Bats on the Brain

This past weekend, while up at Crystal Mountain, we stayed at a friend's cabin about 20 minutes north of the mountain. It is a quaint, rustic setting: no TV, summer-camp style bunk-beds, ever-cozy thanks to a big wooden fireplace and stove. And bats. Well, one bat, to be precise. Our friendly echolocator only made a couple flitting appearances, and we made no efforts to run him out. Given the number of mice we end up removing each time we arrive, this bat has probably got it good in the cabin when we're not around.

We got to thinking more about bats this week as we returned to the working world. We're used to desert bats from Utah--are they remarkably different here? How big do they get round these parts? A quick call to Bats Northwest, whose website promised to answer these and even more "urgent bat questions" yielded solely voice mail, and no respite for our bat inquisition. Little did we know, perhaps we should have been more concerned with how big their parts get.

Seattlest wakes up this morning to hear the chirrupy morning radio people discussing bats...and their balls. A recent scientific study is making the news feed rounds, as researchers discovered that in bats, males make an evolutionary trade-off between brain size and cojones. Growing any of those suckers is apparently one of the more biologically demanding developmental feats for bats. Since bats' metabolic needs go up to 11, given that they have extremely high energy requirements to stay in flight, over time they've adaptively let two win over the other one.

The results from the study generating the most buzz are: monagamous bats have larger brains (relative to their overall body size) than their counterparts that get around the bat cave a bit too much, and secondly that male bats with larger brains have smaller testes. Science blogger ScienceGrrrl offers more detail on the research and findings, quoting one of the primary researchers:

"In species with promiscuous females, the males are competing to fertilize her eggs and so need to produce a lot of sperm," Pitnick said. "And this may be especially true in some species of bats where the females store sperm for several months."

"If female bats mate with more than one male, a sperm competition begins," Pitnick elaborated. "The male who ejaculates the greatest number of sperm wins the game, and hence many bats have evolved outrageously big testes."

She also noted that the largest testes found in bats were 8.4% of total body mass, and does the math for you: assuming that the average man weighs 160 pounds, he would have balls that weigh in at thirteen-and-a-half pounds.

And now, we leave you to an entire day with AC/DC in your head. You're welcome.