Healthy animals avoid sick animals

The recent study that examined how tadpoles respond to disease may have implications for other animals, including humans.

October 14, 1999
Web posted at: 12:06 p.m. EDT (1606 GMT)

The recent study that examined how tadpoles respond to disease may have implications for other animals, including humans. Animals may be able to recognize and keep their distance from diseased animals, according to a recent study.

The research by Yale professor David Skelly, in collaboration with Professor Joseph Kiesecker at Penn State University, indicates that healthy bullfrog tadpoles can distinguish the odors given off by infected tadpoles. When presented with a bullfrog tadpole infected with a contagious fungus that attacks the digestive tract, the healthy tadpoles moved up to a foot away, Skelly said.

If animals can sense the risk of disease and respond to it in a way that reduces their risk, than diseases will spread slower than they would otherwise, he said.

Although Skelly and Kiesecker have only studied amphibians thus far they believe their research may have implications for all animals, including humans.

"Biologists had long speculated that animals might gain an advantage from being able to avoid diseased animals, but there was no experimental evidence," said Skelly, a professor of ecology and evolutionary biology. "If these behaviors are widespread, they could be important in making accurate predictions of the spread of disease."

Healthy bullfrog tadpoles can distinguish the odors given off by infected tadpoles and will keep their distance from diseased individuals.

Skelly and Kiesecker have found that tadpoles are highly sensitive to their environment. The next step of their research will involve determining what chemical signals the healthy tadpoles to steer clear of the infected ones.

"Our understanding of predators and their prey has changed drastically since it was discovered that many kinds of prey animals can change their behavior and even their body shape when they smell nearby predators," Skelly said. "Responding to disease risk may be quite similar from an animal's perspective. In both cases, animals appear to be able to use behavior to reduce the chance that they will be harmed or die."

Kiesecker said grey tree frogs have displayed similar protective behavior to the bull frog tadpoles. "Adults will decide where to lay their eggs based on potential for exposure of pathogens on offspring," he said.

"I am interested in the impacts of disease on other communities. Hopefully people will see this work and say we need to look for these behaviors in our own system."

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