A recent study by the scientists at the University of Florida has found that uncontrolled agricultural practices could lead to abnormalities in amphibians. A study, with wide ranging implications for a debate over the threat caused by agricultural chemicals, scientists has found that toads in suburban areas are less likely to suffer from reproductive system abnormalities than toads near farms – where some had both testes and ovaries.
“As you increase agriculture, you have an increasing number of abnormalities,” observes Lou Guillette, a distinguished professor of zoology and one of the several University of Florida authors of a paper on the research. The research is headed by Krista McCoy who did the work as part of her dissertation.
Agricultural chemicals are considered to be one likely cause for the worldwide decline of amphibians. A number of studies have reflected upon a link between herbicides used in farming practices and the sexual abnormalities an frogs and tadpoles. Other causes may include pathogenic infections and habitat loss.
Varied research on frogs collected from agricultural areas and other natural areas has been already done. The exploration by the scientists at University of Florida is the first peer-reviewed study to compare abnormalities in wild toads, and a variety of toads from heavily farmed areas to partially farmed and completely suburban areas. This is done to spotlight the difference between the impacts of agriculture in opposition to 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.
The results of the study implicate agriculture and McCoy feels that future generations should narrow their focus to agricultural chemicals. “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 specimens for the study, giant toads known scientifically as Bufo marinus, was collected from five sites, each site was 2.1 square miles, from Lake Worth to Belle Glade and down to Homestead in South Florida; a piece of land devoted to sugar cane or vegetable farms; and slowly the farmland declining in three other sites, with the last being entirely suburban. The researchers collected at least 20 toads from each site in 2005 and 2006.
The results of the study were quite shocking. It revealed a pattern. Toads with high sexual abnormalities or so called “intersex” toads, with both female and male internal reproductive organs were found in those that living in agricultural lands.
While the forelimbs of normal male toads are thicker and stronger than those of their female counterparts, more of the intersex frogs found in agricultural fields had thin, weak forearms. They also had fewer “nuptial pads,” areas of scrappy skin on their feet used to grip females during copulation. The more agricultural the sites became, the more feminised the males’ reproductive organs were. Many had both ovaries and testes.
In cases where the sex was definite, the appearance of the male toad was the most affected. Normal male toads are brown, while females are stippled with brown stripes. However, males from agricultural areas were stippled, looking like females. Both the impacted males and the intersex frogs had less of the male hormone testosterone than normal males, suggesting a diminished reproductive capability.
Guillette and McCoy feel that the results of the study may have important implications not only for other wild species, but also for common man.
“What we are finding in Bufo marinus might also occur in other animals, including other amphibian species and humans,” McCoy said. “In fact, reproductive abnormalities are increasing in humans and these increases could partially be due to exposure to pesticides.”
Source: University of Florida
