Histology of the hormone-producing glands in the damp-wood termite Hodotermopsis sjostedti (Isoptera, Termopsidae): A focus on soldier differentiation

Abstract

Caste differentiation in termites depends on complex hormonal changes during postembryonic development. Juvenile hormone (JH) is a central player in this process. The present study examined histological changes in the main hormone-producing endocrine glands, the corpora allata and molt glands, in the Japanese dampwood termite Hodotermopsis sjostedti. We focused on the soldier caste differentiation pathway, which can be induced artificially using an analogue of JH. The corpora allata exhibited volumetric changes during soldier induction, reflecting variations in the quantity of cytoplasm. Corpora allata from alates and neotenics clearly showed differentiation accompanied by cell proliferation, preparing for the high-level JH production necessary for reproduction. However, the volume increase of corpora allata was not always correlated to high JH titers. In contrast, molt glands degenerated in the reproductive castes. The JH analogue induced hypertrophy of the molt glands, along with the formation of lacunae, possibly related to ecdysteroid production. The JH analogue effect, inducing soldier differentiation, was suggested to require both mimic of high JH titers and stimulation of the molt glands.

Ecdysone signaling regulates soldier‐specific cuticular pigmentation in the termite Zootermopsis nevadensis

“…The present study clearly showed that caste‐specific morphogenesis (especially soldier cuticular pigmentation) requires 20E signaling gene expression changes as well as JH activity. In the damp‐wood termite Hodotermopsis sjostedti , hypertrophy of the prothoracic gland was observed in presoldiers . We suggest that, as well as EcR activity, 20E synthesis level changes may also be involved in the soldier‐specific cuticular tanning.…”

Soldier Morphogenesis in the Damp‐Wood Termite Is Regulated by the Insulin Signaling Pathway

“…In termite caste differentiation, it has long been known that JH plays a critical role (Nijhout and Wheeler, ), and in H. sjostedti , JHA application induces growth of the corpora allata around Day 7 (Cornette et al, ). Our results show that IIS signaling was increased by JHA application, suggesting that the IIS pathway may also act downstream of JH.…”

“…3F). A histological study has shown that the prothoracic glands undergo growth at Day 7, prior to the presoldier molt (Cornette et al, 2008a). Recent evidence for a link between the IIS pathway and ecdysone action in determining body size (Caldwell et al, 2005;Colombani et al, 2005;Mirth et al, 2005) suggests that IIS may accelerate soldier differentiation by triggering prothoracic gland activity.…”

Expressions of juvenile hormone biosynthetic genes during presoldier differentiation in the incipient colony of Zootermopsis nevadensis (Isoptera: Archotermopsidae)

“…Keywords Social insects · Caste differentiation · Gene expression · CYP15 · JHAMT * Kiyoto Maekawa kmaekawa@sci.u-toyama.ac.jp 1 Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan changes were identified (e.g., Cornette et al 2008bCornette et al , 2013Koshikawa et al 2005;Masuoka et al 2013;Toga et al 2012Toga et al , 2013Watanabe and Maekawa 2012). However, it is still unknown when the genes involved in JH biosynthesis are activated and/or the JH titer increases during soldier differentiation under natural conditions.…”