Evolutionary Biology & Ecology, University of Freiburg, Hauptstrasse 1, D-79104 Freiburg, Germany.
Institute of Evolutionary Biology, CSIC-Universitat Pompeu Fabra, Passeig Marítim 37, 08003 Barcelona, Spain.
Curr Opin Insect Sci. 2017 Aug;22:109-116. doi: 10.1016/j.cois.2017.06.002. Epub 2017 Jun 15.
Termites are social Dictyoptera that evolved eusociality independently from social Hymenoptera. They are characterized by unique developmental plasticity that is the basis of caste differentiation and social organization. As developmental plasticity is a result of endocrine regulation, in order to understand the evolution of termite sociality it is helpful to compare the endocrine underpinning of development between termites and cockroaches. Nijhout and Wheeler (1982) proposed that varying JH titers determine caste differentiation in termites. Based on current results, we extend this model by adding the importance of social interactions. High JH titers in the presence of soldiers lead to regressive development (decrease in body size, apparent regression in development), while an absence of soldiers induces (pre-)soldier differentiation. On the opposite side, low JH titers in colonies headed by reproductives result in progressive molts toward adults, while an absence of reproductives induces development of replacement reproductives. In cockroaches, transcription factors involved in JH signaling, including the adult specifier E93 (the co-called MEKRE93 pathway) regulate the morphogenetic transition between the nymph and the adult. In termites, we speculate that castes might be determined by social effects playing a modulatory action of JH in the MEKRE93 pathway.
白蚁是社会性的直翅目昆虫，它们独立于社会性膜翅目昆虫进化出了真社会性。它们具有独特的发育可塑性，这是级型分化和社会组织的基础。由于发育可塑性是内分泌调节的结果，为了了解白蚁社会性的进化，比较白蚁和蟑螂之间发育的内分泌基础是有帮助的。Nijhout 和 Wheeler（1982）提出，变化的 JH 浓度决定了白蚁的级型分化。基于目前的结果，我们通过添加社会相互作用的重要性来扩展这个模型。在有兵蚁存在的情况下，高 JH 浓度会导致退化发育（体型减小，发育明显退化），而没有兵蚁则会诱导（预）兵蚁分化。相反，在由生殖蚁领导的群体中，低 JH 浓度会导致向成虫的渐进蜕皮，而没有生殖蚁则会诱导替代生殖蚁的发育。在蟑螂中，参与 JH 信号转导的转录因子，包括成虫决定因子 E93（所谓的 MEKRE93 途径），调节着若虫和成虫之间的形态发生过渡。在白蚁中，我们推测，级型可能是由社会效应决定的，这些社会效应在 MEKRE93 途径中对 JH 起着调节作用。
