In the Isoptera, day-to-day colony labor is the responsibility of juveniles—termites whose development has been truncated, either temporarily or permanently, relative to reproductives. Even terminal nonsexual stages (i.e., soldiers, and workers in some species) are considered immature, because they retain their prothoracic glands, which degenerate in all sexual forms. The only imagoes in the termitary are the king and queen (Noirot, 1985; Noirot and Pasteels, 1987; Noirot and Bordereau, 1989). The degree, permanence, timing, and reversal of developmental arrest, together with the organs subject to these changes, determine which developmental pathway is taken during the ontogeny of particular groups (Noirot and Pasteels, 1987; Roisin, 1990, 2000). This developmental flexibility is mediated by a combination of progressive, stationary, and reversionary molts, and is distinctive. Dedifferentiation of brachypterous nymphs in termites is the only known instance of a natural reversal of metamorphosis in insects (Nijhout and Wheeler,
1982). The extraordinary complexity and sophistication characteristic of termite development is nonetheless rooted in mechanisms of postembryonic development observed in non-eusocial insects (Bordereau, 1985). The developmental characteristics of cockroach ancestors, then, were the phylogenetic foundation on which termite polyphenisms were built.
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