The Ground Plan

Nature has set a very high bar for the attainment of euso-ciality, and only extraordinary environmental challenges and extraordinary circumstances in prior history can allow an organism to scale it (Holldobbler and Wilson, 2005). In the termite ancestor, a nitrogen-deficient, physically difficult food source was undoubtedly the relevant environmental challenge, and costly brood care was an essential precedent. Nonetheless, the evolution of termite eusociality cannot be divorced from an entire suite of interrelated and influential morphological, behavioral, developmental, and life history characteristics. These include monogamy, altricial offspring, adult longevity, extended developmental periods, multiple relationships with microbial symbionts, proctodeal trophallaxis and other food-sharing behaviors, reproduction and development that closely track nutritional status, and semelpar-ity with age differentials within the brood (Nalepa, 1984, 1994). So many conditions were interrelated, aligned, and influential in the transition that any attempt to reduce an explanation to a few basic elements is an oversimplification. It is important to note, however, that in integrated character sets such as these, selection on just one character can lead to changes in associated characters, and these changes can occur with a minimum of genetic change. It is in this manner that paedomorphic evolution often proceeds, with small tweaks in regulatory genes that result in maximum impact on an evolutionary trajectory (Gould, 1977; Futuyma, 1986; Stanley, 1998). It is also notable that all ground plan elements are found among extant cockroaches, and that the core process, as in other social insects (Hunt and Nalepa, 1994; Hunt and Amdam, 2005), is a shift in life history characters mediated by a nutrient-dependent switch.

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