Select as many responses as are correct. Under the evolutionary theory of senesc

Question

Select as many responses as are correct. Under the evolutionary theory of senescence, populations with lower ecological mortality should evolve delayed senescence because:

A. late-acting deleterious mutations would be under selection in more individuals and are more likely to be at lower frequency in mutation-selection balance

B. antagonistically pleiotropic mutations would be less favored by selection because longer-lived individuals will experience more of the later-life costs

C. Population sizes will be larger

D. Older individuals will bear fewer offspring later in life

Explanation / Answer

Choices A, C and D are correct.

Reason: The modern theory of senescence and evolution states that late-acting mutations play role in evolution of species with low mortality rates. This is because when late-acting mutations take place in individuals of a population, these organisms spend a major part of their life-cycle in initial phases rather than later phases. This helps the genes associated with senescene to be expressed late and thus evolve with delayed senescence. This indeed promotes an increase in population size because the organisms spend a major time of their life cycle in reproductive phase and hence, more offsprings are produced. This is further validated by the fact the reproductive efficiency is decreased with increase in age and older individuals bear less number of offsprings.

Importantly, the antagonistically pleiotropic mutations also play a crucial role in this phenomenon since the genes which initially help in survival and increase fitness of an organism revertently play a detrimental role in senescence and death. Thus, choice B is incorrect.

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