Effects of juvenile hormone III on morphogenetic changes during a molt from each nymphal instar in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Abstract

Termite castes are defined by their specific characteristics. It is said that juvenile hormone (JH) plays an important role in caste differentiation and JH has been shown to highly influence imaginal-organ development, as well as soldier-specific morphogenesis in some species. To provide additional comparative data for interpreting the effects of JH on the development of alate and soldier characteristics, we performed morphological investigations on newly molted individuals from different nymphal instars of Reticulitermes speratus induced by various concentrations of JH III. As a result, each organ (especially wing (-bud) and mandible) development was shown to be strongly affected by JH III in each nymphal instar. Moreover, depending on the JH III concentration, there was a trade-off-like relationship between wing formation (alate character) and mandibular elongation (soldier character) only in molted individuals from final instar nymphs. Our results suggest that the endogenous JH titer or the threshold titer for caste-specific morphogenesis changes via nymphal development in R. speratus. This study shows that highly developmental plasticity is retained in the derived species of termites, and that it must be a driving force of caste evolution.

What Kills the Hindgut Flagellates of Lower Termites during the Host Molting Cycle?

“…The timing, amplitude and duration of ecdysone pulses are key in initiating and controlling such developmental transitions by activating signaling cascades in target tissues [ 116 ]. Most work on the endocrinology of caste determination in termites to date has focused on the role of juvenile hormone (JH), e.g., [ 111 , 117 , 118 , 119 , 120 , 121 ], but ecdysone and JH act in concert as key endocrine timers in precisely controlling the onset of developmental transitions and in harmonizing gene expression profiles [ 116 , 122 , 123 ]. The recognition of cross-talk between these two classes of hormones may be key in determining the endocrine basis of termite caste determination [ 115 , 124 , 125 ] particularly as these hormones are thought to be overlooked players in the epigenetic control of gene expression [ 126 ].…”

Reproductive Soldier Development Is Controlled by Direct Physical Interactions with Reproductive and Soldier Termites

“…Generally, in insects, there is a trade-off between weapon size and reproductive organ size [ 18 , 19 , 20 ]. Furthermore, such trade-offs might be mediated by JH in stalk-eyed flies [ 19 ] and termites [ 21 , 22 ]. It is interesting to note that the head phenotypes of the reproductive soldiers, with their small mandibles, were highly similar to those of molted soldiers after RNAi-mediated knockdown of the JH receptor gene [ 12 ].…”

Soldier Caste-Specific Protein 1 Is Involved in Soldier Differentiation in Termite Reticulitermes aculabialis

“…In addition, during soldier differentiation, JH may participate in not only the soldier molting process but also the morphogenesis of soldier special weapons, especially the mandibles [ 15 , 16 , 17 , 18 ]. Thus, as the most critical endocrine regulator to control soldier differentiation, the JH signaling pathway have been the focus for exploring the phenotypic plasticity mechanism [ 3 , 19 ].…”