Researchers Find Snakes Warm Up to Female Mimicry
Cross-dressing is surprisingly common in the animal world. Males of several species mimic either the appearance, behavior, or smell of females, thereby obtaining secretive matings or avoiding the aggression of larger rivals. However, researchers working with garter snakes in Manitoba have found that males produce a female-like scent (pheromone) not for any sexual advantage, but merely to warm up faster after emerging from hibernation.
In a recent Nature article, researchers show that the advantage of mimicry lies in becoming the object of 'mating balls,' large aggregations of as many as 100 amorous males that transfer heat to the female mimic, or 'she-male.' These findings were based on the research of former Earthwatch scientist Bob Mason of Oregon State University and colleagues from OSU and University of Sydney, building on the demographic work of Earthwatch teams.
"When you hear about female mimicry it is almost always in a sexual context or in a territoriality situation," said Mason, principal investigator of Earthwatch's Sex and the Single Snake and Great Balls of Snakes in the 1990s. "Here garter snakes are right in the breeding season and in a highly competitive breeding situation, and yet there is a much simpler explanation for female mimicry based on mere survival."
Mason and his colleagues discovered that she-maleness is only a transitory phase for the first day or two after a male emerges from hibernation, and could identify no mating advantage for the trait. Their alternative explanation stems from the fact that males emerging from hibernation are weak and slow, due to their cold internal temperature and lack of energy resources, and highly vulnerable to attack by crows and other predators.
"When these guys come out of the ground from hibernation, they're really cold, wet, and groggy," said Mason. "You can imagine what it's like for you on a winter's day, getting out of bed in the morning. These snakes have been underground for eight months, at about the same temperature as your refrigerator."
Using a series of ingenious field experiments, Mason and his colleagues demonstrated how snakes that are courted accelerate their own recovery from hibernation.
By gluing miniature thermal data-loggers onto females in outdoor arenas, the researchers showed that females in the presence of courting males warmed up from 4ºC to 20ºC significantly faster than females without males. The benefit of heat transfer from amorous males was often more than 3ºC, which could mean the difference between life and death for an emerging snake, whether it is truly a female or a she-male.
To measure the effect of warming up on female emerging from hibernation, the researchers compared the response of courting males to she-males that had been kept at two temperatures, warm and cool. They found that 'warm' she-males regained their he-male status within 3 hours, while 'cool' she-males remained attractive to courting males for more than 5 hours. Apparently, the higher temperatures gained by courted she-males accelerate their recovery from hibernation.
More than being a peculiarity of garter snakes in Manitoba, these findings suggest that biologists should look beyond sneaky mating tactics to explain female mimicry in other species as well. The demonstration that female mimicry in snakes offers advantages in thermoregulation and predator defense indicates that there could be many simpler evolutionary reasons for this unusual phenomenon.
"Situations of female mimicry that we already know exist should be examined in a new light," said Mason. "I'm not saying the other interpretations are wrong, just that people need to consider the simplest explanation."
For more information: Benefits of female mimicry in snakes. R. Shine, B. Phillips, H Waye, M LeMaster, and R.T. Mason. Nature, November 15, 2001, Volume 414 No. 6861
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