A Route to Direct Fitness: Natural and Experimentally Induced Queen Succession in the Tropical Primitively Eusocial Wasp Ropalidia marginata

Insect societies are hallmarks of cooperation because one or a few queens monopolize reproduction and several non-reproductive workers cooperatively raise brood. However, the loss of the queen exposes a colony to potential reproductive conflict, which is resolved only after a new queen takes over. We studied queen succession in natural and experimental colonies of the primitively eusocial wasp Ropalidia marginata to understand the proximate behavioral strategies involved in the resolution of this conflict . Previous work has shown that in this species, experimental queen removal always results in only one worker becoming hyper-aggressive and taking over the colony as its next queen, without ever being challenged. Here we show that even during natural queen turnover, one and only one worker becomes hyper-aggressive and takes over as the next queen, without being challenged. During natural queen turn-over, aggression of the successor may sometimes begin before the loss of the old queen and may sometimes decline more rapidly, unlike in the case of experimental queen removal. The successor begins to lay eggs sooner after a natural queen turn-over as compared to experimental queen removal. This is expected because workers might detect the gradual decline of the queen preceding her disappearance. Because queen succession is expected to be more prevalent in tropical perennial species, we expect natural selection to have favored such an orderly queen succession so that a route to direct fitness is available without significant reduction in cooperation.