MN Press: Researchers flock to Interlake to study snake sex
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Posted by W von Papineäu on May 12, 2003 at 20:43:41:
WINNIPEG FREE PRESS (Manitoba) 02 May 03 Coiled courtin' Researchers flock to Interlake to study snake sex (Tina Portman)
A Manitoba red-sided garter snake pit in spring is an orgy of thousands of snakes -- and an opportunity for snake researchers to conduct more studies of snake reproduction, physiology, ecology and endocrinology than researchers of other snake species can do in a year. "Most of my colleagues will be lucky to see a dozen matings in their lifetimes," says Robert Mason, a physiological ecologist from Oregon State University who has studied Manitoba's red-garter snakes for more than 20 years. "Here we see that in 10 minutes."
Mason is standing in a bedroom-turned-office at Manitoba Conservation's Chatfield Research Station in the Interlake. Two graduate students are weighing and measuring garter snakes in margarine containers on the kitchen table. More snakes wait their turn in floral and plaid pillowcases piled on the floor. Mason is holding a jar containing a clear liquid. Snake Love Potion No. 9.
The jar actually contains a suite of molecules called methyl ketones -- garter snake sex pheromones -- dissolved in an organic solvent. Snake pheromones are physically similar to margarine fats and, like margarine fats, some methyl ketones are saturated and some are unsaturated. In 1989, Mason found that it's the unsaturated pheromones produced by females that work magic on males.
Mason says Manitoba's long, cold winters force snakes underground into caves, where groups of thousands or tens of thousands survive the season below the frost line. They emerge when the snow melts and the sun shines in spring, usually the end of April and beginning of May. Mason is usually waiting for them.
Spring garter snake behaviour is completely driven by pheromones. When females emerge dirty, cold and slow from the limestone underground, they are betrayed by the sexy pheromones assimilated into their skins.
"Females are underground for six months," says Mason's colleague, Richard Shine, a behavioural and evolutionary ecologist from the University of Sydney in Australia who is also lured to Manitoba each year by red-sided garter snakes. "Ten seconds after their heads are out, they have 100 boyfriends."
Because male garters emerge from hibernation en masse while females come out a few at a time, in early spring there can be 100 males for every female in the main Chatfield snake study pit, which is on top of the caves in which the garters hibernate. Females are larger than males, but it's a rare female that is strong enough to drag her entire entourage up the side of the snake pit. Most waste their energy gaining tens of centimetres, only to be dragged back by a rope of clinging suitors.
Females may be harassed, but the males are completely driven. They don't eat. They court. After losing 10 per cent of their body weight over a winter of hibernation, they emerge in spring and lose one per cent a day for about 30 days of mating.
A male garter snake courts anything that smells, to his flicking tongue, like a female -- a newly emerged male stinky with female pheromones (called a "she-male"), a dead female ("male snakes don't let a little thing like death stop them," says Shine), even a paper towel dipped in female pheromone. A paper towel is so obviously not a snake, and the crease in the paper towel that a male will attempt to breed is so obviously not a female's gaping cloaca, that the only explanation is a complete pheromonal override of all snake sense.
"We don't even have to make a (snake) model," says Mason. "The males try to mate with the paper towel -- males identify the paper towel as a female."
In their pheromone research, Mason and his colleagues not only identified the methyl ketones, they were able to synthesize them in a laboratory. The synthetic pheromones also attracted males to paper towels.
On a snake, the pheromones don't soak the skin like sweat; they are embedded in the skin in a layer of skin fats (lipids).
"We don't think of ourselves as greasy," says Mason. "But all critters on land, including insects and vertebrates, have a micro-molecular layer of skin lipids that retards water loss. It's not like we're covered with Crisco, although Crisco would work just as well."
When a female garter snake finally chooses to be bred by one of her male groupies, she gapes her cloaca, the opening that serves both reproductive and elimination functions. One male inserts one of his two hemipenes (according to Shine, usually the right one), his sperm and, after he's finished in 15 minutes or so, a gelatinous chastity plug that resembles a daub of silicone glue. During the coupling, the female has her only revenge on the pushy male when she drags him around by the hemipenis. (Mason has seen bloodied, hemipenis-less male garter snakes slithering around the pits. He thinks that a hemipenis can regenerate.)
Mating gives a female relief from harassment. After mating she becomes unattractive by producing an unsexy copulatory pheromone. Males leave her alone until the chastity plug breaks down and falls out, in 24 to 36 hours.
Male garter snake skin contains saturated methyl ketones as well as a compound called squalene. She-male garter snakes, a temporary phase in the life of male garter snakes, produce a combination of saturated and unsaturated methyl ketones, and no squalene. Although there's no actual mating, other males court she-males and wrap them up in mating balls.
Mason and Shine uncovered the secret behind she-males two years ago. Snakes are cold-blooded, which means that they can't produce their own body heat. They must absorb heat from the rocks, earth and sun. A cold snake is a slow-moving snake. Mason and Shine found that she-males are male snakes that have just emerged from the cool underground. They are cold and wet and can't move very quickly.
"A she-male is a crappy courter, and a crappy runner," says Mason. "(At the snake pits) crow and bird predation is high." So she-males suck heat out of other males that had emerged from hibernation earlier and they are covered up in mating bundles when the predators come.
"Manitoba is the Shangri-la of snake research," says Shine, who is studying physiological stress in courted female snakes. "For snake researchers, to see any snakes courting is exciting. Here it's all over. It's a real privilege to work on these little darlings."
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