The coevolution it is a reciprocal evolutionary change that involves two or more species. The phenomenon results from the interaction between them. The different interactions that occur between organisms - competition, exploitation and mutualism - lead to important consequences in the evolution and diversification of the lineages in question..
Some examples of evolutionary systems are the relationship between parasites and their hosts, the plants and herbivores that feed on them, or the antagonistic interactions that occur between predators and their prey..
Co-evolution is considered one of the phenomena responsible for the great diversity that we admire today, produced by interactions between species.
In practice, proving that an interaction is a coevolution event is not an easy task. Although the interaction between two species is apparently perfect, it is not reliable evidence of the coevolutionary process.
One approach is to use phylogenetic studies to test whether there is a similar pattern of diversification. In many cases, when the phylogenies of two species are congruent, it is assumed that there is coevolution between both lineages..
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Before delving into the issues related to coevolution, it is necessary to mention the types of interactions that occur between species, since these have very important evolutionary consequences..
Species can compete, and this interaction leads to negative effects on the growth or reproduction of the individuals involved. Competition can be intraspecific, if it occurs between members of the same species, or interspecific, when individuals belong to different species.
In ecology, the "competitive exclusion principle" is used. This concept proposes that species that compete for the same resources cannot compete in a stable way if the rest of the ecological factors remain constant. In other words, two species do not occupy the same niche..
In this type of interaction, one species always ends up excluding the other. Or they are divided into some dimension of the niche. For example, if two species of birds feed on the same thing and have the same resting areas, to continue coexisting they may have their peaks of activity at different times of the day..
A second type of interaction between species is exploitation. Here a species X stimulates the development of a species Y, but this Y inhibits the development of X. Typical examples include interactions between the predator and its prey, parasites with hosts, and plants with herbivores..
In the case of herbivores, there is a constant evolution of detoxification mechanisms in the face of the secondary metabolites that the plant produces. Similarly, the plant evolves into toxins more efficiently to drive them away.
The same occurs in predator-prey interaction, where prey constantly improve their ability to escape and predators increase their attack abilities..
The last type of relationship involves a benefit, or a positive relationship for both species that participate in the interaction. There is then talk of a "reciprocal exploitation" between the species.
For example, the mutualism between insects and their pollinators translates into benefits for both: insects (or any other pollinator) benefit from plant nutrients, while plants gain dispersal of their gametes. Symbiotic relationships are another well-known example of mutualism..
Co-evolution occurs when two or more species influence the evolution of the other. Strictly speaking, coevolution refers to the reciprocal influence between species. It is necessary to distinguish it from another event called sequential evolution, since there is usually confusion between both phenomena.
Sequential evolution occurs when one species has an effect on the evolution of the other, but the same does not happen in the reverse direction - there is no reciprocity.
The term was used for the first time in 1964 by researchers Ehrlich and Raven.
Ehrlich and Raven's work on the interaction between lepidoptera and plants inspired successive investigations of "coevolution." However, the term became distorted and lost meaning over time..
However, the first person to carry out a study related to the coevolution between two species was Charles Darwin, when in The origin of the species (1859) mentioned the relationship between flowers and bees, although he did not use the word "coevolution" to describe the phenomenon..
Thus, in the 60s and 70s, there was no specific definition, until Janzen in 1980 published a note that managed to correct the situation.
This researcher defined the term coevolution as: "a characteristic of the individuals of a population that changes in response to another characteristic of the individuals of a second population, followed by an evolutionary response in the second population to the change produced in the first".
Although this definition is very precise and was intended to clarify the possible ambiguities of the coevolutionary phenomenon, it is not practical for biologists, since it is difficult to prove.
Similarly, simple coadaptation does not imply a process of coevolution. In other words, the observation of an interaction between both species is not robust evidence to ensure that we are facing a coevolution event..
There are two requirements for the coevolution phenomenon to take place. One is specificity, since the evolution of each characteristic or trait in a species is due to the selective pressures imposed by the characteristics of the other species involved in the system..
The second condition is reciprocity - the characters must evolve together (to avoid confusion with sequential evolution).
There are a couple of theories related to coevolution phenomena. Among them are the hypotheses of the geographic mosaic and that of the red queen..
This hypothesis was proposed in 1994 by Thompson, and considers the dynamic phenomena of coevolution that can occur in different populations. In other words, each geographical area or region presents its local adaptations.
The migratory process of individuals plays a fundamental role, since the entry and exit of the variants tend to homogenize the local phenotypes of the populations.
These two phenomena - local adaptations and migrations - are the forces responsible for the geographic mosaic. The result of the event is the possibility of finding different populations in different coevolutionary states, since each one follows its own trajectory over time..
Thanks to the existence of the geographic mosaic, the tendency of coevolution studies carried out in different regions but with the same species to be inconsistent with each other or in some cases, contradictory can be explained..
The Red Queen hypothesis was proposed by Leigh Van Valen in 1973. The researcher was inspired by the book written by Lewis Carrol Alice through the mirror. In a passage in the story, the author tells how the characters run as fast as they can and still remain in the same place.
Van Valen developed his theory based on the constant probability of extinction experienced by lineages of organisms. That is, they are not capable of "improving" over time and the probability of extinction is always the same..
For example, predators and prey experience a constant arms race. If the predator improves its ability to attack in any way, the prey should improve to a similar extent - if this does not happen, they may become extinct.
The same occurs in the relationship of parasites with their hosts or in herbivores and plants. This constant improvement of both species involved is known as the Red Queen hypothesis..
The term "coevolution" includes three basic types. The simplest form is called "specific coevolution", where two species evolve in response to the other and vice versa. For example a single prey and a single predator.
This type of interaction gives rise to an evolutionary arms race, which results in divergence in certain traits or can also produce convergence in mutualistic species..
This specific model, where few species are involved, are the best suited to demonstrate the existence of evolution. If the selective pressures have been strong enough, we should expect the appearance of adaptations and counter-adaptations in the species.
The second type is called “diffuse coevolution”, and it occurs when there are several species involved in the interaction and the effects of each species are not independent. For example, genetic variation in the resistance of a host against two different species of parasites could be related.
This case is much more frequent in nature. However, it is much more difficult to study than specific coevolution, since the existence of multiple species involved makes experimental designs very difficult..
Finally, we have the case of "escape and radiation", where a species evolves a type of defense against an enemy, if successful it can proliferate and the lineage can be diversified, since the pressure of the enemy species is not so strong.
For example, when a plant species evolves a certain chemical compound that turns out to be very successful, it can break free from the consumption of various herbivores. Therefore, the lineage of the plant can be diversified.
Co-evolutionary processes are considered the source of biodiversity on planet earth. This very particular phenomenon has been present in the most important events in the evolution of organisms.
Next we will describe very general examples of coevolution events between different lineages and then we will talk about more specific cases at the species level..
One of the most important events in the evolution of life was the innovation of the eukaryotic cell. These are characterized by having a true nucleus delimited by a plasma membrane and presenting subcellular compartments or organelles.
There is very robust evidence supporting the origin of these cells through coevolution with symbiotic organisms that gave way to current mitochondria. This idea is known as endosymbiotic theory..
The same applies to the origin of plants. According to the endosymbiotic theory, chloroplasts originated thanks to a symbiosis event between a bacterium and another larger organism that ended up engulfing the smallest.
Both organelles - mitochondria and chloroplasts - have certain characteristics that are reminiscent of bacteria, such as the type of genetic material, circular DNA, and their size..
The digestive system of many animals is an entire ecosystem inhabited by extremely diverse microbial flora.
In many cases, these microorganisms play a crucial role in the digestion of food, aiding in the digestion of nutrients and in some cases they can synthesize nutrients for the host..
In birds there is a very particular phenomenon, related to the laying of eggs in other people's nests. This coevolution system is made up of the crialo (Clamator glandarius) and its host species, the magpie (Pica pica).
The laying of the egg is not done randomly. In contrast, the calves choose the pairs of magpies that invest the most in parental care. Thus, the new individual will receive better care from their adoptive parents..
How do you do it? Using cues related to host sexual selection, such as a larger nest.
In response to this behavior, magpies decreased their nest size by almost 33% in the areas where the young exist. Similarly, they also have an active defense of nest care.
The brood is also capable of destroying the magpie's eggs, to favor the rearing of its chicks. In response, magpies increased the number of eggs per nest to increase their effectiveness..
The most important adaptation is being able to recognize the parasitic egg in order to expel it from the nest. Although parasitic birds have developed eggs very similar to that of magpies.
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