Dominance based reproductive queue in the primitively eusocial wasp, Ropalidia cyathiformis

摘要

Ropalidia cyathiformis is a primitively eusocial tropical paper wasp usually with a single dominant queen per colony. When the queen is removed, one and only one individual increases her aggression and becomes the new queen of the colony, unchallenged by any other worker. We refer to such a successor as a potential queen (PQ) until she lays her first egg. By removing the queen and successive PQs, we show that there is not just one successor but a strict reproductive hierarchy of up to 3 PQs, who succeed the queen one after the other. Of many variables tested, we found that only the frequency of dominance behaviour is a significant predictor of whether or not an individual is part of the reproductive hierarchy and also of her position in the hierarchy. Dominance behaviour, however, does not perfectly predict the position of an individual in the reproductive hierarchy because we show that an average of three more dominant individuals, are bypassed when an individual becomes the next queen or PQ. This is in contrast to the reproductive hierarchy in the conspecific Ropalidia marginata, where age rather than dominance behaviour is a predictor (though imperfect once again) of an individual's position in the queue. Taken together, our results suggest that (a) these two sister species have evolved two rather different mechanisms of reproductive caste differentiation, (b) that neither of them strictly conform either to the so-called "temperate" or "tropical" patterns of queen succession seen in most other species studied so far.