Bat balls

In my evolution class we are studying adaptations. For the record, an adaptation is any trait that enables an organism to get its genes into the next generation better than the next guy. As I tell my kids, " Reproduction is the name of the Evolutionary Game."
So some people went into cave that had large bat populations and measured the size of the males' testes. Yes, you read that right. And by now you're wondering how bat ball size leads to an evolutionary advantage. Turns out, female bats are whores and will sleep with many men... batmen... male bats...whatever. And as you all know, when it comes to sperm and fertilization There Can Be Only One. The Bat Ball Theory goes something like this: Since the female mates with several males during her estrous cycle (we rednecks call that "in heat"), the male must make sure his sperm is The One. He does this by making the most ejaculate! Hence the big balls. And, interestingly enough, the bigger the size of the roosting population of bats, the bigger the average bat ball size.
 Can't you just see it- Bat sperm everywhere! Ewww, don't think I want to see it.
But....there's a tradeoff. Turns out, it takes a lot of energy for a bat to make all this ejaculate. Since his energy budget is finite, he must give up something. In this case, big bat balls means small bat brains. Yes, the males are happy to give up their brains to have big balls. Maybe the balls are a substitute for the brain?

Just think, someone got money from the federal government to study this, and then paid themselves....
You gotta love our country.