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  • Comp. by: SUNDARAVARADARAJULU Stage: Proof Chapter No.: 5 Title Name: RubensteinAndAbbot Date:7/12/16 Time:12:49:21 Page Number: 124

    5 Sociality in Termites Judith Korb and Barbara Thorne

    Overview

    Termites are biologically unique because, across all known living creatures, termites have the most diverse array of distinct body forms encoded by a single genome. These different morphologies characterize separate castes within termite societies, including up to three types of reproductives of each sex, and depending upon the species, several castes of workers and soldiers. No microbe, plant, or animal – including other eusocial taxa – rival the breadth of polyphenism found within termite species. The exceptional behavioral and physiological specializations facilitated by varying internal and external morphologies of these diversified castes, and the resulting flexibility and adaptability afforded an integrated colony, comprise one of the fundamental drivers of termites’ ecological success and evolutionary radiation. Another key component of termite abundance and prosperity in many ecosystems is their exclusive niche among eusocial insects (as well as most of other animals): termites feed and often nest in or around dead plant material. Although a cellulose-based diet has its challenges, termites have evolved “clever” innovations to thrive as detritivores. Exploiting the vast and relatively uncrowded plant decomposer niche has contributed to termites’ success, and has rendered their activities critical to nutrient cycles and other essential dynamics of tropical forests, savannahs, and other ecosystems.

    I SOCIAL DIVERSITY

    5.1 How Common is Sociality in Termites?

    Termites are “eusocial cockroaches,” a monophyletic clade of diploid insects (Infra- order Isoptera) within the order Blattaria (Inward et al., 2007a; Lo et al., 2007; Engel et al., 2009; Krishna et al., 2013). All of the nearly 3,000 species of modern termites (Krishna et al., 2013) are eusocial, as they have sterile soldiers, a trait which is only secondarily lost in some Termitidae (Noirot & Pasteels, 1987). Termites have castes of

    We thank Dustin Rubenstein and Patrick Abbot for the invitation to write this review and for all their and other contributors’ efforts invested in this book. J. K. acknowledges NESCent and the German Funding Foundation for support. Both authors salute our colleagues, and fascinating termites, for exciting adventures, unexpected discoveries, and the delights of integrating field and laboratory work with comparative biology and theory.

    124

  • Comp. by: SUNDARAVARADARAJULU Stage: Proof Chapter No.: 5 Title Name: RubensteinAndAbbot Date:7/12/16 Time:12:49:21 Page Number: 125

    reproductives, workers, and soldiers, but differ conspicuously from eusocial Hymenop- tera in being hemimetabolous (i.e. gradual development of same body plan via molts through juvenile stages to adult) and in having morphologically versus allometrically distinct sterile soldiers. Because of hemimetabolous development, termites beyond the first instars are not helpless as are juvenile Hymenoptera larvae. Additionally, like some social vertebrates, but again in contrast to Hymenoptera, termites of both sexes are diploid and serve as helpers: female and male parents (i.e. queen and king) survive after initial mating, help rear the first brood, and continue to mate periodically.

    5.2 Forms of Sociality in Termites

    Levels of social organization and developmental flexibility differ distinctly across termite taxa, corresponding tightly to nest and foraging habits (so called “life types”) (Tables 5.1 and 5.2). Social organization ranges from simple colonies with small colony sizes in which each individual has a high developmental plasticity, to some of the largest and most complex societies among animals in which the caste fate of each member is determined in the egg. Modern termites fall into two fundamental groups, with just a few species showing intermediate characteristics: One Piece Life Type Termites (hereafter OPT; terminology from Abe, 1987; thought to reflect ancestral life history patterns (Noirot, 1985a; Abe, 1987; Noirot & Pasteels, 1987; Noirot & Border- eau, 1988; Grandcolas & D’Haese, 2004; but see also Watson & Sewell, 1981); and Separate Type Termites (hereafter ST; Abe, 1987). This distinction in life type is reflected mainly in the worker caste (reviewed in Roisin & Korb, 2011). Soldiers do not differ as dramatically between OPT and ST species; in most species soldiers have a defensive role within the colony, but they can also serve as scouts and be involved in foraging (Traniello & Leuthold, 2000). A termite soldier is always a final (terminal) instar that develops via two molts through a presoldier intermediate. Soldiers are sterile and hence can gain only indirect fitness.

    5.2.1 One Piece Life Type Termites (OPT)

    OPT species (also called “single site,” Noirot, 1970; “single-site nesters,” Shellman- Reeve, 1997; or “wood-dwellers,” Korb, 2007a) spend their entire lives nesting and feeding within the same single tree, log, stump, or piece of wood where their founding queen and king first initiated the colony. They are restricted to that one resource, and do not search for or exploit nearby pieces of wood (only rare cases of “house hunting” occur, Rupf & Roisin, 2008). These termites must cope with the nutritional, moisture, thermal, competitive, predator, pathogen and parasite circumstances within their nest wood, including inevitable changes over time. When their sole resource is depleted or otherwise inhospitable, the colony dies. Their only option for relocation is for develop- mentally agile individuals within the colony to differentiate into winged sexuals (alates) and disperse by flight to attempt to found their own colonies.

    125Sociality in Termites

  • Comp. by: SUNDARAVARADARAJULU Stage: Proof Chapter No.: 5 Title Name: RubensteinAndAbbot Date:7/12/16 Time:12:49:21 Page Number: 126

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