Final answer:
The conclusion after controlling for relatedness among bat species is that testes size in bats is related to the size of their social groups rather than their body size. The correct option is d) testes size is related to social group size
Step-by-step explanation:
After controlling for the effect of relatedness among species of bats, the conclusion with regard to testes size in bats is that testes size is related to social group size. This conclusion emphasizes that the size of a bat's testes doesn't have a direct correlation to its body size but is instead more closely associated with the social structures in which the bats live.
Larger social groups can mean more competition among males for mating opportunities, which can drive the evolution of larger testes to produce more sperm and, consequently, have a better chance of reproductive success.
Species with smaller group sizes or solitary lifestyles might have less competition, which could account for smaller testes sizes. This finding serves as a reminder of how animal behavior and physical characteristics are often a reflection of the social and environmental pressures that a species faces in its ecological niche. The correct option is d) testes size is related to social group size