In the figure below, the lighter gray circles represent single-male breeding systems in primates and the darker gray circles indicate multi-male systems. Which of the following statements is consistent with these data?
A) Single-male breeding systems select for smaller testes size because sperm are not needed to increase reproductive success.
B) Body weight does not influence testes size because selection only favors large testes in multi-male systems.
C) Species with multi-male systems evolve larger testes because they have higher body weights.
D) Selection favors large testes relative to body weight when a male's sperm must compete directly with other males.

Question

In the figure below, the lighter gray circles represent single-male breeding systems in primates and the darker gray circles indicate multi-male systems. Which of the following statements is consistent with these data? 
A) Single-male breeding systems select for smaller testes size because sperm are not needed to increase reproductive success. 
B) Body weight does not influence testes size because selection only favors large testes in multi-male systems. 
C) Species with multi-male systems evolve larger testes because they have higher body weights. 
D) Selection favors large testes relative to body weight when a male's sperm must compete directly with other males.

Quizplus · Accepted Answer

The data shows that species with multi-male breeding systems have larger testes size than those with single-male systems. This suggests that selection favors larger testes when a male's sperm must compete directly with other males. This is consistent with the explanation for the evolution of large testes in species with multi-male systems, where greater sperm competition requires males to produce more and/or better quality sperm to increase their reproductive success. The data does not support the other options, as there is no clear relationship between body weight and testes size, and single-male systems do not necessarily select for smaller testes.

In the Figure Below, the Lighter Gray Circles Represent Single-Male