A general model for the evolution of mutualisms

TLDR

The evolution of mutualisms is a puzzle that our model connects to existing theories and empirical evidence. The study seeks to explain why selection favors cooperation over cheating by presenting a general model that identifies key factors and allows assessment of their relative importance. The model predicts that high benefit‑to‑cost ratio, high within‑species relatedness, and high between‑species fidelity drive mutualism evolution by moderating cooperator association, partner‑fidelity feedback, and partner choice, enabling assessment of their relative importance. The model shows that phenotypic feedbacks—partner‑fidelity feedback and partner choice—explain between‑species cooperation better than genetic correlations among species.

Abstract

The evolution of mutualisms presents a puzzle. Why does selection favour cooperation among species rather than cheaters that accept benefits but provide nothing in return? Here we present a general model that predicts three key factors will be important in mutualism evolution: (i) high benefit to cost ratio, (ii) high within-species relatedness and (iii) high between-species fidelity. These factors operate by moderating three types of feedback benefit from mutualism: cooperator association, partner-fidelity feedback and partner choice. In defining the relationship between these processes, our model also allows an assessment of their relative importance. Importantly, the model suggests that phenotypic feedbacks (partner-fidelity feedback, partner choice) are a more important explanation for between-species cooperation than the development of genetic correlations among species (cooperator association). We explain the relationship of our model to existing theories and discuss the empirical evidence for our predictions.