INDIVIDUAL AND COLONY LIFE HISTORY OF PTEROTERMES OCCIDENTIS AND ITS RELATION TO THEORIES OF TERMITE EVOLUTION (EUSOCIALITY, WORKERS, FITNESS).

Abstract

Pterotermes is a very primitive genus of the lower termite family Kalotermitidae. Entire colonies were collected from standing dead Cercidium (palo verde) near Tucson, AZ. Most were maintained and recensused. Some were partitioned into groups by caste and instar, and the groups followed to determine developmental fates. Sorted material was preserved for morphometrics. Alate pairs were sealed in chambers in two sizes of palo verde and colonies allowed to grow. New colonies grow for several years, producing only "larvae" which develop into large workers, with occasional maturation to soldier form. Then most fifth or sixth instar larvae of upcoming cohorts undergo three nymphal instars before maturing to alates which leave to found new colonies. Workers do not seem to mature to alates, but may become soldiers or neotenic reproductives. Colonies are headed by a single royal pair, usually the founders, especially the founding queen (84%). Workers can be recruited by biting the wing bud region of larvae or nymphs. Bitten termites develop toward worker form. Workers may be biting siblings to recruit helpers, perhaps improving their own indirect fitness. In the two sizes of wood, no colony consumed more than a fraction of the wood volume, yet colonies in small branches restricted egg crop, hence colony, growth. In the field, branch size was a good predictor of colony size (r-squared 0.80). A theory is proposed based on spreading reproductive output over the expected lifespan of the royal pair. The data are interpreted to support a view of colonies as largely under royal pair control. Pterotermes seems to exhibit the worker-nymph developmental dimorphism proposed by Watson and Sewell (1981) to be an ancestral feature of termite biology. A scheme of origin is proposed, in which the parents suppressed facultative neotenic maturation, then all sexual maturation of earliest offspring. Workers were the result of arrested maturation (see also Myles, 1983). It is argued that once eusociality evolves, close genetic relatedness of colony members is not required for maintenance of the system, as long as some minimal degree of family structure remains.