Pesticide Pollution Creates Toxin-Tolerant Tadpoles

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Whatever doesn’t kill frogs only makes them stronger.

In an experiment, wood frog tadpoles exposed to low doses of the insecticide carbaryl could survive a later high dosage of the chemical better than other tadpoles that had enjoyed a pesticide-free early life.

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This reaction, called induced tolerance, only occurred in tadpoles taken from ponds located away from agricultural fields. Biologists suggested that the tadpoles from ponds that don’t regularly receive pesticide-polluted runoff may have the ability to react to occasional contamination of their homes. However if they hadn’t built up a tolerance, they were more likely to die in insecticide-tainted water than tadpoles from farm ponds.

Amphibians from agricultural areas didn’t build a tolerance in the same way. On the other hand, farm frogs may be experiencing a constant evolutionary pressure from agricultural chemicals. These amphibians didn’t build a tolerance to carbaryl after low-level exposure early in life. Both exposed and unexposed farm frogs died at similar levels from later higher dosages.

However, the farm frog tadpoles that weren’t exposed to carbaryl in the first portion of the experiment were also less likely to die from later high dosages than unexposed frogs from ponds not located near farms.

“Amphibian populations are declining worldwide, and pesticides and insecticides are one hypothesized cause,” said University of Pittsburgh doctoral student Jessica Hua. “So this discovery has promising implications for the persistence of amphibian populations.”

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The results of this Nietzschean nature study were published in the journal Evolutionary Applications.

“This is the first study to show that tadpole tolerance to insecticides can be influenced by exposure to insecticides extremely early on in life—in this case, as early as the embryonic stage,” said study co-author Rick Relyea, a biologist at the University of Pittsburgh.

IMAGE: Wood frog tadpole morphing into a an adult (Brian Gratwicke, Wikimedia Commons)

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