Abstract
Chemical signals are prevalent in sexual communication systems. Mate recognition has been extensively studied within the Lepidoptera, where the production and recognition of species-specific sex pheromone signals are typically the defining character. While the specific blend of compounds that makes up the sex pheromones of many species has been characterized, the molecular mechanisms underpinning the evolution of pheromone-based mate recognition systems remain largely unknown. We have focused on two sets of sibling species within the leafroller moth genera Ctenopseustis and Planotortrix that have rapidly evolved the use of distinct sex pheromone blends. The compounds within these blends differ almost exclusively in the relative position of double bonds that are introduced by desaturase enzymes. Of the six desaturase orthologs isolated from all four species, functional analyses in yeast and gene expression in pheromone glands implicate three in pheromone biosynthesis, two Δ9-desaturases, and a Δ10-desaturase, while the remaining three desaturases include a Δ6-desaturase, a terminal desaturase, and a non-functional desaturase. Comparative quantitative real-time PCR reveals that the Δ10-desaturase is differentially expressed in the pheromone glands of the two sets of sibling species, consistent with differences in the pheromone blend in both species pairs. In the pheromone glands of species that utilize (Z)-8-tetradecenyl acetate as sex pheromone component (Ctenopseustis obliquana and Planotortrix octo), the expression levels of the Δ10-desaturase are significantly higher than in the pheromone glands of their respective sibling species (C. herana and P. excessana). Our results demonstrate that interspecific sex pheromone differences are associated with differential regulation of the same desaturase gene in two genera of moths. We suggest that differential gene regulation among members of a multigene family may be an important mechanism of molecular innovation in sex pheromone evolution and speciation.
Highlights
Variation is the raw material of evolution; the nature of this variation remains a topic of much discussion amongst evolutionary biologists [1,2,3]
We have isolated six desaturases from two groups of sibling species of leafroller moths belonging to the genera Ctenopseustis and Planotortrix
Functional analyses in yeast and quantitative RT–Polymerase Chain Reaction (PCR) indicate that three of the desaturases are involved in the biosynthesis of sex pheromone components in these species
Summary
Variation is the raw material of evolution; the nature of this variation remains a topic of much discussion amongst evolutionary biologists [1,2,3]. The potential role in evolution of mutations that impact gene regulation rather than the amino acid sequence of a protein was initially proposed in the 1970s. King & Wilson [4] noticed that orthologous proteins between humans and chimpanzees were very similar at the amino acid level compared to the phenotypic differences between the two species and suggested that gene regulation could play an important role in explaining some of the phenotypic differences between the two primates. Since the relative importance in evolution of regulatory mutations (those affecting gene expression) versus structural mutations (those resulting in amino acid substitutions within the coding region of a protein) has been debated (e.g., Hoekstra and Coyne [1] and references therein). The relative importance of cis- versus trans-regulatory mutations in the course of evolution is predicted to be influenced by the degree of pleiotropy [5]
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