Question

Let us imagine that we are studying a population of mice, which are predated upon cats. Every few years we capture some of these mice and breed from them and then keep the progeny mice in the lab under standard conditions until they die. Over the duration of our study, we notice that the population of cats has been increasing.

a. What do we expect to happen to the longevity of our mice in the lab under the mutation accumulation hypothesis? State a central assumption you are making.

b. Now explain it under the antagonistic pleiotropy (AP) hypothesis.

Answer 1

Ans a) The mice are generated predated over by the cat and hence it reduces the longevity of the mice whereas due to the availability of the predation, it becomes easy for the cat to increase their overall population. Under the lab conditions, when there are some changes brought to the mice it leads to mutation accumulation and due to the evolution, it is observed that the age of the organism initially at which it is able to reproduce is changed and hence causes certain adverse effects. The longevity of the mice decreases due to the accumulation of the mutations.

Ansb) Antagonistic pleiotropy is when one gene is responsible for controlling more than one trait and one of these traits is beneficial for the fitness of the organism whereas the other is detrimental to well being of the organism. In terms of this hypothesis, with the accumulation of mutants the gene changes its pattern and hence the gene tends to be of characteristics where it tends to cause both beneficial and detrimental impact on the mice.

Answer 2

a. Under the mutation accumulation hypothesis, we expect the longevity of the mice to decrease over time. The central assumption is that harmful mutations will accumulate in the population due to a lack of selection pressure in the lab environment.

b. On the other hand, under the antagonistic pleiotropy hypothesis, we expect the longevity of the mice to initially increase due to selection for genes that confer increased reproduction and growth, which often coincide with increased longevity. However, as the population ages and the effects of genes with antagonistic pleiotropic effects become more pronounced, we may see a decline in longevity. This is because genes that confer benefits early in life may also have negative effects later in life. For example, genes that promote growth and reproduction may also promote cancer or other age-related diseases.