Friday, March 16, 2012

Orgy at the Pool

An idyllic puddle in the woods, you may be thinking, just the perfect spot for a few minutes of meditation on an balmy spring evening. Think again.

This is actually a vernal pool, a polite term for a den of orgy. The shallow water roils with hormonally-charged frogs, croaking loudly enough to be heard a quarter-mile away. Perhaps not the most conducive spot for an evening of peaceful philosophizing, but a fascinating place nonetheless that deserves a visit.

The participants in this orgy are Wood Frogs, Lithobates sylvaticus. As their name implies, these small frogs are denizens of woodlands. Indeed, they have abandoned the water except for reproduction, which is explosive; after the first warm days of the spring, the entire population descends upon traditional breeding pools, and, after a few frantic days of calling, fighting, mating, and laying eggs, returns to dry ground for the remainder of the year.

A pool filled with several hundred calling male Wood Frogs is a scene not quickly forgotten. Their guttural croaking is reminiscent of a quacking duck. To get an idea of the experience, watch this video.

The males float around on the water, croaking and fighting among themselves. Paired sacs on the sides of their necks inflate as they call, and often they lunge through the water in pursuit of other frogs as they call.

Mating is a process of trial and error. The males grab every frog they can until they find a female. If another male is grasped, the assaulted male will squeal a "release" call to inform the other male of his mistake. As you can imagine, the pond water roils with the chaos.

Eventually, however, things work out and a male and female will mate. And, since I'm sure that you're as fascinated by frog sex as I am, I can't help but dive into the gory details. Almost everyone has seen frogs or toads mating in ponds, the male clinging for dear life to the back of the female. But did you know that frog fertilization is actually external? That's right--frog mating is a form of pseudocopulation known as amplexus. The male wraps his front legs around the female's body, assisted with special nuptial pads on his thumbs. As she lays the eggs, he squirts out the sperm, and so the next generation of frogs is conceived.

Wood Frogs are fascinating creatures. They are the most widely distributed frog in North America, ranging north of the Arctic circle. Such a northerly distribution requires extraordinary adaptations, and the Wood Frog's method of surviving the winter is truly fabulous: it freezes. It produces antifreeze, composed of glucose, which supports its cells while the water crystallizes. The brain is inactive; the heart stops beating.

Birds seem so boring in comparison!