Gene flow and metacommunity arrangement affects coevolutionary dynamics at the mutualism-antagonism interface.

Interspecific interactions are affected by community context and, as a consequence, show spatial variation in magnitude and sign. The selective forces imposed by interactions at the mutualism-antagonism interface are a consequence of the traits involved and their matching between species. If mutualistic and antagonistic communities are linked by gene flow, coevolution between a pair of interacting species is influenced by how selection varies in space. Here we investigate the effects of metacommunity arrangement, i.e. patterns of connection between communities and the number of communities, on the coevolutionary dynamics between two species for which the sign and magnitude of the interaction varies across the landscape. We quantify coevolutionary outcome as an index that can be decomposed into the contribution of intraspecific genetic diversity and interspecific interaction. We show that polymorphisms and mismatches are an expected outcome, which is influenced by spatial structure, interaction strength and the degree of gene flow. The index describes how variation is distributed within and between species, and provides information on the directionality of the mismatches and polymorphisms. Finally, we argue that depending on metacommunity arrangement, some communities have disproportionate roles in maintaining genetic diversity, with implications for the coevolution of interacting species in a fragmented landscape.