Abstract
BackgroundTuning of the olfactory system of male moths to conspecific female sex pheromones is crucial for correct species recognition; however, little is known about the genetic changes that drive speciation in this system. Moths of the genus Ostrinia are good models to elucidate this question, since significant differences in pheromone blends are observed within and among species. Odorant receptors (ORs) play a critical role in recognition of female sex pheromones; eight types of OR genes expressed in male antennae were previously reported in Ostrinia moths.Methodology/Principal FindingsWe screened an O. nubilalis bacterial artificial chromosome (BAC) library by PCR, and constructed three contigs from isolated clones containing the reported OR genes. Fluorescence in situ hybridization (FISH) analysis using these clones as probes demonstrated that the largest contig, which contained eight OR genes, was located on the Z chromosome; two others harboring two and one OR genes were found on two autosomes. Sequence determination of BAC clones revealed the Z-linked OR genes were closely related and tandemly arrayed; moreover, four of them shared 181-bp direct repeats spanning exon 7 and intron 7.Conclusions/SignificanceThis is the first report of tandemly arrayed sex pheromone receptor genes in Lepidoptera. The localization of an OR gene cluster on the Z chromosome agrees with previous findings for a Z-linked locus responsible for O. nubilalis male behavioral response to sex pheromone. The 181-bp direct repeats might enhance gene duplications by unequal crossovers. An autosomal locus responsible for male response to sex pheromone in Heliothis virescens and H. subflexa was recently reported to contain at least four OR genes. Taken together, these findings support the hypothesis that generation of additional copies of OR genes can increase the potential for male moths to acquire altered specificity for pheromone components, and accordingly, facilitate differentiation of sex pheromones.
Highlights
Evolution of genes responsible for sex pheromone communication in moths is an attractive model for investigating the relationship between the divergence of genes and mechanisms of speciation
We have shown that transcription of mRNA from these desaturase genes occurs species [16], which might be under the control of an autosomal locus responsible for the difference in pheromone blend
Since we had started the screening before determining cDNA sequences of the O. nubilalis Odorant receptors (ORs) genes, we used the O. scapulalis OR genes for designing primers
Summary
Evolution of genes responsible for sex pheromone communication in moths is an attractive model for investigating the relationship between the divergence of genes and mechanisms of speciation. Release of sex pheromones from female moths is believed to play a critical role in species recognition [1,2]. An important question is how the pheromone recognition system in males can adapt rapidly to the changes that have occurred in the female pheromone biosynthetic pathway. Tuning of the olfactory system of male moths to conspecific female sex pheromones is crucial for correct species recognition; little is known about the genetic changes that drive speciation in this system. Moths of the genus Ostrinia are good models to elucidate this question, since significant differences in pheromone blends are observed within and among species. Odorant receptors (ORs) play a critical role in recognition of female sex pheromones; eight types of OR genes expressed in male antennae were previously reported in Ostrinia moths
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