Involvement of the doublesex gene in body color masculinization of the blue-tailed damselfly, Ischnura senegalensis

Abstract

Odonata (dragonflies and damselflies) display remarkable color pattern diversity including sexual dimorphism and intrasexual polymorphism. We previously found that expression of a sex-determining transcription factor, the doublesex (dsx) gene, is associated with female color polymorphism (gynomorph for female-specific color and andromorph for male mimicking color) in the blue-tailed damselfly, Ischnura senegalensis. Here we investigate the function of dsx gene on thoracic coloration by electroporation-mediated RNA interference (RNAi). RNAi of the dsx common region changed color patterns of males and andromorphic females to patterns of gynomorphic females. Further, gynomorphic color pattern was not affected by dsx RNAi. The long isoform of dsx RNAi produced no effects, suggesting that the short isoform of dsx is important for body color masculinization in both males and andromorphic females. Expression pattern changes were also examined in five genes with different expression levels between sexes and female morphs. Among these genes are two melanin suppressing genes, black and ebony, that were upregulated in the dsx-RNAi region compared to a control region. Upregulation coincides with a gynomorphic orange color instead of the black stripe observed in males and andromorphic females. dsx may regulate male color differentiation by suppressing black and ebony in the thoracic region of I. senegalensis. Results add to the understanding of molecular mechanisms underlying the evolution of female polymorphism in Odonata.