A winged élite in a subcortical beetle as a model for a prototermite

Abstract

TRUE sociality has evolved in only two insect orders—the Hymenoptera (ants, bees and wasps) and the Isoptera (termites). The hymenopterans seem to have achieved social organisation on at least 11 independent occasions¹; this seems to have been facilitated by their haplodiploid sex determination which predisposes them to evolution of a caste system based on altruism². Among the termites, fundamental similarities of social adaptation and organisation indicate a monophyletic origin; but in the absence of haplodiploidy, the conditions in which eusociality has arisen remain obscure. I report here a reproductive polymorphism in tiny feather-winged beetles (family Ptiliidae) living in dead wood, in which winged females are super-reproductive. The parallel with the winged reproductives of termite societies is striking and to my knowledge has not previously been observed in a non-social insect. The selection pressures that resulted in this convergent evolution may reflect those with which the prototermite had to contend during early socialising stages. This may be a better model for the prototermite than the currently favoured blattoid Cryptocercus¹. The model is, of course, entirely one of an analogy based on convergence; there is no suggestion that there is any phylogenetic link.