Definition: a new species evolve from a single ancestral species while inhabiting the same geographic region
Table of Contents
Speciation is a process of evolution through which two different existing populations evolve and a distinct species form. It is a process in which two populations become genetically different. The ways in which new species are formed are as follows: (1) allopatric speciation, (2) peripatric speciation, (3) parapatric speciation, and (4) sympatric speciation.
Sympatric Speciation Definition
Sympatric speciation refers to a speciation process when two groups of identical species lived in identical geographical areas, they evolve in such a way that they could no longer interbreed. At that point, they are considered to be different species. It is also the reason to explain the formation of two or more genera from the same ancestral species in the same geographic area. Although this type of speciation can be seen in many different organisms such as apple maggot fly, bacteria, and cichlid fish it is hard to tell when it occurs naturally.
Sympatric speciation is distinctive as it occurs when two populations of the same species are found in the same territory but are able to split into two different groups and genetically develop so differently that they can no more interbreed and become different species.
Sympatric Speciation Examples
Apple maggot fly
For example, the insect, Rhagoletis pomonella (apple maggot fly), is an example of sympatric speciation. Initially, the apple maggot flies lay their eggs on hawthorn fruit (a relative of apple). In the 19th century, a distinct form of maggot fly emerged that lay eggs on apples only. This happened when apples were brought to North America. So now, two distinct groups of apple maggots are found: one laying eggs on apples and the other laying eggs on hawthorns.
The female lays her eggs on the fruit where it grew; the male seeks and mates with the female on the same fruit, also, on where it grew. As a result, hawthorn-grown flies will produce offspring in hawthorn fruits alone, and apple-grown flies will raise offspring in apple fruits alone. Therefore, there is an alteration in the genetic makeup of both groups and by the passage of time they will come out as different species. This example shows that speciation is even possible in the same species having different groups but in the same geographical area.
The Midas cichlid (species of Amphilophus), which is living in Lake Apoyo (a volcanic lake in Nicaragua), is an example of sympathetic speciation. Scientists analyze their appearance, nature, and DNA. Although these two have similarities they are different as well and cannot cross-breed. All the available evidence indicates that one species evolved from another. The newer species of this population has evolved almost recently but if we talk about the terms of evolution, it evolved almost 10,000 years back.
The divergence of “resident” and “transient” orca forms in the northeast Pacific is an uncommon example of sympatric speciation. Despite living in the same water, orcas avoid each other and do not interbreed. They are different in many ways like having different diets, vocal behavior, and social structure. They also attack different prey. A remarkable reduction in the population occurs almost 200,000 years back which not only reduces the size of the population but also affects gene variation. After that numerous ecotypes emerged.
In bacteria, sympatric speciation is supposed to occur more frequently. Bacteria can exchange genes with others that are neither parent nor offspring. This is done by a method known as horizontal gene transfer. Sympatric speciation has been observed in Synechococcus and Bacillus species of bacteria, and also in the bacterioplankton Vibrio splendidus. It is considered that adaptation to environmental conditions is one of the important factors in sympatric speciation. If some members are adapted to live in a certain environment and a small group of those species can move to a new location then they will eventually adapt to that new environment.
allopatric speciation, peripatric speciation, peripatric speciation
Types of Speciation
Geographically there are four different natural ways by which speciation occurs. These are:
- Sympatric Speciation
- Allopatric Speciation
- Peripatric Speciation
- Parapatric Speciation
In allopatric speciation, because of population dispersion or a natural geologic event one species gets separated into different groups, and then they are divided into two different species. The geologic event can be the formation of mountains. Like the other types of speciation, allopatric speciation is typically a very slow process.
Allopatric speciation usually takes place when the species is divided into two different classes or groups. Mountain ranges, waterways, or any other physical barriers make interbreeding difficult. Each species, then, grows differently, adapting eventually according to its environment. They, then, pass the characters or traits to the next generation.
Ways of allopatric speciation:
- Members of a population get separated because of any geographical event. That event either be the formation of any waterway or any mountain range. The activities of humans such as cutting down of the forest and land pollution affect the natural habitat of many species. The destruction of their habit causes them to migrate.
- Mutation in genes will cause diversity in the characters of the population. Genetic variations will lead to the emergence of new and different characters among the species of a population, which will ultimately lead to diverging populations.
When members from the population of plants, animals, or any other organism get separated and stop exchanging genetic material from the members of the same species then they are said to be geographically isolated. Any accident or coincidence will cause geographical isolation. It can also be caused by many other factors and will lead to different results. Some examples are below:
- Isolation by barriers: physical barriers prevent the fishes of two different pools from interbreeding. It will lead to a less varied gene pool among the fishes. Soon, the fish will not be able to mate with the members of other groups which will cause less variation in the gene pool.
- Isolation after an event: two populations might get separated from each other due to any natural disaster like an earthquake. And then, each species would have different genetic makeup; this will lead to less diversity. A fire in the forest causes the separation of some animals, e.g., deer, from its main group. Over time this small group interbreeds and develops into a separate or distinct species with different genetic makeup.
- Isolation by separation: individuals in small and isolated towns do not marry any person who is outside of the town. This will not only lead to less variation in the gene pool but also causes a homogenous population.
- Isolation by distance: when a flock of finches gets isolated from the main group, there is limited or no genetic exchange and ultimately the isolated group will become a new species. Bottlenose dolphins get separated from their main group and do not withstand the ecological changes and in the end, got extinct.
On the formation of the Arizona Grand Canyon, small mammals, like squirrels, that were once part of the same population could no longer communicate and inter-breed with each other due to the barrier. So, by the passage of time, the squirrels face allopatric specification and now two distinct types of squirrels live on the north and south edges of the canyon. Kaibab squirrels are at the north edge of the canyon while Abert squirrels are at the south edge. Although these two species are identical in size, shape, diet and have slight color variation they are neither in contact with each other nor cross-breed. That’s why both are considered separate species.
Parapatric speciation occurs in a small group of the same population that are isolated from each other but there is a fine and narrow range in which their ranges overlap. This happens because there is an uneven distribution of members of the subpopulations or a limited geographic barrier. This can occur among numerous subpopulations that are next to each other. In this way, the populations close to each other can cross-breed. There are slight differences in members of a subpopulation; because of these differences, the members at the extreme ends could not cross-breed. Species from this type of speciation are also referred to as the ring species.
In parapatric speciation, as the species are dispersed widely over an immense region, they have most likely the chance to interbreed with each other but the members could only prefer to interbreed with those members which are in their geographic area. In parapatric speciation, the physical barrier does not separate the species but they get isolated by their variations in the same environment.
Sometimes parapatric speciation occurs because of polluted and contaminated habitat. There is a high level of metals such as lead and zinc because of mining activities that get absorbed in the soil and affect the growth of certain plants. For example, Buffalo grass (also known as vanilla grass) is found in Asia and Europe. It was also found in North and South America. The buffalo grass could not survive in soil having metals. Over time adaptation develops and now it can tolerate metals and the seeds pass this character to the next generation also.
Peripatric speciation takes place in a large population, when the members on the boundary or at the periphery get separated from the main group and, with time, form a separate species.
It is difficult to distinguish peripatric speciation from allopatric speciation. In the allopatric speciation, members of the group could not interbreed because of physical barriers. The main differentiating point between allopatric speciation and peripatric speciation is that in peripatric speciation one group is smaller than the other. The distinctive features of small groups transferred to the following generation which then becomes their exceptional and unique traits.
Peripatric speciation usually takes place when the smaller group of the population gets separated and goes to a different ecological environment and starts living in a different environment and eating different food. As the separated group is generally small, there might be an effect on the proportion of some characters of the new population as compared to the old ones.
Let’s consider a community of birds. Most of them are blue and some are red. The red group which is the smaller one gets isolated from the larger blue group. Now the next generation of the smaller group will also be red, which is a different trait from the main blue group. Such modification in gene frequency is known as Genetic Drift. With the passage of time, many changes will occur and red birds will arise as completely different species.
Artificial speciation is another type that emerged recently. It is the formation of new species by a human. The formation of new species can be achieved through lab experiments. Mostly the scientists doing research on insects like fruit flies.
Allopatric vs. Sympatric Speciation
What is the difference between allopatric and sympatric speciation? One main difference is that geographic isolation led to the formation of new species in allopatric speciation. As for sympatric speciation, the two species live in the same geographic region and yet do not interbreed, thus, caused their divergence. The table below shows a summary of the difference between allopatric speciation and sympatric speciation.
|Allopatric Speciation||Sympatric Speciation|
|Definition||It is the physical isolation of the biological population by any external barrier that caused the reproductive isolation||It is the evolution of a new species from a single ancestral species while living in the same habitat|
|Differentiation Mechanism||Natural Mechanism||Polyploidy|
|Speed of Emergence of new species||Slow||Fast|
|Example||Darwin Finches |
Squirrels in Grand Canyon
|Cultivated Wheat, corn |
Sympatric Speciation in Evolution
What is sympatric speciation in evolution? In 1859, Charles Darwin’s ‘Origins of Species’ had an impact on the evolutionary world of biology. According to the observation of Darwin, evolution is a very slow process when it is done through the mechanism of natural selection. He assumed that new species could be the result of this mechanism but evolution takes time. He also sketches in his diary about 20 years ago the publication of Origins of Species. The sketch is shown below.
Darwin proposed that species could form in two ways:
- Evolution of one species splitting into two
- Population diverging from its extant ancestor to a new species.
How does sympatric speciation occur? Sympatric speciation occurs when all the members are in close association with one another, interbreed with each other, and there is no physical boundary or obstruction stopping the members. Naturally, a new species can develop, based on contrasting characters and food supply. The logic is that some members adapt to their environment and become dependent on their food and shelter while some do not.
It can also occur through disruptive selection, i.e., natural selection. For example, a population of herbivorous insects lives in the same area but feeds on two different types of plants. If this change lasts longer then it will result in the formation of two different subpopulations having their specialized characters.
Gene Flow and Sympatric Speciation
The movement of genes into or out of a population is known as gene flow. The members of two populations can transfer or share their genetic makeup by interbreeding. This will not only minimize the differences but also makes the gene pool less diverse.
Gene flow typically is reduced via immigration (entering of new members in the population) and emigration (leaving of members from the population). Through large-scale geographic distance, a population could eventually gain or lose alleles. Gene flows greatly affect small populations because individuals of a small population might be carrying a particular allele and the allele will be lost if they leave the population while it is unlikely to happen in a large population because the other members still have the same allele. Gene flow results in the introduction and loss of alleles whenever the members immigrate or emigrate.
However, as for sympatric speciation where speciation occurs not by geographic isolation or physical separation, gene flow may still be reduced. How? The emergence of a new niche is one huge factor causing them to speciate despite living in the same geographical range.
What prevents speciation from occurring in sympatric populations? A population is described as sympatric when the two related populations thrive in the same area. Speciation may not occur if reproductive isolation does not occur or if it does, will not last too long that the two groups eventually speciate. Speciation can take place only when interbreeding among two sub-populations halts which means a natural reproductive obstacle is present. As long as random interbreeding among all members lasts, sympatric speciation will not take place. The populations can interbreed freely as long as they frequently encounter in the geographic area and the conditions of the environment remain roughly constant. There are no special pressures for the selection of any specific trait that causes the gene pool to diverge into different populations.
Try to answer the quiz below to check what you have learned so far about Sympatric Speciation.
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