A general model for the evolution of mutualisms

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.

Altruism in insect societies and beyond: voluntary or enforced?

“…Inclusive fitness: the total fitness of an actor resulting from its own reproduction (direct fitness) and the effect it has on the reproduction of others, weighted by relatedness (indirect fitness) [4]. Mutualism: a cooperative interaction that increases the lifetime direct fitness of both the actor and one or more recipients -partners generally belong to different species [4,54]; as for altruism, mutualism can be either voluntary or enforced (i.e. it can occur with or without coercion).…”

“…Coercion and enforced cooperation are not restricted to insect societies but also occur in vertebrate [12,50] including human [51,52] societies and multispecies mutualisms [53][54][55] (Figure 1). In contrast to insect societies, however, in which coercion typically promotes inequality in a group composed of related individuals [5], in human society and in mutualisms, coercion often promotes fairness and reduces exploitation or cheating in groups with low or zero relatedness [51,54]. In other words, coercion is used to promote cooperation rather than altruism.…”

“…In other words, coercion is used to promote cooperation rather than altruism. Another difference is that, whereas coercion in insect societies usually has indirect inclusive-fitness benefits, in social vertebrates and mutualisms it usually provides direct benefits [53,54]. For example, in mutualisms, individuals can terminate interactions with uncooperative partners, thereby focusing interactions onto more cooperative partners [53,54,56].…”

“…Another difference is that, whereas coercion in insect societies usually has indirect inclusive-fitness benefits, in social vertebrates and mutualisms it usually provides direct benefits [53,54]. For example, in mutualisms, individuals can terminate interactions with uncooperative partners, thereby focusing interactions onto more cooperative partners [53,54,56]. Similarly, in social vertebrates, punishment can have direct benefits to the punishing individual, such as by inducing the victim to behave more cooperatively in the future [50].…”

Symbiont fidelity and the origin of species in fungus-growing ants

“…The long-term stability and success of mutualisms present a challenge for evolutionary theory, for how can such cooperative associations persist, much less proliferate, when selection favours selfishness and conflict 4,6,7 ?…”