Juvenile hormone action inducing neotenic differentiation in the damp-wood termite
Kohei Oguchi, Kohei Oguchi , Toru Miura
Department of Biological Science, University of Tokyo, Japan; Department of Biological Science, University of Tokyo, Japan ; Department of Biological Science, University of Tokyo, Japan
Termite castes exhibit distinctive morphologies specialized in colony tasks. In basal termite species, working immaturestermed “pseudergates” differentiate into castes depending on extrinsic factors such as social interactions. Whenreproductives in a colony die, pseudergates differentiate into supplementary or replacement reproductives calledneotenics. Despite juvenile morphological characteristics, neotenics develop reproductive organs and genital structures asprimary reproductives. Juvenile hormone (JH) is known to be responsible for the caste differentiation in termites, althoughthe patterns of JH titer and downstream factors have yet to be elucidated in the neotenic differentiation. A recent previousstudy in the damp-wood termite Hodotermopsis sjostedti, established a method inducing neotenic differentiation byartificially manipulating sex ratio of reproductives in experimental colonies. In this study, therefore, JH quantification andexpression analyses on the putative downstream genes were carried out during the neotenic differentiation. JH titer andthe downstream genes (Met, Kr-h1) were shown to be temporarily lowered, but increased just prior to the molt intoneotenics. In contrast, a transcription factor E93 that acts downstream of ecdysone was up-regulated at earlier stageof the neotenic differentiation, suggesting that the activation of E93 under low JH titer may lead the neotenicdifferentiation. Furthermore, it was predicted that the downstream factors of JH were regulated in the body part-specificmanner, since the body part-specific morphogenesis in the caste differentiation is induced by JH, which is a globalfactor carried throughout the body by circulatory systems. Comparisons of expression levels among body partsshowed that the downstream genes were highly expressed in abdomens, suggesting that the downstream responsesof JH lead developments of gonads and genital structures in the neotenic differentiation.