The peripatric speciation, in evolutionary biology, it refers to the formation of new species from a small number of individuals that was isolated in the periphery of this initial population.
It was proposed by Ernst Mayr and is one of his most controversial theories in evolution. Initially, it was called speciation by founder effect, to later be called parapatric speciation.
The new species arise at the limits of the central population, which has a greater number of individuals. During the speciation process, the flow between populations can be reduced to the maximum, until it ceases to exist. Thus, with the passage of time, the peripheral population constitutes a new species.
In this speciation model, the dispersion and colonization phenomena stand out. As individuals scatter, they are exposed to selective pressures (for example, environmental conditions) different from the initial population that eventually lead to divergence..
Genetic drift seems to have a special role in the parapatric speciation model, since the isolated population is generally small and stochastic factors have a greater effect in populations with reduced sizes..
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According to Curtis & Schnek (2006), peripatric speciation is defined as “a group of individuals founds a new population. If the founding group is small, it may have a particular genetic configuration, not representative of that of the original population ".
This can happen if the population experiences a bottleneck (a significant reduction in the number of its individuals) or if a small number of individuals migrate to the periphery. These migrants can be made up of a single couple or a single inseminated female.
The same can happen when a population experiences a decline in size. When this reduction occurs, the area of distribution decreases and small isolated populations remain on the periphery of the initial population. Gene flow between these groups is extremely low or null.
This mechanism was proposed by the evolutionary biologist and ornithologist Ernst Mayr, in the mid-1950s.
According to Mayr, the process begins with the dispersal of a small group. At one point (Mayr does not clearly explain how it happens, but chance plays a crucial role) the migration between the initial population and the small isolated population stops..
Mayr described this model in an article that focused on the study of New Guinea birds. The theory was based on peripheral bird populations that differ greatly from adjacent populations. Mayr accepts that his proposal is mostly speculative.
Another influential biologist in evolutionary theories, Hennig, accepted this mechanism and called it colonization speciation..
Following the classification by Curtis & Schnek (2006) of the mechanisms of speciation proposed by these authors, there are three main models of speciation by divergence: allopatric, parapatric and sympatric. While the instantaneous speciation models are peripatric and polyploidy speciation.
Futuyma (2005), on the other hand, places parapatric speciation as a type of allopatric speciation - along with vicariance. Therefore, peripatric speciation is classified according to the origin of the reproductive barrier..
Mayr proposes that the genetic change of the isolated population occurs rapidly and the gene flow with the initial population is cut off. According to this researcher's reasoning, the allele frequencies at some loci would be different from those in the initial population, simply because of sampling errors - in other words, genetic drift..
The sampling error is defined as the random discrepancies between what is theoretically expected and the results obtained. For example, suppose we have a bag of red and black beans in a 50:50 ratio. By pure chance, when I select 10 beans from the bag, I may get 4 red and 6 black.
Extrapolating this didactic example to populations, it may be that the "founder" group that will be established in the periphery does not have the same allele frequencies as the initial population..
Mayr's hypothesis implies a substantial evolutionary change that occurs rapidly. Furthermore, as the geographical location is quite specific and limited, coupled with the time factor, it would not be documented in the fossil record..
This statement tries to explain the sudden appearance of the species in the fossil record, without the expected intermediate stages. Therefore, Mayr's ideas anticipated the theory of punctuated equilibrium, proposed by Gould and Eldredge in 1972..
Not all living organisms seem potential candidates for peripatric speciation to produce a change in their populations.
Certain characteristics, such as low dispersal capacity and more or less sedentary life, make some lineages prone to groups so that this speciation model can act on them. Furthermore, organisms must have a tendency to structure themselves into small populations..
In the Hawaiian archipelago it is formed by a series of islands and atolls inhabited by a large number of endemic species.
The archipelago has drawn the attention of evolutionary biologists for the almost 500 species (some endemic) of the genus Drosophila that inhabit the islands. It is proposed that the immense diversification of the group occurred thanks to the colonization of a few individuals on nearby islands.
This hypothesis has been corroborated by applying molecular techniques to these Hawaiian populations..
Studies have revealed that the most closely related species are found on nearby islands and species that have recently diverged inhabit the new islands. These facts support the idea of a peripatric speciation.
The lizard of the species Uta stansburiana It belongs to the Phrynosomatidae family and is native to the United States and northern Mexico. Among its most outstanding characteristics is the existence of polymorphisms within its populations.
These populations represent a good example of peripatric speciation. There is a population that inhabits the islands of the Gulf of California and varies widely compared to their counterparts in the United States..
Island individuals differ widely in various characteristics such as size, coloration, and ecological habits..
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