Evolution of Eusociality: Lessons from Social Organization in Ropalidia Marginata (Lep.) (Hymenoptera:Vespidae)

In the primitively eusocial wasp Ropalidia marginata which lacks morphological caste differentiation, all adult females on a nest can be assigned to one of the three behavioural castes namely, Sitters, Fighters and Foragers (1). Here we explore the manner in which social organization and division of labour are achieved through such a behavioural caste differentiation. To do this, we examine the behavioural, morphological and anatomical correlates of behavioural castes in 12 post-emergence colonies of R. marginata from Bangalore and Mysore, India. Our sampling methodology and the variables used in the study are described elsewhere (1,2). Analysis of time activity budgets of wasps as described before (1) showed the presence of three behavioural castes namely Sitters, Fighters and Foragers in all colonies. Logistic regression analysis revealed that the risky task of foraging for food is performed largely by Foragers. Having very poorly developed ovaries, Foragers have the least chance of becoming queens in the future. On the other hand intra-nidal tasks such as feeding larvae and nest building are shared by Sitters and Fighters. Fighters also showed dominance signficantly more often than either Sitters or Foragers. Both Sitters and Fighters have equally well developed ovaries and can be treated as hopeful queens. No morphological differences were seen between the three behavioural castes. A complex network of dominancesubordinate relationships rather than a simple linear hierarchy was evident in most colonies. The queens were not necessarily the most dominant animals in their colonies; in fact the queens did not show any dominance behaviour in three colonies. The frequency of dominance behaviour was correlated with the frequency of such behaviours as Feed larva, Extend walls of cells, and Build new cells, suggesting that individuals showing dominance behaviour also perform several intra-nidal tasks