Coevolution — Definition & Examples

What Is Coevolution?

It is when two (or more) species affect each other's evolution. It is caused by symbiotic relationships and predator-prey dynamics.

A Classic Example:

The mutualistic relationship between acacia plants and acacia ants (genus Pseudomyrmex) is a form of symbiosis.

The horn of the bull horn acacia is a hollow thorn. A young queen ant will chew a hole in the thorn and start laying eggs inside. The spiky thorn not only helps protect the plant from herbivores, but it also protects the colony from predators. The acacia also provides nectar and little packets of proteins and fats for the ants.

So, if the acacia provides a home and food for the ants, what does it get in return? Well, you might be surprised: unlike most insect-plant symbiotic relationships, it's not pollination.

The answer is: protection. The ants bite any animal that comes too close to their plant. Not only do the ants protect the acacia plant from herbivores, they also pull up any new sprouts around the plant, preventing other plants from growing near the acacia.

However, not all biotic interactions can be mutually beneficial (+/+). Coevolution can also be caused by other interspecific relationships.

Many predator-prey and parasite-host pairs are continuously adapting and evolving in response to each other. This type of dynamic is sometimes called a coevolutionary arms race because both sides have to continuously adapt just to stay ahead of each other, or they risk going extinct.

Summary of Coevolution

Coevolution happens when the evolution of one species depends on the evolution of another species. The behavior of one species puts selective pressure on the other, and vice versa.

This happens when two or more species have close relationships within their ecosystems, including predator and prey or parasite and host.

The species enter something like an evolutionary race.

One common example is the relationship between some species of birds and butterflies.

Many birds feed on butterflies, but they tend to avoid some kinds which are poisonous or taste bad. The Monarch is a great example of this because it feeds on milkweed as a caterpillar, making it taste bitter.

To avoid being eaten by birds, some butterflies evolved to look more like the Monarch. This creates problems for birds, which have to get better at spotting the differences between the two. It also makes it more likely that the Monarch will accidentally be eaten, driving it to evolve away from the mimic.

Of course, this is just one example. In nature, many species also have a mutualistic relationship which drives coevolutionary changes. This is very common with flowering plants and the insects that pollinate them.

How Can Species Coevolve?

Coevolution is when two or more species have reciprocal evolutionary development. Over time, species evolve through natural selection in response to each other. The prefix co- means together, so the word literally means evolving together.

The results of the coevolutionary process can be seen in most biotic interactions today. All of your favorite interspecific interactions (inter-specific means between different species) like predator-prey and symbiosis can cause two or more species to coevolve. Even competition for resources between species can lead to this evolutionary dependence on one another.

Examples:

Many flowering plants have a close relationship with pollinating insect species. For example, bees and flowers have evolved to have a close symbiotic relationship: bees get nectar and pollen from flowers, which they use to make into food for the bee colony. While bees fly around collecting pollen, they are helping the flowers reproduce by spreading pollen from flower to flower. Plants and insects pollinating them are in general classic examples of mutualism (symbolized as $+/+$) where both parties involved are benefiting. Examples like this exist for other interactions, like parasitism and commensalism, as well.

An extreme example of coevolution between insect and plant species is the symbiotic relationship between the ficus (fig tree) and fig wasp. There are around 800 species in the Ficus genus, and every species of Ficus has a corresponding species of fig wasp specifically to pollinate it. How crazy is that?

Ficuses require fig wasps to pollinate them in order to reproduce. Male fig wasps spend their entire lives inside of the fruit. The female wasp only emerges from the fig she was born in to fly to another tree, where she will crawl into a developing fig, lay eggs, and die. The ficus-fig wasp relationship is an example of obligate mutualism, where both species have to (are obligated to) rely on the other to survive.

Predator-prey interactions are a great way to illustrate how two species that affected each other's evolutionary development in the past can still be continuously adapting and coevolving together.

When predators and prey (and parasites and hosts) coevolve, it is sometimes referred to as an evolutionary arms race, where each species continuously has to keep evolving new adaptations just to stay ahead of the other.

To Recap: A Quick Summary

Basically, any of the cool species-species interactions you can think of are a result of species adapting together over evolutionary time. The only biotic interactions that are not tied to coevolutionary mechanisms are things like invasive species, where the species has recently arrived in a new environment.

Interacting species put selective pressure on each other, which means they will also continue to evolve in response to each other.

(Video) Coevolution

by Brightstorm

This video above defines and explains coevolution, a pattern of evolution where two species develop behaviors or bodies that benefit one another.

One common and easily observable example is between bees and flowers. Bees depend on flowers for food, and flowers depend on the bees to pollinate them. Essentially, the bee allows some plants to reproduce.

As you can imagine, if the plant changes even slightly in a way that makes it harder for bees to get the pollen, the bees will need to adapt. Similarly, if the bees change their behavior, the flowers need to adapt to still attract the bees.

Any species that commonly interact with one another in the natural world can coevolve. This could happen when the two species help one another survive, as in the case of flowers and bees. It could also happen when two different species compete for something, like a food source. In this case, the two species will need to continue evolving in order to stay in the game.