Sympatric speciation: what it is, definition and fundamentals

It is estimated that, up to the year 2014, a total of 1,426,337 animals have been discovered on our planet. This value fluctuates almost daily, since it is also estimated that there are almost a total of 8 million species of living beings, of which more than ¾ are waiting to be discovered.

On the other side of the coin, the UN reports that around 150-200 species become extinct every 24 hours, a fact that offsets the 20,000 discovered on average annually. All these figures indicate an undeniable truth: the biological reality of our planet is fluctuating and, since we are in it, the number and characteristics of the living beings that accompany us have changed drastically.

All this genetic and behavioral variability on the planet cannot be explained without concepts such as natural selection and drift. genetics, facts that promote the presence or disappearance of species over time, as well as changes in their mechanisms adaptive. Today we are going to explain what it is sympatric speciation, the phenomenon that is presumably the most important driver when it comes to the appearance of new species

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• Related article: "Allopatric speciation: what it is, types, characteristics and examples"

How do new species appear?

From a biological point of view, A species is defined as a group of individuals who are fully fertile among themselves, but isolated from interbreeding with other similar groups. for its physiological properties. If we go to a slightly more evolutionary description, we can say that a species is a single line of populations. ancestor-descendants that maintains its identity with respect to other lines and preserves its own evolutionary tendencies and destiny historical.

In short: a species is made up of one or several populations of living beings that can reproduce each other, give rise to fertile offspring and that, in addition, present a clear phylogenetic lineage, sharing an ancestor common. Seems like a pretty tight definition, right? How can new species appear then?

The mechanisms of speciation

Speciation is known as the process by which a population of a certain species gives rise to another or other populations, reproductively isolated from the original that, after a certain time, they accumulate enough genetic differences that they cannot conceive fertile offspring with the original population.

Ernst Mayr, a renowned evolutionary biologist of the 20th century, postulated that there are two major mechanisms of speciation:

• Phyletic evolution: when an E1 species, over a long period of time, becomes an E2 species due to genetic changes.
• Evolution by cladogenesis: also known as bifurcation, in this case a primordial species originates two or more derivatives through a process of divergence.

So that we understand each other, in phyletic evolution the original species disappears to give rise to a new one, while in the cladogenesis variant the original does not have to disappear, but rather "forks" into new taxa by differentiation through different mechanisms.

What is sympatric speciation?

It is evolution by cladogenesis that interests us, since For this bifurcation to occur between two populations of a species, a barrier must first appear that prevents them from being in contact. Allopatric speciation is the clearest representation of this process because, in it, a barrier literally appears geography (a river, a mountain or a separation of tectonic plates, for example) that makes contact between the two impossible populations.

Sympatric speciation is a little more difficult to understand, since in this case there is no barrier tangible and observable in the first instance that makes contact between individuals of the same species impossible and population. Different mechanisms are postulated by which these “non-physical” isolates can appear and, among them, are the following.

1. Sympatric speciation by specialization: a clear example

We do not want to enter into genetic conglomerates but, in a very general way, we can say that this postulation is based on the fact that there may be alleles for a gene that encode more or less successful behaviors in the face of certain events. For example, a population of insects may have an A1 allele that specializes them to consume certain plants, while the mutation of the A2 allele turns out to be more effective when it comes to preying on other animals.

As this genetic information is inheritable from parent to offspring, and under certain conditions, A2 individuals can be expected to end up presenting a sufficient behavioral differentiation with respect to the A1 to give rise to different species after a long period of time. Both populations will end up exploiting different niches and accumulating highly diverse adaptations, which is why which does not require a physical space that produces geographic isolation to give rise to two species different.

2. Polyploidy and hybridization

These events are very common in the world of plants, but they also occur in animals. In the case of polyploidy, we are talking about an increase in the number of chromosomes in a population at the cellular level. For example, meiosis causes the formation of haploid cells (n), which are the eggs and sperm, whose fusion will give rise to a diploid (2n) zygote, as we humans are in all but the cells sexual.

If normal disjunction does not occur during meiosis, the sex cells will be diploid (2n) and therefore the zygote or individual born will be tetraploid (4n). As you can imagine, these descendant individuals will be reproductively isolated from their parents and from the original population, but they will be able to reproduce among themselves.

As far as hybridization is concerned, in this case a new individual can be produced from parents of two different species.. Most hybrids in the animal kingdom are sterile but, especially in the case of plants, sometimes these they can be reproductively viable between them but cannot reproduce with either of the two species parental. Thus, from a theoretical framework, a new species would also emerge.

• You may be interested in: "Ecological niche: what it is and how it helps to understand nature"

3. Speciation by change of type of reproduction

The appearance of asexual lines from sexual lines in the same population automatically leads to evolutionary independence., which is why this mechanism can be considered a type of instantaneous sympatric speciation.

There are cases of lizards and salamanders in which this type of speciation has been documented, since once the route is chosen asexual, in some cases it is no longer necessary to exchange genetic information that reproduction entails with the population primal. Again, all this is much more observable and common in plants than in the rest of the phyla.

4. Sympatric speciation by disruptive selection

In this case we are talking about something very similar to sympatric speciation by specialization, but some meanings can be made with respect to this term. Disruptive selection promotes that, in the same population, some individuals adapt to exploit a niche, while others take a completely different path.

For example, let's say that in a population of birds their prey begins to disappear from the environment for X or Y reasons, since ecosystems are not watertight. Faced with this need, and at least on paper, one would expect that one group of this population would move away from the other at a level behavioral to promote the permanence of the species and that the individuals of the same do not "step on" their needs among they. Thus, some birds could adapt to hunting at night and others during the day.

You can already imagine all that this entails: basically, the individuals of the same population would hardly come into contact at all: some would live during the day and others at night. In the end, the number of diverse adaptations and reproductive isolation is such in both populations that, in the same space, two species end up emerging without any physical barrier.

Summary

In the foundations of evolutionary biology lies the conception that allopatric speciation (remember: differentiation of two populations by a geographical barrier) is the most important speciation mechanism, since basically it is the one that can be observed in a tangible way through the eyes humans. With the advancement of science and the development of genetic tests, many 20th century biologists have been found to be quite wrong.

Today, it is considered that sympatric speciation explains biological variation much better than allopatric, since there are many reproductive isolation mechanisms that do not pass through a tangible physical barrier. This is not to say that allopatric speciation has not done its job over the centuries, but rather that its importance has probably been overestimated.

We hope that sympatric speciation has become clear to you along these lines, since we are dealing with a phenomenon that is somewhat difficult to understand, since it occurs through unobservable mechanisms. If we want you to keep an idea of ​​all this hypothetical and terminological conglomerate, this is the following: sometimes a physical barrier is not necessary for two populations to differentiate into two species different. Simple as that.

Bibliographic references:

• Garcia, E. c. (2012). Mechanisms of ecological speciation in plants and animals. Biological Magazine of the DES Agricultural Biological Sciences, 14(2), 7-13.
• Gutierrez, L. m. h. biological speciation.
• Lasserre, D. F. Sympatric speciation and its genetic and morphological implications in fruit flies.
• Perfectti, F. (2002). Speciation: modes and mechanisms. Soler M., Evolution: The basis of biology. South Project. Spain.