Male bats with developed brains tend to have relatively “modest” testes. Researchers explain that this correlation arises because both organs require a significant amount of energy to develop, forcing species to find an optimal balance.
An analysis of 334 bats revealed that in species where females are promiscuous, males possess larger testicles but comparatively smaller brains. Conversely, in species where females are loyal, the situation is reversed. The fidelity of males does not affect the size of either their brains or their testes.
Both brain tissue and sperm cells require substantial metabolic energy for development and maintenance. Different species prioritize the development of one organ over another, all aimed at increasing their reproductive success.
“The testis mass of bats ranges from 0.12% to 8.4% of body mass, surpassing that of any mammal. In primates, testis mass accounts for only 0.02-0.75% of body weight,” said Scott Pitnick from Syracuse University, USA.
Efficient energy use is crucial for bats, Pitnick noted: “They are small creatures flying over vast areas, and they need to fly extensively, especially during the breeding season.”
Initially, Pitnick and his colleagues hypothesized that in species with promiscuous females, males would require larger brains to avoid being “cuckolded.” Thus, they were surprised to find the opposite. “Perhaps fidelity actually requires more neurons.”
Harry Moore, a researcher at the University of Sheffield, UK, stated that testis size is often related to sperm quantity. “In species with promiscuous females, males must compete to fertilize their eggs and therefore need to produce more sperm. This is especially true in bats, where females can store sperm for several months.”
M.T. (Newscientist)