What is the Difference Between Allopatric and Sympatric Speciation?

Introduction

Speciation is a process that leads to the formation of new biological species through evolution. The process has established that the cladogenesis splits, not the anagenesis. Indeed, the Speciation process has been categorized into two main sub-processes: allopatric and sympatric.

Allopatric Speciation

Eweleit, Reinhold, and Sauer (2015) aver that allopatric speciation is very common to detect. It happens whenever certain populations of a given species are isolated geographically. In such isolation, the gene flow between the species is usually hindered. The lack of gene flow between the species enhances the development of certain genetic identities that differentiate them from their previous counterparts. The new identity is usually obtained from the immediate environment that surrounds the species (Eweleit, Reinhold & Sauer, 2015). If the given populations are comparatively small, a founder effect may be experienced. For instance, a case where the populations held dissimilar allelic frequencies at the time they were being separated. Genetic and selection drift will act on a different level from these two backgrounds because they are different genetically, creating distinct genetic differences between the two new species. The formation of new species is usually guided by natural selection. According to Eweleit, Reinhold, and Sauer (2015), a place’s climate, predators, and resources determine the identity of the new species to a great extent.

A perfect example of allopatric speciation is witnessed in the Hawaiian honeycreepers, according to Frawley and Orr-Weaver (2015). These birds have undergone this type of evolution, more specifically, speciation. In fact, the birds’ beaks have evolved to suit the needs of the new environments that they have been forced to live in. Their beaks have evolved according to the food source in their new environments. For those isolated in areas with seeds, their beaks have become stronger and thicker, while those with nectar have beaks shaped like swords and are very long. It is through allopatric speciation that this has happened, whereby the birds with similar genes have become two different species due to geographical isolation.

Sympatric Speciation

According to Gras, et al. (2015), sympatric speciation is a type of speciation where the populations of a given species tend to be isolated in terms of reproduction processes even though they reside close to each other. As a result, this type of speciation is very rare. It has been observed mostly in plants rather than in animals. This speciation is because the process of self-fertilization is more common with plants than with animals. A good example is a tetraploid plant that can self-fertilize itself to create new offspring. For animals, self-fertilization is not achievable, and they have to look for an animal with the same genes, opposite sex, with random polyploidy.

It is worth noting that polyploidy aids sympatric speciation. The phenomenon of polyploidy is the process through which a group of offspring or an individual offspring is produced with many chromosomes as opposed to other offspring (Frawley & Orr-Weaver, 2015). In this aspect, the number of chromosomes usually doubles the normal amount. Even though having double chromosomes is typical, other offspring have more than twice. They are referred to as tetraploidy having four chromosomes. Polyploidy can be said to be the process that gives birth to sympatric speciation.

Gras, et al. (2015) indicate a perfect example of this type of speciation: the Orca forms found in the Pacific in the northeast area. These forms have undergone divergence based on this type of speciation to produce transient Orca forms and resident Orca forms. Consequently, these forms have undergone diploidy, doubling the number of normal chromosomes. They represent a perfect situation of sympatric speciation.

Polyploidy

The polyploidy process, as earlier mentioned, involves the production of offspring with more chromosomes than normal. Many scientists have identified the process as leading to reproductive isolation. Reproductive isolation usually leads to the inability to interbreed between organisms. Like sympatric speciation, polyploidy is more common in plants than animals (Frawley & Orr-Weaver, 2015). In fact, Angiosperms are considered polyploidy, with 60% of the world’s angiosperms being polyploidy. The perfect example of an angiosperm is a wheat seed with 42 chromosomes, which is thought to be a hexaploid (Eweleit, Reinhold & Sauer, 2015).

In animals, though polyploidy is rare, it is not a complete impossibility. It is found in some fishes, insects, and amphibians. The Argentinian rat is a good example and the only mammal to have been discovered very recently to undergo the rare process. It was found to have liver cells that are larger than the cells found in other relatives in the diploid family (Frawley & Orr-Weaver, 2015). From the observation, liver cells are the ones that are mostly affected by the polyploidy process in animals, as has been seen in animals with polyploidy.

As noted, the main disadvantage of this process is that it limits organisms from mating with their species because once they undergo polyploidy, they can no longer mate with the species members of the previous offspring. The dreaded reproductive isolation is created, which means that the new species has to look for a member of their new species.

 

References

Eweleit, L., Reinhold, K., & Sauer, J. (2015). Speciation Progress: A Case Study on the Bushcricket Poecilimon veluchianus. Plos ONE10(10), 1-16. 

Frawley, L. E., & Orr-Weaver, T. L. (2015). Polyploidy. Current Biology: CB25(9), R353-R358.

Gras, R., Golestani, A., Hendry, A. P., & Cristescu, M. E. (2015). Speciation without Pre-Defined Fitness Functions. Plos ONE10(9), 1-21.

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