The co-evolutionary genetics of ecological communities

Co-evolutionary genetics of ecological communities offers a new understanding of adaptation and gene function that cannot be obtained from genomic data without an ecological context.Some interspecific interactions, such as those that involve host and pathogen or predator and prey, can be intensified by reciprocal co-evolution, whereas other interactions, such as competition over limiting resources, can be diminished by reciprocal co-evolution.Molecular phylogenetics offers an historical context for studying species interactions, providing evidence for co-speciation and the means for distinguishing co-speciation from other processes, like duplication or host switching.Genotype-by-environment interactions (G x E) have a central role in co-evolution. They have given rise to many unique co-evolutionary adaptations, such as the inducible defenses of many prey species, which are textbook cases of adaptive phenotypic plasticity and developmental switching.Under some circumstances, G x E increases genetic diversity in both species that interact with each other. This kind of interspecific G x E holds the potential to be an engine of biodiversity by accelerating co-evolution and facilitating the co-speciation of hosts and pathogens, whenever ecological communities are subdivided and gene flow among them is reduced.The same genetic theory that was used to describe the evolution of epistatic interactions (interactions between nuclear genes at different loci) can be used to describe the co-evolution of interacting species. Recognizing that co-evolution affects gene combinations between species (that is, interspecific epistasis), epistasis theory can be applied to co-evolution in ecological communities. Just as reductions in recombination facilitate selection on gene combinations, co-dispersal of hosts and symbionts facilitates selection on interspecific gene combinations and leads to a high degree of interspecific cooperation, as in reciprocal obligate symbioses.The co-evolution of mitochondrial–nuclear gene combinations is a model to study the co-evolution of interspecific gene combinations.