Q1: Summarize key differences between allopatric and sympatric speciation.
As we know, the term speciation refers to the process of emergence of new specie on earth due to increase in the genetic diversity of the gene pool of an organism. Allopatric and sympatric are basically mechanisms through which speciation occurs in the world and below are the major differences between these two:
- In Allopatric speciation, there is a physical barrier between two populations due to which no genetic exchange or gene flow can occur between two population to lead the formation of two new specie over the course of time, on the other hand, in sympatric speciation, two species live in the same geographical area and there is no physical barrier between them, but due to certain traits like preference of certain shelter or food or zygotic incompatibility they donot mate much and eventually develop into new separate species.
- Allopatric speciation is basically nature driven and operates through natural selection, while sympatric is driven through the mechanism of polyploidy when chromosome set is replicated.
- Allopatric speciation is common in both plants and animals, while
sympatric is common in plants.
- In Allopatric speciation the rate of emergence of new specie is slow fast but in sympatric speciation it is relatively faster.
- The example of allopatric speciation is the formation of new species of Darwin's finches in Galapagos Island, while the example of sympatric speciation is Alloploid species of Wheat.
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Q2: Which type of speciation is more common and why?
Allopatric speciation is more common in nature as compared to Sympatric because the main factor leading to speciation in Allopatry is geographical barriers while in the latter one they are nature induced gene flow in population living in same area. Hence geographical barriers are more powerful factor that greatly lessens the transfer of genes in a population while in Sympatry the reduction in genetic flow is less because after all population is living in same habitat.
Here we can take an example of Galapagos Island finches, which were a same specie of finches but when they were isolated through geographical barrier, there were remarkable difference created in the novel species of finches as compared to parent specie. On the other, If we think about the novel varieties of Wheat plants that arise through polyploidy, this polyploidy is only restricted to plants and donot occurs in animals and therefore it is less common.
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Q # 3: Describe two mechanisms that can decrease gene flow in sympatric populations, thereby making sympatric speciation more likely to occur
The two possible mechanisms that can reduce genetic flow in symatric populations are:
1: Changes in chromosome: As we just discussed the example of polyploidy in wheat in which chromosome set is duplicated and new species are formed, in this way they are not able to breed with original parental population and this makes process of Sympatric speciation more likely to occur.
2: Habitat differentiation and sexual selection: This is the second major cause that can lead to Sympatric speciation, What happens in it that some members of a population (the cause is not known) have better preference for a certain place or habitat rather than other and some due to zygotic incompatibility cannot produce offspring due to which they are slightly isolated and with the passage of time give rise to separate specie and ultimately favors sympatric speciation mechanism.
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Q 4: Is allopatric speciation more likely to occur on an island close to a mainland or on a more isolated island of the same size? Explain your prediction.
Allopatric Speciation is less likely to occur in an Island close to a mainland and more likely to occur on an Isolated Island, The reason again lies in the definition of Symaptric speciation. When the Island is in close proximity of mainland, obviously there will be a continuous genetic flow between mainland and Island because of their less distance and less chances of genetic divergence. On the other hand if they are suitably separated through a substantial distance, there will be more chances that some members of specie will acclimatize new area better and with the passage of time, will evolve into new species.
Hope it helps!