Washington, July 4 : A new study by zoologists at the University of Florida suggests that toads in suburban areas are less likely to suffer from reproductive system abnormalities than those in the vicinity of farms.
The new finding may be significant to the longstanding debate over whether agricultural chemicals pose a threat to amphibians.
"As you increase agriculture, you have an increasing number of abnormalities," said Lou Guillette, a distinguished professor of zoology.
Appearing in the online version of the journal Environmental Health Perspectives, this study is the first to compare abnormalities in wild toads from heavily farmed areas with frogs from both partially farmed and completely suburban areas.
In so doing, it highlights the difference between the impacts of agriculture versus development.
"Our study is the first to explicitly ask, of these two areas of human disturbance, do we see a greater proportion of abnormal animals in one versus another?" Guillette said.
Lead author of the study Krista McCoy, who did the work as part of her UF School of Natural Resources and the Environment dissertation, said that future research could narrow the focus to agricultural chemicals because the findings of the study implicate agriculture.
"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.
For their study, the researchers picked giant toads, scientifically known as Bufo marinus, from five sites stretching from Lake Worth to Belle Glade and down to Homestead in South Florida.
Upon examining the euthanized toads, the researchers found the pattern that the more agricultural the land where they lived, the more sexual organ abnormalities or so-called "intersex" toads.
According to them, toads near farms were more likely to have both female and male internal reproductive organs, which is not a normal condition for most species of amphibians.
While normal male toads' forelimbs are thicker and stronger than those of their female counterparts, more of the intersex frogs only found in agricultural areas had thin and weak forearms.
The study also revealed intersex frogs had fewer "nuptial pads", areas of scrappy skin on the feet that are used by toads to grip females during copulation.
The researchers observed that male toads from agricultural areas looked like females, and many of them had both ovaries and testes.
Apart from that, both the impacted males and the intersex frogs had less of the male hormone testosterone than normal males, suggesting diminished reproductive capabilities.
Guillette and McCoy said the study's results might have important implications not only for other wild species, but also for people.
"What we are finding in Bufo marinus might also occur in other animals, including other amphibian species and humans. In fact, reproductive abnormalities are increasing in humans and these increases could partially be due to exposure to pesticides," McCoy said.