A little stress can be a good thing -- but if you’re a tadpole, more stress might be even better. Tadpoles exposed to stress hormones over several days grew bigger tails -- all the better for fleeing predators, according to a study released Tuesday in the journal Proceedings of the Royal Society B.
Experiments show that stress hormones can actually cause a change in body shape in developing animals, according to the researchers at the University of Michigan.
The researchers collected wood frog tadpoles from 10 ponds and set them up in tanks filled with water, oak leaves and some rabbit chow for food. In some of the tanks they would regularly stick in a tiny cage containing a trapped dragonfly larva, which prey on tadpoles; in the other tanks, the tiny cage would be empty, leaving the water free of perceived predators.
When they’re being attacked, tadpoles release stress hormones that travel through the water and can be picked up by their peers. In the tanks that had caged dragonfly larvae, the researchers would give the insect some fresh, live tadpoles to munch on, and watched what happened to the test tadpoles. When they examined the tadpoles, they found high levels of the stress hormone corticosterone in those exposed to predator warnings.
When the researchers exposed tadpoles to corticosterone in the lab, they found that their tails bulked up under the influence of the stress hormone.
When they took some stressed-out, large-tailed tadpoles and some normal-tailed tadpoles and stuck them in a tank with some hungry dragonfly larvae, the stressed-out tadpoles turned out to be the better survivors. Their bigger tails appear to have helped them swim away from such predators, the researchers wrote.
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