Question

A population of small, insect-eating mammals stumbles across a cave and finds that it provides shelter from the weather, protection from predators, a source of clean water and, surprisingly, a seemingly endless supply of insects. Because maintaining complex organs, like eyes, can be costly, the population begins to adapt to life in the cave by reducing its investment in vision. Adaptations to vision for this cave-dwelling population most likely includes:

A. a decrease in the size (or magnitude) of each action potential sent to the brain via the optic nerve.

B. an increase in the number of mechanoreceptors that generate action potential in the eye.

C. an increase in the ratio of rods to cones in the retina of the eye.

D. a decrease in the size of the eye’s pupil.

Answer 1

C. An increase in the ratio of rods to cones in the retina of the eye.

Rods are for night vision and cones are for bright vision. Caves are dark most of the time due to which cones are of little importance. But vertebrate eye has both rods and cones. Even though rods and cones are not functioning due to lack of light, their resting membrane potential needs to be maintained even in the absence of light. Maintaining rods is cheaper compared to maintaining cones, that is why as adaptation rods are more in such cave dwelling animals than the cones.