Allelic variation in a fatty-acyl reductase gene causes divergence in moth sex pheromones

Abstract

Pheromone-based behaviours are crucial in animals from insects to mammals, and reproductive isolation is often based on pheromone differences. However, the genetic mechanisms by which pheromone signals change during the evolution of new species are largely unknown. In the sexual communication system of moths (Insecta: Lepidoptera), females emit a species-specific pheromone blend that attracts males over long distances. The European corn borer, Ostrinia nubilalis, consists of two sex pheromone races, Z and E, that use different ratios of the cis and trans isomers of acetate pheromone components. This subtle difference leads to strong reproductive isolation in the field between the two races, which could represent a first step in speciation. Female sex pheromone production and male behavioural response are under the control of different major genes, but the identity of these genes is unknown. Here we show that allelic variation in a fatty-acyl reductase gene essential for pheromone biosynthesis accounts for the phenotypic variation in female pheromone production, leading to race-specific signals. Both the cis and trans isomers of the pheromone precursors are produced by both races, but the precursors are differentially reduced to yield opposite ratios in the final pheromone blend as a result of the substrate specificity of the enzymes encoded by the Z and E alleles. This is the first functional characterization of a gene contributing to intraspecific behavioural reproductive isolation in moths, highlighting the importance of evolutionary diversification in a lepidopteran-specific family of reductases. Accumulation of substitutions in the coding region of a single biosynthetic enzyme can produce pheromone differences resulting in reproductive isolation, with speciation as a potential end result.

From Russia with lobe: genetic differentiation in trilobed uncus Ostrinia spp. follows food plant, not hairy legs

“…It includes genes affecting post-diapause development time (Pdd: Glover et al, 1992;Dopman et al, 2005Dopman et al, , 2010, male behavioural response to different female sex pheromones (Resp: Glover et al, 1990;Dopman et al, 2004Dopman et al, , 2005Dopman et al, , 2010, differential success rate in larval development on either host plant (Calcagno et al, 2007) and/or other genes located in the vicinity of Tpi (Bourguet et al, 2000;Martel et al, 2003;Bontemps et al, 2004;Dopman et al, 2004Dopman et al, , 2005. The second set of candidates is autosomal and includes genes responsible for differences in female sex pheromones (Pher: Roelofs et al, 1987;Dopman et al, 2004Dopman et al, , 2010Lassance et al, 2010), an unidentified close-range mechanism ensuring assortative mating in laboratory settings (AssMat: Pélozuelo et al, 2007) and/or other genes located in the vicinity of Mpi (Bourguet et al, 2000;Martel et al, 2003;Bontemps et al, 2004).…”

A recombination suppressor contributes to ecological speciation in OSTRINIA moths

“…Z-strain females produce a 3:97 ratio of E/Z11-14:OAc, whereas E-strain females use a 99:1 ratio. Strain identities of all parental stocks were confirmed by genotyping pgFAR, the autosomal locus that determines the female sex-pheromone blend (Lassance et al, 2010;Supplementary Table S1).…”

Beyond species recognition: somatic state affects long-distance sex pheromone communication

“…Since 1959, when the first long-range sex pheromone was chemically characterized by Butenandt et al [12], long-distance pheromone communication has been subjected to substantial research, capturing the attention of ecologists, evolutionary biologists, biochemists, neurophysiologists and molecular biologists (e.g. [13][14][15]). Long-range sex pheromones, which are usually composed of few components, have been assumed to serve solely as species recognition signals and therefore, to be subjected to a high degree of stabilizing selection (e.g.…”