Philopatric reproduction, a prime mover in the evolution of termite sociality?

Abstract

Philopatric reproduction commonly occurs even in the most basic isopteran lineages and is almost certainly a primitive potentiality of these insects. Several authors hypothesized that opportunities for philopatric reproduction may have been a prime mover for the three most remarkable events in the evolution of termite sociality: the origin of helping behaviour, the origin of soldiers, and the origin of a permanently apterous worker caste. A critical assessment of these hypotheses and a review of relevant evidence are presented here. I first discuss the hypothesis that termite helpers derive from individuals choosing to postpone dispersal because of nest inheritance prospects. Such individuals would have developed helping as a strategy yielding indirect reproductive benefits while they wait for reproductive opportunities. However, it appears that prospects of philopatric reproduction need not be invoked to explain the origin of helping behaviour, which can be justified more parsimoniously by a favourable intrinsic benefit/cost ratio. Second, the hypothesis that soldiers originated through selection for fighting abilities among neotenic reproductives is found to face important difficulties, the major one being how to explain the absence of fighting devices in almost all present-day neotenics. Finally, the hypothesized link between apterism and chances of philopatric reproduction, which might have favoured the onset of the worker caste, is poorly supported by empirical evidence. It appears thus that philopatric reproduction, notwithstanding its importance in the biology of many extant termite species, is unlikely to have been a prime mover in the evolution of helping and of altruistic castes in termites.