Meeting Abstract
Juvenile hormone (JH) has diverse functions in insects and is critical in the control of plastic phenotypes. It’s role in the condition-dependent expression of male beetle weapons is important but not well known. What is known is that JH mediates the condition dependent expression of mandibles in male stag beetles and male dimorphic horns of dung beetles. What remains unknown is how general this JH mediated response to condition is in sexually –selected traits in beetles and how JH interacts with other endocrine pathways to generate an appropriate environmental response. JH is part of a much larger endocrine feedback loop in which ecdysone represses JH. In dung beetles, ecdysone levels negatively correlate with adult horn length. In this study, we tested the hypothesis that JH induces the exaggeration of the elaborate head horns of the Asian rhinoceros beetle, Trypoxylus dichotomus. Unlike the stag beetle we found that ectopic application of fenoxycarb significantly delayed pupation time, but had no effect on adult horn size relative to body size. On the other hand, RNAi mediated knockdown of the juvenile hormone receptor Methoprene-tolerant (Met) decreased head horn size, relative to body size. In addition, we found no correlation between titers of ecdysone and adult horn length. Finally, RNAi mediated knockdown of the ecdysone receptor had no effect on adult horn scaling. Our results indicate that endocrine regulation of sexual dimorphisms in beetle weapons has evolved significantly between clades.
