Group formation in a social wasp

Group formation is a fundamental step in the evolution of cooperation, yet there are few models of this process in social animals, and even fewer empirical tests. The prolonged nest initiation phase in temperate paper wasps provides a valuable opportunity to study group formation. Data were obtained for 180 groups of females collected from a large population of Polistes dominulus in two sites in south-western Spain. Foundresses on early nests were more closely related then females in winter aggregations or in stable groups (just before workers emerged). Most stable groups (£ 85 %) had one or more females that were unrelated (or distantly related) to the remaining members of the group. Mean wasp size did not markedly change during the different stages of the nesting cycle. Only 15 % of all foundresses had one or more clypeal marks. Wasps with marks were more common at the end of the nest foundation period than at early nests suggesting that these wasps may be adopting a “sit and waif strategy. Foundresses that hibernated in the same aggregation were more likely to start a nest together. Changes in group composition were likely to be caused by the disappearance of foundresses (death) and the frequent arrival of joiners to established groups. Within-group relatedness was not affected by the arrival of late joiners, but was negatively correlated with the date that nests were initiated. Only 16 % of all successfully marked wasps visited more than one nest. These wasps tended to move to nests with higher within-group relatedeness and less clypeal marks variability than their original group, but not necessarily a higher number of their own relatives. Dominance hierarchies were experimentally inferred for 53 nests. Rank was negatively correlated with the number of full-sisters foundresses an individual had in its group. Highly-ranked wasps (rank 1 and 2) were less likely to share a nest with their full-sisters than wasps of lower rank, but an individual’s rank was not affected by whether its full-sisters had a higher or lower position than it in the dominance hierarchy. Rank was also correlated with the size of clypeal marks, but only one foundress had a mark on 15 nests out of the 20 nests where wasp with marks were present (out of 53).