Pre-imaginal biasing of caste in a primitively eusocial insect

Abstract

Primitively eusocial insects often lack morphological caste differentiation, leading to considerable flexibility in the social and reproductive roles that the adult insects may adopt. Although this flexibility and its consequences for social organization have received much attention there has been relatively little effort to detect any pre-imaginal effects leading to a bias in the potential caste of eclosing females. Experiments reported here show that only about 50 % of eclosing females of the tropical social wasp Ropalidia marginata build nests and lay eggs, in spite of being isolated from all conspecifics and being provided ad libitum food since eclosion. The number of empty cells in the parent nest, which we believe to be an indication of the queen’s declining influence, and a wasp’s own rate of feeding during adult life predict the probability of egg laying by eclosing females. These results call for an examination of the possibility that all females in primitively eusocial insect societies are not potentially capable of becoming egg layers and that reigning queens and possibly other adults exert an influence on the production of new queens.

A skew model for the evolution of sociality via manipulation: why it is better to be feared than loved

“…For example, in aculeate Hymenoptera the size of pollen balls constructed by the mother or the amount of food fed directly to the larvae determines o¡spring size and sometimes caste (e.g. Plowright & Jay 1968;Packer & Knerer 1985;Gadagkar et al 1988Gadagkar et al , 1990Frank & Crespi 1989; O'Donnell 1998; see also Field & Foster 1999). Moreover, among species of halictine bees, there is a close positive association between the extent to which subordinate workers are smaller than their mother, worker subfertility and female bias of the ¢rst brood (indicative of less dispersal by ¢rst-brood females or less queen supersedure) (Ordway 1965;Plateaux-Quenu 1967;Breed 1975Breed , 1976.…”

Queen succession in the primitively eusocial tropical waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

“…However, previous work has demonstrated that Sitters and Fighters have significantly better-developed ovaries compared to the Foragers and that there are no significant body size differences between the behavioral groups (Chandrashekara and Gadagkar,199la). Nor is body size a good predictor of the ability of isolated laboratory females to develop their ovaries and lay eggs (Gadagkar et al, 1988). …”

Evolution of social behaviour in the primitively eusocial waspRopalidia marginata: do we need to look beyond kin selection?

“…We suspect that it is a combination of physiological and ecological factors. We have evidence that female wasps in R. marginata have extremely variable reproductive potential [14] and at least half of them fail to build nests and lay eggs in spite of having all the resources to do so [15]. However, we do not fully understand the mechanism by which such variation in reproductive potential is produced.…”

“…However, we do not fully understand the mechanism by which such variation in reproductive potential is produced. Among the ideas proposed, parental manipulation is a likely candidate [15][16][17][18]. We have evidence that the significantly lower productivity of forced single foundresses may also arise owing to their inability to forage and feed a large quantity of brood and yet survive as well as voluntary single foundresses.…”