Final answer:
Male little brown bats produce a lot of sperm because male fitness is primarily limited by the number of eggs they can fertilize. Sperm-depleted males maximize reproductive success by selecting fecund females when sperm is limited. This behavior, studied in behavioral biology, is influenced by natural selection to ensure efficient use of reproductive resources. Option number 1 is correct.
Step-by-step explanation:
The question asks why male little brown bats produce a lot of sperm. The statement that helps explain this behavior is: Male fitness is limited mostly by the number of eggs they can fertilize. This is because male reproductive success tends to be limited by the ability to mate with multiple females and fertilize their eggs, as opposed to the care of offspring or availability of females, which are generally more limiting factors for female reproductive success. Studies in behavioral biology, such as those on fruit flies, have shown that male fruit flies that had previously mated (sperm-depleted) picked larger, more fecund females more often than non-sperm-depleted males. This behavior maximizes the chances of reproductive success when sperm supplies are limited, ensuring that the sperm that is available is used to fertilize eggs of females that will produce the most offspring.
Additionally, in the context of natural selection, energy expended on mating practices such as producing colorful plumage or engaging in courtship rituals may reduce an animal's lifespan, but since reproduction has likely already occurred, this has less evolutionary disadvantage. In scenarios where sperm supply is low, males may alter their behavior to prioritize mating with females that offer a higher likelihood of reproductive success, thereby conserving their limited resources and maximizing their evolutionary fitness.