The presence of reproductively altruistic castes is one of the primary traits of the eusocial societies. Adaptation and regulation of the sterile caste, to a certain extent, drives the evolution of eusociality. Depending on adaptive functions of the first evolved sterile caste, eusocial societies can be categorized into the worker-first and soldier-first lineages, respectively. The former is marked by a worker caste as the first evolved altruistic caste, whose primary function is housekeeping, and the latter is highlighted by a sterile soldier caste as the first evolved altruistic caste, whose task is predominantly colony defense. The apparent functional differences between these two fundamentally important castes suggest worker-first and soldier-first eusociality are potentially driven by a suite of distinctively different factors. Current studies of eusocial evolution have been focused largely on the worker-first Hymenoptera, whereas understanding of soldier-first lineages including termites, eusocial aphids, gall-dwelling thrips, and snapping shrimp, is greatly lacking. In this review, we summarize the current state of knowledge on biology, morphology, adaptive functions, and caste regulation of the soldier caste. In addition, we discuss the biological, ecological and genetic factors that might contribute to the evolution of distinct caste systems within eusocial lineages.
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This research was supported by a start-up fund from the University of Kentucky, a grant from the Kentucky Commercialization Fund Program, Kentucky Science and Technology Corporation (Award Agreement No. KSTC-144-401-09-034), and the Research Support Grant Program sponsored by the University of Kentucky Office of the Vice President for Research. The granting agencies have no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Tian, Li and Zhou, Xuguo, "The Soldiers in Societies: Defense, Regulation, and Evolution" (2014). Entomology Faculty Publications. 70.