coevolution

Coevolution is the process by which two or more species reciprocally influence each other’s evolution through their sustained ecological interactions. Through reciprocal selection, genetic changes in one lineage alter the selective environment for the other, leading to corresponding adaptive responses. Coevolution can occur in antagonistic interactions, such as predator–prey, herbivore–plant, and host–parasite relationships, or in mutualistic associations, such as pollination, seed dispersal, and symbiotic relationships with microbes.

In antagonistic coevolution, improvements by one partner often impose new selective challenges on the other, potentially producing evolutionary arms races or cycles of escalation and counter-adaptation. The Red Queen hypothesis captures this idea, suggesting that continual adaptation is required to maintain relative fitness in a dynamic biotic environment. Mutualistic coevolution can foster cooperation and interdependence, sometimes leading to specialized, tightly integrated partner relationships and co-adapted traits.

Notable examples include pollination systems in which floral traits and pollinator morphologies become matched, figs and their wasps, and the legume–rhizobia mutualism that aligns nitrogen fixation with plant needs. Predator–prey interactions, such as the toxin-based arms race between garter snakes and toxic newts, illustrate coevolutionary dynamics in antagonistic contexts. Host–parasite relationships also exhibit reciprocal adaptation, shaping defenses and counter-defenses.

Researchers study coevolution via phylogenetic congruence between interacting groups, reciprocal selection experiments, experimental evolution, and genomic analyses to identify coadapted loci. Coevolution has broad implications for ecological communities and the diversification of interacting lineages.