There is a population of squirrels that existed together at one point in time. O

Question

There is a population of squirrels that existed together at one point in time. Over the last million years, a mountain divide has separated half the individuals on the north side and the other half of individuals on the south side. Another million years pass, and the mountain crumbles allowing individuals of both populations to meet. If the two populations have evolved into “new” species, explain at least 5 isolating mechanisms that would prevent them from mating and producing viable offspring. There are five prezygotic isolating mechanisms and there are three postzygotic isolating mechanism.

Explanation / Answer

Prezygotic Isolating mechanisms:

1. Mechanical Isolation: it is the incompatibility of the sex organs. In this type of isolation mechanism, the species develop sex organs which are incompatible with the other species and prohibits them from mating.

2. Behavioral Isolation:It may so happen that the two evolved species are in close proximity but have evolved different mating behaviours that keeps them away from mating.

3. Zygotic isolation: for fertilisation to happen the female egg should fuse with the male sperm and form the zygote. For this the egg and sperm should have chemical compatibility. But having evolved to different species, the two species may not have lack the compatibility between the egg and sperm which will prevent their mating.

4. Temporal Isolation: Having evolved differently, they might have developed different mating seasons. As a result of which the two desired species will not be fertile at the same time and may not mate.

Postzygotic Isolating mechanism

1. Non-viable zygote: In certain cases, the egg and sperm may fuse to form a zygote, but due to difference in the genetic makeup of the two species, the zygote will not have the desired genetic and cellular makeup. In this situation, either the parent self aborts the zygote or even if it is given birth, natural selection will prefer only the best fit organisms and eliminate the rest.

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