Game of Thrones : Direct Fitness through Nest Foundation in the Primitively Eusocial Wasp Ropalidia Marginata

Abstract

Reproduction is the avenue for gaining direct fitness. But in certain species some individuals do not reproduce, instead gain indirect fitness by helping relatives to reproduce; the prime examples for this come from the worker caste of social insects like ants, bees and wasps. For explaining such a perplexing paradox, also known as altruism, W.D. Hamilton proposed that individuals can gain fitness in two ways: directly, by reproducing (direct fitness), and indirectly, by helping relatives to reproduce (indirect fitness). Indirect fitness has since been the main focus for explaining the evolution of workers while usually overlooking the fact that workers can also gain direct fitness. One of the avenues for gaining direct fitness by workers is nest foundation and we have studied this phenomenon in a primitively eusocial wasp Ropalidia marginata. We found that workers routinely leave their natal nests to initiate new nests either alone or with a few other wasps. Before leaving their natal nests, such workers prepare in several ways for nest foundation, like enhancing their nutrient reserves and forming outside nest aggregations to engage in dominance interactions. Next, we investigated the emergence of cooperation and division of labour in newly founded nests and how these affect the productivities of the new nests. We found that while two wasps are sufficient for the emergence of cooperation and reproductive division of labour (DOL), it takes three wasps for non-reproductive DOL to emerge; cooperation and reproductive DOL are not sufficient for increasing colony productivity which comes about only with the addition of non-reproductive DOL. Finally, we found that it is ageing and nutrition, and not work done towards gaining indirect fitness that affect workers’ potential of gaining future direct fitness by independent reproduction via nest foundation, in other words, current indirect fitness is not incompatible with future direct fitness.