You decide to study two species of birds, both of which form monogamous pairs (one male and one female). In species 1, you find that the eggs in a pair's nest are in fact almost always the offspring of that pair. In species 2, you are surprised to find that many of the eggs in a nest were actually fathered by males of neighboring pairs. Apparently, mating outside of monogamous pairings is widespread in species 2. Given this information, what would be the logical prediction to make before comparing testes size of males of the two species?
A) Testes of species 1 are larger than testes of species 2.
B) Testes of species 2 are larger than testes of species 1.
C) There is no relationship between this observation and the size of the testes.
D) The testes of the individual within each species would be exactly the same size.

Question

Quizplus · Accepted Answer

In species 2, where mating outside of monogamous pairings is widespread, the males would have evolved larger testes to produce more sperm and increase their chances of fathering offspring. In species 1, where offspring are almost always the result of the monogamous pair, the males would not have to compete as much, and therefore would not need to evolve larger testes.

You Decide to Study Two Species of Birds, Both of Which