Question

Once you land on Kepler-452b, your new home, you observe many species of flora and fauna. The dedicated biologist that you are, you make note of the different types of species. You come across a bird-like species, and intriguingly you find that the members are either white or black, but very few exist in the shades in between. These birds are prey to a giant avian species, similar to hawks, and they spend most of their time hiding on the trees on the planet. The trees are nothing like the ones on earth; they have extremely white barks starkly contrasted with black leaves. From an evolutionary perspective, explain why the birds are mostly black and white, and the type of selection that led to this. Identify and explain an example of this type of selection on Earth. (Use words such as: disruptive selection, evolutionary pressure, natural selection, relative fitness)

Answer 1

Let's first look at the information given to us:

• The planet has birds with mostly of black or white colour. The grey( intermediate shade) has very few numbers.
• The birds hide on tree which has: BLACK LEAVES and WHITE TRUNK.
• These birds are prey to a giant avian species, similar to hawks, and they spend most of their time hiding on the trees

Now looking on all these facts it is clear that the number of black and white is high because these two colour birds have a place to hide on the trees. At the same thim the grey birds didn't have a place to hide and were not able to camouflage in the black and white environment. This increased evolutionary pressure lead to increase in their becoming prey to the giant avian species Vs other two colours. Hence this whole resulted in natural selection of black and white birds over intermediate birds due to their advantage.

This is known as DISRUPTIVE NATIRAL SELECTION, where the genetic variance selects extreme phenotypes. Here the average/ intermediate phenotypes are less for and are unlikely to feature prominently in the population.

On earth this similar selection is seen in case of beaks selection in Finches on Santa Cruz Island. Here disruptive selection was seen causing speciation in the population of finches. Due to forces of disruptive selection, intermediate beak sizes have been selected against for generations.

Hope this helps. Please let me know if you have any query.

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