COS 242-3 - CANCELLED - The evolution of partner specificity in mutualism

Abstract: Mutualistic species vary in their level of partner specificity, which has important evolutionary, ecological, and management implications. Yet, the evolutionary and ecological mechanisms which underpin partner specificity are not fully understood. Most work on specialization focuses on the trade-off between generalism and specialism, where specialists receive more benefits from preferred partners at the expense of benefits from non-preferred partners, while generalists receive similar benefits from all partners. Because all mutualisms involve some degree of both cooperation and conflict between partners, we highlight that specialization to a mutualistic partner can be cooperative, increasing benefit to a focal species and a partner, or antagonistic, increasing resource extraction by a focal species from a partner.

We devise an evolutionary game theoretic model to assess the evolutionary dynamics of cooperative specialization, antagonistic specialization, and generalism. Our model shows that cooperative specialization leads to bistability: stable equilibria with a specialist host and its preferred partner excluding all others. We also show that under cooperative specialization with spatial effects, generalists can thrive at the boundaries between differing specialist patches. Under antagonistic specialization, generalism is evolutionarily stable.

We extend this game theoretic model to examine how variation in environment quality shapes the evolution of the genotypic match between mutualistic partners, and variation in mutualist quality. We find that variation in habitat quality across space promotes coexistence of specialist phenotypes, enhancing variation in mutualist quality. Ecological trade-offs between matching mutualistic partners and the local habitat had divergent implications for the evolution of partner specificity.

We provide predictions for how a cooperation-antagonism continuum, and variation in habitat quality may determine the patterns of partner specificity that develop within mutualistic relationships.