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Wriggle for Your Lives!
Scramble!
Tree-frog tadpoles hatch early to avoid being a cat-eyed snake's lunch.
Frog eggs can't hide, and they can't run either. Or can they? Embryos of the red-eyed tree frog can hatch days early if they feel a snake start to munch on their fellows in a gooey egg sac. The soon-to-be tadpoles sense the vibrations caused by a snake tugging on the egg sac and can distinguish them from vibrations caused by wind or rain.
The world is a dangerous place for tree-frog eggs. Fish and other predators lurk in the water, so the adult frogs lay their eggs on leaves overhanging ponds. But tree leaves aren't safe either; snakes and wasps attack half of egg clutches anyway. To keep from getting eaten, red-eyed tree frog embryos have an escape hatch. They can wriggle out of their eggs and into the water up to 30% prematurely if they feel the characteristic vibrations of a snake attack. Wind and rain can vibrate the eggs at similar frequencies as a snake or wasp, however, and premature tadpoles are more likely to be eaten by fish than full-terms. So the penalty for accidentally hatching
early is high.
Now, integrative biologist Karen Warkentin and colleagues at Boston University have showed how tree-frog eggs distinguish snake bites from rain. First, the researchers embedded an accelerometer in a clutch of eggs to measure the vibrations caused by a snake biting and chewing the eggs. They also measured the vibrations caused by typical bouts of wind and rain. The group then put egg clutches on a mechanical shaker and reproduced the various sets of vibrations. Rain and wind produced vibrations of the same frequencies as those caused by the snake and wasp attacks, but also caused shaking at many other frequencies that tended to damp the snakelike vibrations, the researchers reported this week at a meeting of the Acoustical Society of America in Providence, Rhode Island. The frog eggs rarely hatched when exposed to wind and rain vibrations, but they almost always did during the simulated snake attacks. The frequency of the vibrations also influenced how fast the eggs hatched: If the "snake bites" came more slowly, the eggs waited longer before hatching.
The "work is so tightly controlled that there isn't any room for anyone to doubt" that it is the vibrations that the embryos are responding to, says Peggy Hill, a behavioral ecologist at the University of Tulsa in Oklahoma. Both Hill and Warkentin say that the sensory and information-processing capabilities of embryos need to be examined more closely to unravel how the embryos make this complex decision.
Article from: http://news.sciencemag.org/sciencenow/2006/06/05-02.html
Scramble!
Tree-frog tadpoles hatch early to avoid being a cat-eyed snake's lunch.
Frog eggs can't hide, and they can't run either. Or can they? Embryos of the red-eyed tree frog can hatch days early if they feel a snake start to munch on their fellows in a gooey egg sac. The soon-to-be tadpoles sense the vibrations caused by a snake tugging on the egg sac and can distinguish them from vibrations caused by wind or rain.
The world is a dangerous place for tree-frog eggs. Fish and other predators lurk in the water, so the adult frogs lay their eggs on leaves overhanging ponds. But tree leaves aren't safe either; snakes and wasps attack half of egg clutches anyway. To keep from getting eaten, red-eyed tree frog embryos have an escape hatch. They can wriggle out of their eggs and into the water up to 30% prematurely if they feel the characteristic vibrations of a snake attack. Wind and rain can vibrate the eggs at similar frequencies as a snake or wasp, however, and premature tadpoles are more likely to be eaten by fish than full-terms. So the penalty for accidentally hatching
early is high.
Now, integrative biologist Karen Warkentin and colleagues at Boston University have showed how tree-frog eggs distinguish snake bites from rain. First, the researchers embedded an accelerometer in a clutch of eggs to measure the vibrations caused by a snake biting and chewing the eggs. They also measured the vibrations caused by typical bouts of wind and rain. The group then put egg clutches on a mechanical shaker and reproduced the various sets of vibrations. Rain and wind produced vibrations of the same frequencies as those caused by the snake and wasp attacks, but also caused shaking at many other frequencies that tended to damp the snakelike vibrations, the researchers reported this week at a meeting of the Acoustical Society of America in Providence, Rhode Island. The frog eggs rarely hatched when exposed to wind and rain vibrations, but they almost always did during the simulated snake attacks. The frequency of the vibrations also influenced how fast the eggs hatched: If the "snake bites" came more slowly, the eggs waited longer before hatching.
The "work is so tightly controlled that there isn't any room for anyone to doubt" that it is the vibrations that the embryos are responding to, says Peggy Hill, a behavioral ecologist at the University of Tulsa in Oklahoma. Both Hill and Warkentin say that the sensory and information-processing capabilities of embryos need to be examined more closely to unravel how the embryos make this complex decision.
Article from: http://news.sciencemag.org/sciencenow/2006/06/05-02.html
