Ecological Drivers of Non-kin Cooperation in the Hymenoptera

Madeleine M Ostwald,Jennifer H Fewell,Brian R Haney

doi:10.3389/fevo.2022.768392

Madeleine M Ostwald, Jennifer H Fewell + Show 1 more

Open Access

https://doi.org/10.3389/fevo.2022.768392

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Abstract

Despite the prominence of kin selection as a framework for understanding the evolution of sociality, many animal groups are comprised of unrelated individuals. These non-kin systems provide valuable models that can illuminate drivers of social evolution beyond indirect fitness benefits. Within the Hymenoptera, whose highly related eusocial groups have long been cornerstones of kin selection theory, groups may form even when indirect fitness benefits for helpers are low or absent. These non-kin groups are widespread and abundant, yet have received relatively little attention. We review the diversity and organization of non-kin sociality across the Hymenoptera, particularly among the communal bees and polygynous ants and wasps. Further, we discuss common drivers of sociality across these groups, with a particular focus on ecological factors. Ecological contexts that favor non-kin sociality include those dominated by resource scarcity or competition, climatic stressors, predation and parasitism, and/or physiological constraints associated with reproduction and resource exploitation. Finally, we situate Hymenopteran non-kin sociality within a broader biological context by extending insights from these systems across diverse taxa, especially the social vertebrates. Non-kin social groups thus provide unique demonstrations of the importance of ecological factors in mediating the evolutionary transition from solitary to group living.

Highlights

Social animals represent some of the most ubiquitous and ecologically dominant organisms globally (Hölldobler and Wilson, 1990; Krause and Ruxton, 2002; Ward and Webster, 2016)
Departures from a kin-centric framework for understanding insect social evolution may enable valuable connections to other animal groups, contributing to a broader body of evolutionary theory. These systems may be neglected because interactions among non-kin rarely constitute altruism—that is, behavior that reduces the fitness of the actor and increases the fitness of the group—which has been a major focus of social evolutionary research in the eusocial Hymenoptera (Hamilton, 1972; Simon, 1990; Foster et al, 2006; Kennedy et al, 2018)
The presence of non-relatives in social groups has been inferred from observations of nest-joining behavior, often by individuals from distant nests, or of cooperative nest founding by presumed unrelated foundresses

Summary

INTRODUCTION

Social animals represent some of the most ubiquitous and ecologically dominant organisms globally (Hölldobler and Wilson, 1990; Krause and Ruxton, 2002; Ward and Webster, 2016). The presence of non-relatives in social groups has been inferred from observations of nest-joining behavior, often by individuals from distant nests (in bees and wasps), or of cooperative nest founding by presumed unrelated foundresses (in wasps and ants) Though these observations cannot confirm the degree of relatedness between joiners and their nestmates, they provide suggestions of potential flexibility in tolerance toward unrelated conspecifics. The social organization of some non-kin bee groups is more aptly described by the umbrella term “parasocial,” which includes all associations of same-generation adults, which may be cooperative or non-cooperative, and which may exhibit high or low reproductive skew (Michener, 1974) This is the case for many bees of the family Apidae, which includes both solitary and highly social species.

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