The Cold Blooded News The Newsletter of the Colorado Herpetological Society Volume 28, Number 10;   October, 2001

Researchers Throw a Curve into Snakes' Mating Game
(Blue racer Coluber constrictor foxi)

By Jenni Laidman, Toledo Blade Science Writer, May 28, 2001

I'm not a quick study. Once, in college, I was sitting in biology lab when war seemed to break out in the mouse house. The inhabitants were running and squealing and wrestling, and in my highest moment of college girl dumb, I blurted, "Oh no, they're fighting!"

"If you think that's fighting, you can skip the final because you just flunked," the professor said.

So, it shouldn't surprise you that it took me a moment to figure out what the pair of blue racers were doing in the road at the Kitty Todd Nature Preserve in the heart of the Oak Openings region last spring.

But they were doing it, and I watched. Without ceremony, the snakes finished their business, and each slithered off on its own, blue streaks disappearing into the grass in an instant.

It didn't occur to me until much later that the snakes were doing something amazing. After all, snakes have done it forever, or there wouldn't be all these little snakes growing into bigger snakes each August. So it seemed perfectly natural.

Then I picked up an issue of the scientific journal Behaviour. I will never look at snake-mating the same way again, thanks to the work of Rick Shine, an Australian evolutionary biologist; Dave O'Connor, also of the University of Sydney, and Robert T. Mason of Oregon State University.

The article that caught my eye? "The Problem with Courting a Cylindrical Object: How Does an Amorous Male Snake Determine Which End is Which?"

Now is the time of year when blue racers are busy figuring this out, says Val Hornyak, a reptile keeper at the Toledo Zoo. By the end of summer, the dunes in the Oak Openings will be peppered with the remains of the racers' weird emery board-textured eggshells, annual proof that they manage it somehow.

A team of researchers decided to figure out just how snakes make this determination. But these researchers looked at a species that has bigger problems than the mere lack of recognizable feminine topography.

The species they study is the red-sided garter snake. These animals are famous for their annual spring mating frenzy in Manitoba. The snakes form "mating balls," where countless males wrapped around a beleaguered female. Apparently garter snakes aren't good at forming lines. This is how they wait their turn.

Although blue racers avoid such mob scenes, the issues of copulation navigation are the same from snake species to snake species. In order to find out what map the males follow, the researchers found ways to test their best ideas, and in the process, confused the poor snakes during an activity they normally accomplish without difficulty.

At first it appeared as though the best cue for mating males to follow might be the direction of female travel.

Researchers tied a string to a dead female. When they pulled the female head first, all males lined up properly with her. But when they pulled the female tail first, males managed to face the right way in only 14 out of 25 tests. Direction of travel, it appears, was far from a perfect cue.

So researchers took the dead female and just stretched her out on the ground. The discriminating males approached her, and often began courting from the wrong direction.

Since the female wasn't available to make sarcastic remarks, the males kept to their task. After initial awkward flirtations, the males all managed to get themselves headed the right way. Obviously something was tipping them off with a far more powerful signal than the female's direction of travel.

To make sure the location of the female's head wasn't the signal, researchers cut it off. Still the males eventually found their way.

Maybe the tail was the signal. Researchers cut that off too. The desperate males still figured out which end was which (although at this point, it seems an empty skill. Like golf.)

It gets weirder.

Researchers wondered if the cue was in the skin. So they cut the skin off the headless, tailless female and wrapped it around a metal pole. As long as the skin was "fresh" males got it right 10 of 11 times. When they tried the test again with an old skin, only seven of the 21 attempts were from the proper direction.

By this point, it was clear that the direction signs were chemical.

So researchers sprayed live females with plastic skin. It changed nothing. Males still courted, and properly. Then researchers washed the females in a substance that removed sex pheromones. Although this eroded their popularity considerably -- washed females had 7.1 courtships compared with the 25.9 courtships for unwashed females, the few suitors who approached did figure out which way to face.

Comparing the signs the males seemed to use for navigation with the signs they couldn't use consistently or at all, the researchers came up with a theory.

In snake-mating, males press their suit by pressing their chin along the female's body. At the same time, they flick their tongue, which is covered with important chemical sensors. Other studies have found that males rub their chin against the grain of the female's scales more often than in the same direction as the scales.

The authors theorize that feminine pheromone concentrations are heaviest at the hinge of each scale. By pressing the scales against the grain, the male is essential squeezing the atomizer of female pheromone. These pheromones are apparently too deeply embedded in the skin to be washed off or damaged by plastic coating. In fact, other studies show the only way to stop the male's mating efforts is to block his sensory system.

Since male blue racers also court with chin presses, it's likely this is the clue they use as well to find the right direction to mate.

Maybe they face the other way for fighting. I'm never quite sure.

| Next Article: For the Love of Frogs |
| Previous Article: Natural History of the Central Asian Tortoise |
| Return to Cold Blooded News Page | Return to CHS Home Page |