The primary dilemma in evolutionarily stable mutualisms is that natural selection for cheating could overwhelm selection for cooperation. Cheating need not entail parasitism; selection favours cheating as a quantitative trait whenever less‐cooperative partners are more fit than more‐cooperative partners. Mutualisms might be stabilised by mechanisms that direct benefits to more‐cooperative individuals, which counter selection f...

Host sanctions that reduce the relative fitness of uncooperative symbionts provide a mechanism that can limit cheating and thus stabilise mutualisms over evolutionary timescales. Sanctions have been demonstrated empirically in several mutualisms. However, if multiple individual symbionts interact with each host, the precision with which individual cheating symbionts are targeted by host sanctions is critical to their short‐ an...

Intraspecific genetic variation can affect community structure and ecosystem processes (Bolnick et al . 2011). It can also influence phenotypic expression by genotypes within other species to produce genotype‐by‐genotype ( G × G ) interaction (Falconer & Mackay 1996). Evolution of one species drives correlated evolution of others when it causes G × G for fitness (Thompson 2005). However, the mechanisms by which species interac...