Amphibious Assault

The challenge of being a frog, toad or salamander in today's world

02-01-2003 // Mark Cheater

IT'S GETTING HARDER and harder to be an amphibian. Toads, salamanders and frogs are in decline worldwide from causes such as ultraviolet radiation and disease. Now scientists have added evidence for two more threats to our cold-blooded friends: habitat fragmentation and a popular weedkiller.

In one experiment, researchers in Missouri looked at the dispersal of young salamanders and American toads from pools between forests and cleared fields. They found that most of the toads and spotted salamanders moved toward the forest and avoided the field. They attribute this to higher temperatures and the abundance of predators in the field. If young forest-dwelling amphibians won't cross clearings, it poses a problem for their survival in fragmented habitats. Movement of young, says biologist Betsie Rothermel of the University of Missouri-Columbia, "is the means by which declining populations maybe be rescued or recolonized following extinction."

In another experiment, scientists from the University of California-Berkeley found that a common herbicide demasculinizes native leopard frogs. The herbicide, atrazine, causes males to develop egg cells in their testes, essentially turning them into hermaphrodites. Atrazine, used on crops such as corn and soybeans, is the most widely used herbicide in the country. "Atrazine is potentially destroying biodiversity," says Tyrone Hayes, a biologist at Berkeley who led the study. "In my opinion, this is an unacceptable risk."

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