Question

10a). Compare and contrast allopatric and sympatric modes of speciation.

10b). Compare and contrast prezygotic and postzygotic reproductive isolating mechanisms.

10c). The biological species concept is based on the assumption that species are reproductively isolated and do not share genes. And yet a number of organisms that are considered different species hybridize (mate and exchange genes). Hybridization between different species is more common in plants than in animals. Propose some possible reasons for this difference.

Answer 1

10.a. Answer: The difference between the allopatric and sympatric modes of speciation:

Allopatric speciation means which occurs between two population or same species are living in separate environments and there is no gene flow between the populations. It is also called as geographic speciation. Example: Grand Canyon was formed; it was a natural barrier between the squirrels living in the particular area.

Sympatric speciation means which occurs between two population or same species are living in same environments. This speciation undergoes pre-zygote or post zygote that prevent gene flow, but species occupy same related species which is compatible. Example: The ancestors of hawthorn usually lay their eggs on hawthorns but now-a-days lay their eggs on both apples and hawthorns.

10.b. Answer: The difference between the pre-zygotic and post- zygotic reproductive isolating mechanisms:

Reproduction isolation is a mechanism that keeps species for mating with others. Pre –zygotic isolations are the species which prevent species from interbreeding with each other. Example: prevents egg fertilization. The mechanisms include in this are seasons mating, habitat isolation, mechanical isolation, gamete isolation and behavioral isolation.

Post-zygotic isolation that ensure the hybrid offspring are not selected for by natural selection (i.e., hybrids are produced but tend not be viable). Example: prevents formation of fertile off spring.The mechanisms include in this are hybrid break down, hybrid sterility, hybrid inviability.

10.c. Answer: The possible reason for the differnce is as follows:

Hybridization between different species leads to formation of new species, reproductively isolated from the parent species. This mostly seen in plants than animals because plants are more tolerated with polyploidy.

For example: Saxifraga are more tolerated with polyploidy and are hybrids ( produce tetraploid natural hybrid - Saxifraga osloenis) which is formed at the end of the ice age. Wheat plants are also more tolerated with polyploidy. In palnts also it causes more efficiently homoploid hybrid species example: sunflower.

Homoploid speciation is seen in animals and only few animal species involve hybridization that too with plants only. For example: Heliconius butterflies causes homoploid hybrid speciaton, It produces new color pattern which is seen in putative parent species. The putative hybrid is genetically more similar to one of its parents. The reason of the new color is due to the direct influence on the reproductive isolation between the hybrid and both parents.

Note: The provided answer is as per my knowledge may be or may not be 100% correct, but definitely relevant to your question thank you so much.