Like predators, pesticides morph tadpoles

The world’s most popular weed killer can cause amphibians to change shape in ways normally caused by a predator. In the first study of its kind, scientists demonstrated that sublethal and environmentally relevant concentrations of Roundup caused two species of amphibians to alter their morphology. Their paper is published in Ecological Applications. Rick Relyea, professor of biological sciences at the University of Pittsburgh and director of the Pymatuning Laboratory of Ecology, set up large outdoor water tanks containing many of the components of natural wetlands. Some tanks contained caged predators, which emit chemicals that naturally induce changes in tadpole morphology (such as larger tails to better escape predators). After adding tadpoles to each tank, he exposed them to a range of Roundup concentrations. After three weeks, the tadpoles were removed from the tanks. “It was not surprising to see that the smell of predators in the water induced larger tadpole tails,” says Relyea. “That is a normal, adaptive response. What shocked us was that the Roundup induced the same changes. Moreover, the combination of predators and Roundup caused the tail changes to be twice as large.” Because tadpoles alter their body shape to match their environment, having a body shape that does not fit the environment can put the animals at a distinct disadvantage. Predators cause tadpoles to change shape by altering the stress hormones of tadpoles, says Relyea. The similar shape changes when exposed to the pesticide suggest that it may interfere with the hormones of tadpoles and potentially many other animals. “This discovery highlights the fact that pesticides, which are important for crop production and human health, can have unintended consequences for species that are not the pesticide’s target,” says Relyea. “Herbicides are not designed to affect animals, but we are learning that they can have a wide range of surprising effects by altering how hormones work in the bodies of animals. “This is important because amphibians not only serve as a barometer of the ecosystem’s health, but also as an indicator of potential dangers to other species in the food chain, including humans.”