Though the study was conducted in the Mediterranean region, Foufopoulos said he suspects the results apply to other parts of the world-such as the American Southwest or Australia-where lizards coexist with venomous snakes. "You lose your tail, but you come away with your life," Foufopoulos said. In that case, the ability to shed a tail within seconds-before venom reaches the lizard's vital organs-becomes a life-or-death matter. When non-venomous predators attack, tail-shedding is only useful in the relatively rare instances when the tail is firmly grasped by the predator.īut when a viper bares its fangs and strikes, even glancing contact with the lizard's tail can inject a lethal dose of venom. This result is perhaps best explained by the peculiarities of viper attacks, Foufopoulos said. But no one had made this connection, until now." "So it makes sense, in retrospect, that the lizards' primary defense would be aimed against their main enemy, the viper. "In the Aegean, vipers are specialized lizard predators," said Foufopoulos, an assistant professor at the School of Natural Resources and Environment and the Department of Ecology and Evolutionary Biology. "The only predators that truly matter are vipers," said U-M vertebrate ecologist Johannes Foufopoulos, co-author of a study published online this week in the journal Evolution. Their conclusion? The predator-pressure hypothesis, while generally true, comes with an unexpected twist: Not all predators are created equal. The U-M-led team decided to test the long-held predator-pressure idea using a clever combination of laboratory experiments and field measurements made in mainland Greece and multiple offshore Aegean Sea islands inhabited by different combinations of predators. So from an evolutionary perspective, it only makes sense to maintain tail-shedding ability if there are predators around. However, tail loss carries long-term costs, including impaired mobility, lower social status and slower growth rates. When lizards live alongside lots of creatures eager to devour them, they're more likely to evolve the ability to shed their tails easily, because this trait enables them to survive long enough to reproduce and pass their genes to the next generation. For more than a century, biologists have suspected that this variation is controlled mainly by predator pressure: As the number of local lizard-eaters rises, so does the need for this effective defense mechanism. The ease with which lizards shed their tails varies from species to species and from place to place. Later, the lizard simply grows a new tail. The predator often feasts on the tail while the lucky lizard scurries to safety. When attacked, many lizards jettison the wriggling appendage and flee. Tail-shedding, known to scientists as caudal autotomy, is a common anti-predator defense among lizards.
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