Pathways to social evolution: reciprocity, relatedness, and synergy

TL;DR

This paper develops a unified framework to analyze how reciprocity, relatedness, and synergy interact in social evolution, revealing complex effects overlooked by previous models and emphasizing their importance for understanding social behavior.

Contribution

It introduces models that integrate behavioral responses, relatedness, and synergy, showing their interactions influence social evolution in ways not captured by simpler indices.

Findings

Interactions among reciprocity, relatedness, and synergy are complex and significant.

Neglecting these interactions leads to incomplete understanding of social evolution.

Proximate mechanisms are evolutionarily stable when they balance responsiveness with ecological costs.

Abstract

Many organisms live in populations structured by space and by class, exhibit plastic responses to their social partners, and are subject to non-additive ecological and fitness effects. Social evolution theory has long recognized that all of these factors can lead to different selection pressures but has only recently attempted to synthesize how these factors interact. Using models for both discrete and continuous phenotypes, we show that analyzing these factors in a consistent framework reveals that they interact with one another in ways previously overlooked. Specifically, behavioral responses (reciprocity), genetic relatedness, and synergy interact in non-trivial ways that cannot be easily captured by simple summary indices of assortment. We demonstrate the importance of these interactions by showing how they have been neglected in previous synthetic models of social behavior both within and between species. These interactions also affect the level of behavioral responses that can evolve in the long run; proximate biological mechanisms are evolutionarily stable when they generate enough responsiveness relative to the level of responsiveness that exactly balances the ecological costs and benefits. Given the richness of social behavior across taxa, these interactions should be a boon for empirical research as they are likely crucial for describing the complex relationship linking ecology, demography, and social behavior.