Eusocial insects have highly sophisticated societies, showing a conspicuous division of labor associated with different phenotypes. These castes show specific morphologies adapted to discrete tasks. Termite castes are divided into reproductives, workers, and soldiers. Individuals with soldier-like heads as well as developed gonads have been recorded in several primitive families, and are called reproductive soldiers. In some termite species, however, a trade-off-like developmental relationship has been shown between soldier and imaginal characteristics. Thus, while the mechanism that regulates the development of both characteristics in the same individual is interesting, the details are still unclear. We focused on juvenile hormone (JH), which is involved not only in termite caste differentiation, but also in the gonad development of many insects, and we aimed to clarify the effects of JH on the differentiation of reproductive soldiers in Zootermopsis nevadensis. We succeeded in the induction of individuals with reproductive soldier-like gross morphologies by JH analog (JHA) application to several developmental stages. We also observed that gonad development was significantly promoted by JHA application after molts in the induced reproductive soldier-like individuals, but not in natural soldiers. Finally, we confirmed that the gene expression level of vitellogenin was extremely high in the induced reproductive soldier-like individuals following JHA treatment after the molt. These results suggested that soldiers do not have regulatory mechanisms for gonad development involving JH, and the regulation of reproductive soldiers development is different from that of soldiers. Reproductive soldiers may have evolved independently from the soldier caste rather than from an intermediate stage of soldier evolution.
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Vol. 31 • No. 9