Because the results implicate agriculture, future research can narrow the focus to agricultural chemicals, McCoy said.
"Because we know what chemicals are used at these agricultural sites, we can begin to pin down the chemical cause of these abnormalities by conducting controlled experiments with each chemical alone and in combination," she said.
The researchers gathered giant toads, known scientifically as Bufo marinus, from five sites stretching from Lake Worth to Belle Glade and down to Homestead in South Florida. Bufo marinus is a very large, exotic, invasive, species known to be deadly to small animals. Guillette said the researchers studied the toad in part because they are easy to catch and their large size ensures enough blood for analysis. Also, he said, "they are common in other agricultural areas around the world," which means they are a good generalist species.
One of the sites consisted almost entirely of land devoted to sugar cane or vegetable farms. The amount of farmland declined in three other sites, with the last being entirely suburban. Researchers calculated the amount of farmland in each site using Google Earth images.
Each site was 2.1 square miles, with the toads collected at the center. That's because the toad's home range is known to be about 1.2 miles, and the researchers sought only those toads living entirely within each site. The researchers collected at least 20 toads from each site in 2005 and 2006.
Examination of the euthanized toads revealed a pattern: The more agricultural the land where they lived, the more sexual organ abnormalities or so-called "intersex" toads -- toads who have both female and male internal reproductive organs, not a normal condition for this and most species of amphibians.
While normal male toads'
|Contact: Lou Guillette|
University of Florida