A researcher discovered a species of moth that lays its eggs on oak trees. Eggs are laid at two distinct times of the year: early in spring when the oak trees are flowering and in midsummer when flowering is past. Caterpillars from eggs that hatch in spring feed on oak flowers and look like oak flowers, but caterpillars that hatch in summer feed on oak leaves and look like oak twigs.

Question

How does the same population of moths produce such different-looking caterpillars on the same trees? To answer this question, the biologist caught many female moths from the same population and collected their eggs. He put at least one egg from each female into eight identical cups. The eggs hatched, and at least two larvae from each female were maintained in one of the four temperature and light conditions listed below.

Temperature Day Length
Springlike Springlike
Springlike Summerlike
Summerlike springlike
Summerlike summerlike

In each of the four environments, one of the caterpillars was fed oak flowers, the other oak leaves. Thus, there were a total of eight treatment groups (4 environments × 2 diets).

Recall that in the experiment, caterpillars born in the spring looked like flowers, and caterpillars born in the summer looked like twigs. What is the most likely selective advantage for this difference in body shape?

A. Looking like their food sources allows the caterpillars to move through their environment more efficiently.
B. Development into the adult moth form is faster for caterpillars shaped like twigs than like flowers.
C. Looking like their food source will increase the caterpillars' feeding efficiency; this would increase their growth rate and survival rate.
D. Looking like their food source lets the caterpillars blend into their surroundings, reducing predation.

Answer 1

The most likely selective advantage for the difference in body shape between the caterpillars is:

D. Looking like their food source lets the caterpillars blend into their surroundings, reducing predation.

This camouflage allows the caterpillars that resemble flowers to avoid predators when feeding on oak flowers in the spring, and the caterpillars that resemble twigs to avoid predation while feeding on oak leaves in the summer. By blending into their environment, they are less likely to be seen and eaten, thus increasing their chances of survival.