified so far, are divided into two groups, a conserved and a more variable group. These different PBP groups originate from gene duplication; the genes encoding PBPs in Agrotis ipsilon and Agrotis segetum all comprise three exons and two introns but differ in length, mostly in intron 2. It has been hypothesised that the differences between PBPs from the two groups and between PBPs from different species were related to their pheromone system. Species using the same main pheromone components could have similar PBPs. Phylogenetic analysis of all known PBPs supported this hypothesis for the noctuid PBPs that use olefinic acetate pheromone components. For this reason, I therefore attempted to identify PBPs for the geometrids Idaea aversata and Bupalus piniaria, and the closely related drepanid Cilix glaucata, which represent both the olefinic acetate and the polyenic hydrocarbon pheromone types. From partial sequences I found that these PBPs belong to the non-noctuid group of PBPs that show high similarity when the species are closely related, regardless of the pheromone types they represent.