Ontogenetic development and evolution of the worker caste in termites

Abstract

Summary. The hemimetabolous termites have a very different caste system from social Hymenoptera in which only true imagoes participate in all social tasks. In termites, the imagoes are restricted to reproduction. The termite solidiers have no equivalent in other social insects. They are unique both in their post-embryonic development and their exclusively defensive function. At maturity they keep their molting gland and therefore should be considered as stabilized, differentiated immatures. They appeared monophyletically, early in the evolution of termites. The definition of the worker caste and the current theories explaining its evolution are reexamined after a critical reappraisal of data on post-embryonic development. On the basis of ontogenic, morphologic and functional criteria, we define termite workers as individuals diverging early and irreversibly from the imaginal development, with a morphology typical of their caste but largely of larval appearance, and taking part in most of the social tasks. Such a truly eusocial worker caste is observed in all advanced phyla: Termitidae, Hodotermitidae, and Schedorhinotermes (Rhinotermitidae), but apparently also in one morphologically primitive termite, Mastotermes darwiniensis. This distribution can only be explained by postulating a polyphyletic origin of the worker caste in termites. In all other primitive termites, most of the work is done by temporary helpers (late larvae and nymphs). In these societies, pseudergates are redefined as individuals separating late from the imaginal line, functioning as workers, but not constituting the main working force in the natural society. The particularity of the caste system in termites results from two fundamental peculiarities of their post-embryonic development:-A certain dissociation of molt, growth, and differentiation.-A relative independence in the ontogeny of their different organs.

Emergent Specialization in Biologically Inspired Collective Behavior Systems

“…Specialization is often closely associated with, and sometimes synonymous with, heterogeneity in collective behavior systems (Balch, 1998), (Potter et al, 2001). Heterogeneity can be hardwired or plastic, and may assume either behavioral (Bryant & Miikkulainen, 2003), (Whiteson et al, 2003), (Noirot & Pasteels, 1987) or morphological (Schultz & Bugajska, 2000), (Zhang et al, 2003), (O'Riain, Jarvis, Alexander, Buffenstein, & Peeters, 2000) forms. Plastic heterogeneity is when a group adapts its degree of heterogeneity as a function of environment and task constraints, where as, hardwired heterogeneity is when the degree of heterogeneity in the group remains static (Li et al, 2002).…”

“…Over the course of evolutionary time, specialization in biological communities has assumed both morphological (Wenseleers, Ratnieks, & Billen, 2003) and behavioral forms (Bonabeau, Theraulaz, & 3 Deneubourg, 1996). For example, the morphologically specialized castes that have emerged in certain termite colonies (Noirot & Pasteels, 1987), and honey bees that dynamically adapt their foraging behavior for pollen, nectar, and water as a function of individual preference and colony demand (Calderone & Page, 1988). The consequence of such specializations is that labor is efficiently divided between specialized castes 2 and individuals for the benefit of accomplishing group tasks.…”

“…Many artificial collective behavior systems have used design principles which draw their inspiration from examples of specialization in nature. Such examples include complex ecological communities such as social insect colonies (Noirot & Pasteels, 1987), (Wenseleers et al, 2003), (Seligmann, 1999), (Calderone & Page, 1988), (Bonabeau et al, 1996), (Bonabeau, Sobkowski, Theraulaz, & Deneubourg, 1997), biological neural networks (Baev, 1997), multi-cellular organisms (Hawthorne, 2001), economies of a nation, companies, corporations and other business organizations (Resnick, 1997), (Abdel-Rahman, 2001), (Ng & Yang, 1997). Such biologically inspired design principles are especially prevalent in multi-robot (Potter, Meeden, & Schultz, 2001) swarm intelligence (Bonabeau, Dorigo, & Theraulaz, 1998) and artificial life systems (Nishimura & Takashi, 1997) where it is highly desirable to replicate the success of biological collective behavior systems.…”

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

“…Based on caste differentiation data in many species, Noirot and Pasteels (1987) proposed two fundamental traits of termite development responsible for their sociality: 1) certain dissociation of molt, growth, and differentiation, 2) relative independence in the ontogeny of the different organs. Because JH is the central factor for caste differentiation in termites, it is very important to know the effects of JH on the different organ development of each individual to understand the proximate mechanisms of caste differentiation.…”

Caste polymorphism of apterous line of the Neotropical termite Nasutitermes corniger (Motschulsky) (Isoptera, Termitidae)

“…Termite societies are structured with individuals that can be grouped into castes and stages of development. The system of castes can vary according with to family, genus and species of termites (Noirot & Pasteels 1987;Roisin 2000). In Termitidae, bifurcation occurs after the first stage of development.…”