Abstract
Stable social groups usually consist of families. However, recent studies have revealed higher level social structure, with interactions between family groups across different levels of social organization in multiple species. The explanations for why this apparently paradoxical behaviour arises appear to be varied and remain untested. Here, we use automated radio-tagging data from over 1000 wasps from 93 nests and social network analyses of over 30 000 nest visitation records to describe and explain interactions across levels of social organization in the eusocial paper wasp Polistes canadensis. We detected three levels of social organization (nest, aggregation and community) which exchange ‘drifter’ individuals within and between levels. The highest level (community) may be influenced by the patchiness of high-quality nesting habitats in which these insects exist. Networks of drifter movements were explained by the distance between nests, the group size of donor nests and the worker-to-brood ratios on donor and recipient nests. These findings provide some explanation for the multi-level social interactions, which may otherwise seem paradoxical. Fitness benefits across multiple levels of social organization should be considered when trying to understand animal societies.
Highlights
Eusociality is a widespread phenomenon in the animal kingdom and is considered as one of the major evolutionary transitions of life [1]
Determining the extent, nature and biological importance of nest drifting in social insects has been an outstanding question since Hamilton first described the behaviour in tropical Polistes in his 1964 treatise on kin selection theory
Using over 30 000 records generated by an automated real-time monitoring system of over 1000 individually tagged paper wasps across 93 nests, we provide, to our knowledge, the most comprehensive analysis to date of inter-nest drifting in a social insect
Summary
Eusociality is a widespread phenomenon in the animal kingdom and is considered as one of the major evolutionary transitions of life [1]. The paradox of inter-nest drifting by workers—whereby workers spend time in neighbouring non-natal nests—was highlighted by W.D. Hamilton as an anomaly to his theory on the genetical evolution of social behaviour [12]; he describes the ‘transference of workers ... A previous study on this species found that greater than 50% of workers move between nests on which they appear to perform helping behaviour [9]; this finding was remarkable, this previous study was based on a small sample size (157 tracked wasps), did not take account of the inter-dependency of the data and was purely correlational, lacking any manipulation of the conditions that may shape patterns of drifting. Outstanding questions include whether these high-level social interactions are a general phenomenon that persists over time, whether drifting extends beyond the immediate vicinity of family groups and whether the observed inter-nest interactions are driven by adaptive traits. We experimentally manipulated helping pay-offs of specific nests to further identify the factors driving individuals’ decisions and investigate the possible adaptive significance of spatially struc- 2 tured, multi-level interactions
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