Coevolution

Coevolution is reciprocal evolutionary change between interacting species, driving arms races between antagonists and mutual adaptation between partners.

Definition

Coevolution is the process by which two or more interacting species exert reciprocal selective pressures on one another, so that evolutionary change in one drives change in the other. It encompasses both antagonistic interactions, such as predator and prey, and mutualistic ones, such as plant and pollinator.

Scope

This topic covers antagonistic coevolution in predator-prey and host-parasite systems, mutualistic coevolution such as between plants and pollinators, the Red Queen dynamic of perpetual reciprocal change, and the geographic mosaic that produces variation in coevolutionary outcomes across landscapes.

Core questions

• How do reciprocal selective pressures drive coevolutionary arms races?
• How does coevolution shape mutualisms such as plant-pollinator relationships?
• What is the Red Queen hypothesis and how does it relate to coevolution?
• Why do coevolutionary outcomes vary geographically across a species' range?

Key theories

Coevolutionary arms races

Antagonistic species, such as parasites and hosts or plants and herbivores, impose reciprocal selection that drives escalating adaptation and counter-adaptation over time.

Geographic mosaic of coevolution

Because the strength and direction of interactions vary across space, coevolution produces a shifting mosaic of locally adapted populations with hotspots and coldspots of reciprocal selection.

Mechanisms

Coevolution occurs when the fitness of one species depends on traits of another, so each becomes a selective agent on the other. In antagonistic interactions, defenses and counter-defenses escalate in an arms race, as when plants evolve chemical defenses and herbivores evolve detoxification. In mutualisms, partners evolve traits that enhance the exchange of benefits, sometimes producing tight matching such as flower and pollinator morphology. The Red Queen dynamic describes continual reciprocal change required just to maintain relative fitness, important in host-parasite systems and the maintenance of sex. Because interactions vary geographically, coevolution generates a mosaic of locally divergent outcomes.

Clinical relevance

Host-parasite coevolution underlies the ongoing evolution of pathogen virulence and host resistance, the emergence of new infectious diseases, and the coevolutionary dynamics between immune systems and rapidly evolving pathogens, all central to infectious-disease biology.

History

Ehrlich and Raven's 1964 study of butterflies and plants popularized coevolution, and Van Valen's 1973 Red Queen hypothesis framed perpetual reciprocal change. Thompson's geographic mosaic theory, synthesized in 2005, emphasized spatial variation as a central feature of coevolutionary dynamics.

Debates

How tightly do species coevolve?

The degree to which interacting species coevolve in a specific, reciprocal manner, versus responding diffusely to many partners or to the broader environment, is debated across different interaction types.

Key figures

• Paul Ehrlich
• Peter Raven
• Leigh Van Valen
• John Thompson

Seminal works

• thompson2005
• ehrlichRaven1969
• futuyma2017

Frequently asked questions

What is the Red Queen hypothesis?

It is the idea, named after the character in Through the Looking-Glass, that species must keep evolving just to maintain their relative fitness against continually evolving competitors, predators, and parasites; coevolution can thus drive constant change without net progress.

Is coevolution always antagonistic?

No. Coevolution includes both antagonistic interactions, such as host-parasite arms races, and mutualistic ones, such as the reciprocal adaptation of plants and their pollinators for shared benefit.