Curious Cure

Scientists have done plenty of studies investigating how pesticides and fungal infections affect frogs. But what happens when a frog gets hit by both at once? In a new study, researchers have found that one pesticide can actually help the animal by wiping out the infection.

The team studied the fungicide thiophanate-methyl (TM), which is frequently used in Mississippi and Tennessee. So far, researchers don’t know much about how TM affects frogs. They do know that amphibians are vulnerable to infections of the fungus Batrachochytrium dendrobatidis (Bd), which can kill adult frogs and stunt larvae’s growth.

The researchers collected clutches of southern leopard frog eggs in Tennessee and infected some tadpoles with the Bd fungus. Next, the team exposed some of the infected and uninfected tadpoles to TM.

Tadpoles exposed to both Bd and TM showed no signs of fungal infection, the team found. TM-treated tadpoles were also bigger and heavier than those that hadn’t been exposed to the fungicide. Tadpoles infected with Bd and then exposed to TM were the biggest and heaviest of all the groups.

It’s not clear why TM would make the larvae grow more. “To date, no other pesticide has been found to promote life history traits such as mass and size without any obvious costs,” the authors write in PLoS ONE. TM might influence production of hormones, they speculate. And frogs whose infections were cleared by TM might have eaten more afterward to compensate for weakness brought on by Bd. More research is needed to figure out whether TM affects other processes such as reproduction, the team says. Roberta Kwok | 22 August 2012

Source: Hanlon, S.M., J.L. Kerby, and M.J. Parris. 2012. Unlikely remedy: Fungicide clears infection from pathogenic fungus in larval southern leopard frogs (Lithobates sphenocephalus).

Image © Sashkinw | iStockPhoto.com

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