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Shrewd Snake Savors Deadly Meal
16 November 2007 (All day)
Your mother may have warned that you'd get a tummy ache if you scarfed down your food, but for one Australian snake, eating too fast could be deadly. The death adder dines on frogs, but some of them are poisonous. So the snake has learned patience: After striking a particular poisonous frog, it waits for its victim's toxin to degrade before it dines. The finding could help ecologists decipher how one species can outevolve another.
The death adder stabs unsuspecting frogs with its fangs, injecting venom to kill its supper. The frogs have fought back, however, evolving various defenses--longer legs for bigger jumps or chemical substances that taste nasty and can kill. Ecologists Ben Phillips and Richard Shine, both of the University of Sydney, Australia, decided to study the snake's general feeding behavior. And when they did, they stumbled upon a strange twist in this evolutionary arms race.
The team dropped frogs of various species in the snakes' glass pens and kept a video camera rolling to record the action as the snakes captured their prey. The snakes gobbled up nontoxic frogs right after injecting them with venom, but they took more time with two other species, the researchers report in the December issue of The American Naturalist. The snake waited 10 minutes before munching on the marbled frog, which produces a gluelike substance on its skin when irritated. (Mouth full of goo? No, thank you!) Further studies revealed that the gunk loses its stickiness after 10 minutes. The snakes waited even longer--40 minutes--before eating the deadly Dahl's aquatic frog. Shine says that by letting the frogs' chemical defenses break down, the snakes have found an unbeatable strategy. "Any predator eating prey whose defenses will terminate after death can simply wait around," Shine says.
The results reveal an unusual adaptation on the part of the snakes, says Wolfgang Wüster, a zoologist at Bangor University in the U.K. He says the frogs may find another strategy to continue the evolutionary battle: "It is hard to say, however, how it would happen easily."