Identification of ecdysteroids and ecdysteroidogenic genes in dragonflies and damselflies

Ecdysteroids are critical in regulating biological processes such as ecdysis, metamorphosis, embryogenesis, and reproduction in insects. Nevertheless, the ecdysteroid repertoire and expression patterns of their synthesis genes in Odonata (dragonflies and damselflies), which belong to the most-ancestral winged insect group, have remained elusive. In this study, we examined the ecdysteroid profile of eight Odonata species and the ecdysteroid fluctuation during metamorphosis in the damselfly Ischnura senegalensis (Zygoptera, Coenagionidae) and the dragonfly Pseudothemis zonata (Anisoptera, Libellulidae). We found that ecdysone and 20-hydroxyecdysone (20E) titers corresponded to the progression of ecdysis in the penultimate nymphal instar and metamorphosis in the final nymphal instar, whereas 7-dehydrocholesterol was consistently present in the hemolymph of all the examined species and developmental stages. Considering that a higher amount of 20E was detected than ecdysone, 20E is important for inducing ecdysis and metamorphosis in Odonata, like other insects. We also confirmed that the majority of ecdysteroidogenic genes were conserved in Odonata, and their stage- and region-specific expression patterns were examined in I. senegalensis and P. zonata. Unexpectedly, most ecdysteroidogenic genes were expressed in a variety of tissues. Our study provides insights into the evolution and diversification of the ecdysteroidogenic pathway among insects.