Coevolution is the process in which two or more species influence each other's evolution over many generations. It matters because species do not evolve in isolation, since predators, prey, parasites, hosts, competitors, and mutualists all create selective pressures. These interacting pressures can shape body form, behavior, physiology, and life cycles.
Coevolution helps explain why nature often shows close matches between traits, such as long flower tubes and long pollinator tongues.
Key Facts
- Coevolution occurs when evolutionary change in species A changes selection pressure on species B, and species B then changes selection pressure on species A.
- Natural selection acts on heritable variation, so coevolution requires genetic differences that affect survival or reproduction.
- Predator-prey arms races can favor faster prey, better camouflage, stronger toxins, sharper senses, or improved hunting strategies.
- Host-parasite coevolution often follows a Red Queen pattern, where both sides must keep adapting just to maintain relative fitness.
- Mutualistic coevolution can increase the fit between partners, such as flower shape matching pollinator body parts.
- Change in allele frequency can be described by Δp = p_after selection - p_before selection.
Vocabulary
- Coevolution
- Coevolution is reciprocal evolutionary change between interacting species caused by selection pressures they place on each other.
- Selective pressure
- A selective pressure is an environmental or biological factor that affects which traits increase survival or reproduction.
- Arms race
- An arms race is a coevolutionary pattern in which opposing species repeatedly evolve stronger defenses and counter-defenses.
- Mutualism
- Mutualism is an interaction in which both species benefit, such as a plant receiving pollination while an insect receives nectar.
- Red Queen hypothesis
- The Red Queen hypothesis states that interacting species may need continuous adaptation to keep up with each other.
Common Mistakes to Avoid
- Saying one species chooses to evolve a useful trait is wrong because evolution depends on heritable variation and differential reproduction, not conscious choice.
- Calling any close interaction coevolution is wrong because coevolution requires reciprocal evolutionary change, not just one species affecting another ecologically.
- Assuming coevolution always helps both species is wrong because predator-prey and host-parasite coevolution often benefits one species while harming the other.
- Using a single individual as evidence for coevolution is wrong because evolution is measured as changes in populations across generations.
Practice Questions
- 1 In a host population, an allele for parasite resistance has frequency 0.20 before a disease outbreak and 0.35 after several generations of selection. Calculate Δp for the resistance allele.
- 2 A flower species has 120 plants. Pollinators successfully visit 84 plants with long floral tubes and 36 plants with short floral tubes. What percentage of successful visits are to long-tube plants?
- 3 A new parasite evolves the ability to infect a common host defense type. Explain how this could change selection pressures on both the host population and the parasite population over future generations.