The effect of thedoublesexgene in body colour masculinization of the damselflyIschnura senegalensis

Odonata species display a remarkable diversity of colour patterns, including intrasexual polymorphisms. In the damselfly (Ischnura senegalensis ), the expression of a sex-determining transcription factor, thedoublesex (Isdsx ) gene is reportedly associated with female colour polymorphism (CP) (gynomorph for female-specific colour and andromorph for male-mimicking colour). Here, the function ofIsdsx in thoracic coloration was investigated by electroporation-mediated RNA interference (RNAi). RNAi of theIsdsx common region in males and andromorphic females reduced melanization and thus changed the colour pattern into that of gynomorphic females, while the gynomorphic colour pattern was not affected. By contrast, RNAi against theIsdsx long isoform produced no changes, suggesting that theIsdsx short isoform is important for body colour masculinization in both males and andromorphic females. When examining the expression levels of five genes with differences between sexes and female morphs, two melanin-suppressing genes,black andebony , were expressed at higher levels in theIsdsx RNAi body area than a control area. Therefore, theIsdsx short isoform may induce thoracic colour differentiation by suppressingblack andebony , thereby generating female CP inI. senegalensis. These findings contribute to the understanding of the molecular and evolutionary mechanisms underlying female CP in Odonata.