Snakes usually learn about a prospective mate's sex and reproductive condition by large fat molecules that they sense through direct contact with their tongue. But new research from the University of Sydney suggests their sexual selection may also be influenced by an ability to 'smell' airborne pheromones.
Credit: Veer
PhD student, Mike Wall researching garter snakes. The researchers' experiment involved placing a female snake inside an empty margarine container, and pushing the pheromones (via concentrated air) through air holes to males on the outside.
Credit: Tracy Langkilde
ABERYSTWYTH: Snake sex may be more complicated than we thought, as new research suggests snakes select a suitable mate by smelling airborne molecules released during copulation.
By studying snake sex pheromones, researchers at the University of Sydney have found that snakes are not only able to sense molecular communications through direct contact of their tongue, but are also able to 'smell' airborne molecules.
"Snakes usually depend on large fat molecules to tell them about another snake's sex and reproductive condition. Because these molecules are large, they don't float through the air - and so, a snake picks them up by tongue-flicking the body of another snake directly, or by tongue-flicking a trail that the other snake has left on the ground," said lead author Richard Shine, of the paper published in Biology Letters today.
"Our work shows that snakes are more flexible that we had realised - they are quite capable of using airborne cues as well, involving different kinds of molecules, so long as these provide useful information."
Smelling pheromones
Like many other animals, snakes rely on chemicals (pheromones) to work out the sex and mating status of potential partners. Most snake pheromones are lipids (fats) that are assessed by direct contact, such as when a male tongue-flicks a female's skin, or the ground where she has travelled.
The new research shows that males can detect that a female is mating - and so will stop trying to court her - from the airborne scent of the fluids produced during copulation. Using very simple methods, the researchers looked at the mating process in garter snakes, exposing courting male snakes to smells released by female snakes, male snakes and two mating snakes, and noted any changes in behaviour.
"We took an empty margarine container, and cut two holes (one on each side) through which we could pass hollow flexible plastic tubes. One tube ran to a portable aquarium pump, so that when we switched on the pump it pushed air through the margarine tub and out the tube on the other side," said Shine.
"We placed our 'stimulus' (say, a female snake) inside the margarine tub, and held the outlet opening close to the heads of courting male snakes at the den. That way, we could expose them to specific smells, but without giving them access to the large surface-bound molecules that snakes generally use as sex pheromones."
As predicted, when courting snakes were exposed to smells issued by the mating pair of snakes in the margarine container, the courting stopped.
A strategy for reproduction
The research suggests that snakes are able to adjust their behaviour to take advantage of certain cues in their environment to maximise their chances of reproductive success.
"Previous studies by these authors have shown that the presence of sperm plugs plays a significant role in the prevention of re-mating by females. The pheromonal evidence described here shows that sperm plugs are not the only deterrent employed by males to maximise their reproductive success," commented Warren Booth from North Carolina State University in the U.S., who was not involved with the study.
"Thus, we have evidence that males have evolved multiple strategies, both physical and chemical, to prevent females re-mating, and therefore to maximise their reproductive success," Booth added.
"In many species, courtship is an energetically expensive behaviour that can reduce or even eliminate a male's reproductive success if he is unable to find a responsive female. In instances where visual confirmation is not available olfactory cues in the form of airborne sex pheromones, as described here, provide the only information available to a male."
