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Snake Camouflage Deters Predators.

Harmless snakes using the colors of dangerous species to protect themselves from predators can successfully get away with this strategy--but only in areas where deadly snakes are found, according to researchers at The University of Texas at Austin and the University of North Carolina at Chapel Hill. Their studies add new weight to the evidence for natural selection.

The researchers focused on predator behavior toward extremely poisonous coral snakes, noted for their ringed markings of red, black, and yellow, or red, black, and white, along with their harmless imitators, the kingsnakes. The theory of Batesian mimicry holds that edible species that look like dangerous species will be protected, because predators evolve to avoid dangerous species--even without previous, real-life, bad dining experiences.

"Mimicry has been used as the preeminent example of how natural selection works and why it works the way it does," indicates Karin Pfennig of the University of Texas' College of Natural Sciences. "There is very strong selection for predators to avoid snakes with these kinds of ringed patterns because they look dangerous. This is probably not based on predators having previous experience with coral snakes, because all it takes is one bite and you're dead. You're out of the gene pool."

The researchers predicted that the protective effect of looking like a coral snake would break down in those areas where poisonous coral snakes were absent. Under such circumstances, the process of natural selection would not operate to eliminate heedless predators. There would be no need for color-conscious predators to evolve.

To measure predator attacks, the researchers and their assistants constructed about 1,200 fake snakes composed of nontoxic plasticine threaded onto an S-shaped wire. They used caulk guns to squirt out appropriately sized tricolor, striped, and plain brown snakes. The striped and brown snake replicas were intended as controls.

The number of attacks by carnivores was measured in 40 different locations, including 14 sites in Arizona where coral snakes were known to occur and 10 sites where they were known to be absent. Half of the 16 Carolina sites were home to real coral snakes and half were not.

"When a predator attacks one of these plasticine replicas, it leaves tooth marks. It's a permanent record," explains Pfennig. "Animals have distinctive tooth patterns, so we were able to come along several weeks later and say what kind of predator it was." The group primarily focused on the behavior of snake-eating mammalian predators, such as foxes, coyotes, raccoons, and even black bears. "We probably didn't get a lot of hawk predation because we tended to put the replicas in more forested areas," Pfennig points out. Bear attacks were rare, but they did occur both in Arizona and the Carolinas because "bears will eat just about anything."

The researchers found that, as predicted, the number of attacks on the ringed replicas gradually rose with higher altitude or more northerly location. The attacks increased in areas with few or no coral snakes because predators had not evolved to recognize the patterns. Pfennig notes that, "As you move further north or move higher in altitude, coral snakes become increasingly rare--and attacks on the ringed snakes gradually increase. It's exciting to find this pattern of natural selection working and to be able to measure the gradual change as elevation or latitude changes."
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Publication:USA Today (Magazine)
Article Type:Brief Article
Geographic Code:1USA
Date:Jun 1, 2001
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