por The types of speciation The main ones are allopatric, parapratic, stasipatric and sympratic. Speciation is the process in which new species arise from existing ones.
The most commonly used criterion to talk about speciation is spatial or geographical. The appearance of genetic differences between incipient species is the key element in speciation.
It is about the two separate groups of organisms coming to have differences that prevent or significantly hinder mating between them.
These differences can be as subtle as mating cycle disparities, for example, and may be caused by natural selection or genetic drift.
What are the types of speciation?
Up to now, we have talked about the following four types of speciation:
1- Allopatric speciation
It is also called geographic speciation, because it consists of the geographic separation of a group of living organisms so that two or more isolated populations result that do not mate with each other regularly.
This separation normally occurs for natural reasons such as migration, the extinction of geographically intermediate populations or geological events. That is to say, between the original group and the new one a geographical barrier arises that separates them.
This type of speciation occurs even when the «barrier» that hinders mating is violated by a few individuals from any of the groups.
This means that, even if there is gene flow between the two groups, if not on a considerable scale, we are facing allopatric speciation.
Example
The finches of the Galapagos Islands are usually given as an example of this type of speciation. On these islands there are different species of finches with a common continental ancestor.
Geographic or allopatric speciation can be divided into three types:
– Geographic or vicariant speciation
It is the classic allopatric speciation in which an ancestral species separates into two large groups that remain isolated until evolutionary independence appears, thanks to changes that occur to facilitate or allow local adaptation and geographic differentiation.
For example, the rise of the Isthmus of Panama was responsible for the speciation of the Alpheus genus of lobsters, which are located on each side of the isthmus.
– Speciation through peripheral populations or peripatric speciation
In this case, the new species emerges from the geographic margins of the territory in which the largest central population is found.
This is the case of a speciation that occurs after a dispersal and/or colonization process, where the adaptation to the new environment generates the differences but, because they are small groups, the greatest weight in these changes is carried by stochastic factors.
An example of this mode of speciation is reflected in the drosophila species in Hawaii, which become very numerous due to migration and diversification.
– Speciation in asexual organisms
It is the case in which history determines the identity of the species, and genetic drift becomes a very important evolutionary factor.
2- Parapatric speciation
In this mode of speciation, differentiation occurs even when there is not complete geographic separation of the groups.
In this case, although the original population is close, the mating is not random due to some subtle variation in the characteristics of some of its members.
Example
To better understand this mode of speciation, the example of some grasses that have grown near a mine is given.
Those closest to the mine have developed a tolerance to heavy metals, while their neighbors have not. This has caused their flowering times to be different and, therefore, they cannot mate.
It is difficult to differentiate this speciation from the allopatric, which is why many question its presence within the classification.
3- Stasipatric speciation
This type of speciation has been considered by many as a post-colonization speciation, in which evolutionary independence appears due to chromosomal mutations.
In this speciation, a chromosome mutation allows a group to colonize more easily.
Such mutations are fixed in small groups with little migration and a new species arises, very similar to the original and, in fact, will occupy the same range of distribution.
Example
Australian grasshoppers of the genus Vandiemenella are a clear example of this speciation, given the stability of their distribution over the years.
4- Sympatric speciation
This type of speciation does not imply large-scale geographic separation between populations, but rather that one of the groups uses a different ecological niche within the distribution range of the original species. Thus, reproductive isolation arises.
Example
An example of speciation is the apple fly. Gene flow has decreased in these species, even though they live in the same geographic region.
Another type of sympatric speciation involves the formation of an asexual species from a sexual precursor species. This type of speciation has a variant that occurs due to specialization, normally due to adaptation to a resource.
An example of this case is that of the fruit fly (Rhagoletis pomonella) that mates on the fruits of some plant species, called hosts in this case, but whose larvae develop inside the fruit.
Several species within this fly genus have switched hosts.
This speciation appears to be common among parasitic species and in aquatic organisms in lakes, such as African lake cichlids.
These speciation processes come to be the answer to the questions posed by evolutionary biology.
References
Biology Blog (2017). «Species and speciation»in Biology Blog. Retrieved from Biology Blog: blogdebiologia.com
Cuevas, E. (2013). «Mechanisms of ecological speciation in plants and animals» in Biological. Retrieved from Biologics: biologicas.umich.mx
Perfectti, Francisco (s/f). «Speciation: modes and mechanisms» at the University of La Rioja. Retrieved from the University of La Rioja: dialnet.unirioja.es
Spanish Society of Evolutionary Biology (s/f). «Modes of speciation» in Spanish Society of Evolutionary Biology. Retrieved from the Spanish Society for Evolutionary Biology: sesbe.org
Spanish Society of Evolutionary Biology (s/f). “Speciation modes” at Berkeley University of California. Retrieved from Berkeley University of California: evolution.berkeley.edu
wikipedia.org