Evaluating the role of coevolution in a horizontally transmitted mutualism

We tested the hypothesis that coevolution underlies the persistence of horizontally transmitted mutualisms. Specifically, we assessed the roles of pairwise and diffuse coevolution by testing for specialization within and across host species with their mutualistic symbionts. We tested our hypothesis by leveraging the interaction between the squash bug Anasa tristis and its horizontally transmitted bacterial Caballeronia spp. symbionts.