Mystery of the mutants, Scientists search state for cause of frog deformitiesgreenspun.com : LUSENET : Current News - Homefront Preparations : One Thread
By CINDY HORSWELL Copyright 2002 Houston Chronicle
Whenever rains begin to pour each spring, the serenade begins. To call females to mate, male frogs make croaking noises like someone rubbing an inflated balloon.
For millions of years, this ritual has produced tadpoles that transform into frogs to perpetuate the Southern Leopard species.
But last spring, at least 10 of the Southern Leopard frogs that emerged from the water on national wildlife refuges in Texas and Oklahoma did not fit into the family picture. One had a missing front limb, another had a club foot, and the remaining eight had a withered hind leg.
Brian Cain of Clear Lake, a U.S. Fish and Wildlife Service contaminant specialist, said the frogs were found on four wildlife refuges that were being checked for deformed specimens as part of an ongoing frog study that started two years ago.
Frogs can act as sentinels -- the first line of detection that something could be amiss in the environment -- in the same way a canary is used to detect gas in a coal mine, said the National Wildlife Center in Wisconsin.
Frogs breathe through their skin as well as their lungs and gills. As tadpoles, they are intimately associated with water, and pollutants would be easily absorbed by their sensitive, permeable skin, scientists explain.
Although wildlife refuges are usually pristine, natural habitats, the U.S. Fish and Wildlife Service decided to conduct frog studies on refuges to make sure "no surprises" were found that could harm wildlife and maybe affect humans.
Concern about deformed frogs was first triggered in 1995 when some middle school students on a biology field trip discovered a pond brimming with mutant frogs in a farming community in Minnesota. Half the frogs caught there had extra legs, crippled limbs, missing limbs or sunken eyes.
Since that outing, frog deformities have been documented in 44 states, including Texas, said Ralph Tarmontano, coordinator of the North American Reporting Center for Amphibian Malformations. Minnesota, which has checked 195 sites -- the most of any state -- found a malformation rate statewide of about 6 percent, although at some particularly bad sites the rates ranged from 25 percent to 68 percent. Other states reporting significantly high rates are Vermont, New Hampshire, Wisconsin, Illinois, Michigan, New York, Ohio, Oregon and California.
"But very few systematic surveys have been done anywhere," Tarmontano said, noting that most states have made only spotty, sporadic checks. "But if you look, you will find them as they did in Minnesota, where most of the reports have been made."
The vast majority of Texas has yet to be surveyed, but U.S. Fish and Wildlife hopes its study of the state's 18 wildlife refuges will provide some insight. Before the federal study, deformed frogs had been reported during the early 1960s at a pond near Bryan-College Station, where 5 percent of the bullfrogs there had grown an extra hind leg. Another bullfrog with an extra limb was discovered near the same vicinity in 1997. Then in 1998, a frog with an extra forelimb was found in the Trinity National Wildlife Refuge.
Matt Whitbeck, the refuge's biological technician, had not been searching for deformed frogs at the 13,000-acre refuge on the Trinity River east of Houston when he noticed one walking oddly, "like a spider," four years ago.
But the discovery of the five-legged frog, which was shipped to the University of California at Irvine for examination, helped pique an interest for further investigation on refuges in Texas and around the nation.
The Southern Leopard species was chosen to be surveyed in the national refuge study, Cain said, because the bright green frog with yellow stripes is the one most often found with malformations.
At each refuge in Texas, Cain tries to examine at least 100 young Southern Leopards for possible malformations. He first checks for frog eggs in ponds and waterways after a hard rain and then waits 60 days for the eggs to change to tadpoles and then young frogs. He wants to check for deformed frogs before any sickly ones die or are eaten by predators.
So far, frogs have been surveyed on only six of the state's 18 wildlife refuges. Cain will continue surveying more refuges next spring, including two in Brazoria County near Freeport and one in Jefferson County near Port Arthur.
No deformities were found on three of six refuges examined: Anahuac National Wildlife Refuge east of Houston, Santa Ana National Wildlife Refuge near McAllen and Buffalo Lake National Wildlife Refuge near Amarillo.
"I was kind of surprised that we found none at the Anahuac site, which is located on an old rice field where there had been agriculture chemical use. But maybe the chemicals they use on rice don't have the same effect as those used on other crops," he said.
When the Trinity refuge east of Houston was checked again four years after the first find, only one deformed frog, which had a shortened hind leg, was found out of a hundred examined, Cain said.
And only one deformed frog was found at the Attwater Prairie Chicken refuge near Sealy, west of Houston. "It had a missing leg," said Cain. "It had been dry there, and only a couple of little ponds had frogs to look at."
However, the study set a parameter of finding at least three deformed frogs at a site before the number would be considered significant, Cain said. That only happened in Texas when 4 percent of the frogs examined at Caddo Lake Wildlife Refuge near Marshall were found to have either a club foot or withered limb.
"The Caddo Lake property was once used as an Army ammunition depot for manufacturing gunpowder during the Korean and Vietnam wars. We know a lot of residue from a chemical, perchlorate, was left behind there," said Cain.
Whether the chemical has anything to do with the deformities is unknown, but a study is under way by a graduate student at Texas Tech University, he said.
The most deformities in the region that includes Texas were found at the Deep Fork National Wildlife Refuge in Okmulgee, Okla. A 5 percent deformity rate was found there, but the cause remains a mystery, Cain said.
Nationwide, the most deformities have turned up at refuges in regions such as New England, Minnesota and Alaska, said Tarmontano, whose organization is part of the U.S. Geological Survey.
"It has been surprising. But maybe it's because of a shorter growing period in the North, since it gets cold there so rapidly. The rapid development might make the deformities show up quicker," Cain said. "Or Northern farmers may be using different chemicals on their crops than Southern farmers. We don't know."
Experts now think there could be multiple causes for frog deformities. These include parasites known to burrow into tadpoles, chemicals such as herbicides and insecticides, and increased ultraviolet light radiation from global warming or ozone reduction.
A recently completed study at Penn State University, for instance, found that a flatworm parasite could cause deformed limbs in 2 percent of the frogs in a pond. But when these frogs were exposed to the parasites as well as runoff from agriculture chemicals, the incidence increased to as much as 20 percent.
"We saw a decline in white blood cells of the chemically exposed frogs, which leads us to believe their compromised immune system makes them more susceptible to parasites," said researcher Joseph Kiesecker.
But David Gardiner, a molecular biologist in California who examined the first deformed frog at the Trinity refuge, stressed that other deformed frogs have had no exposure to any parasites.
He has spent the last few years looking at thousands of chemicals found in pond water in Minnesota and has slowly narrowed the list to "three or four compounds" that could be activating the deformities.
Meanwhile, Cain would like to find funding to expand the study beyond the protected wildlife habitats to more urban areas.
Displaying a large toad with five legs recently found in a drainage ditch in a Pasadena neighborhood, he said, "We need to be checking the ditches where our storm water drains. Nobody is even looking at that now."
-- Anonymous, October 27, 2002