Landmark Study Reveals Low National Rate Of Frog Abnormalities On Wildlife Refuges

Tuesday, November 19, 2013

An unprecedented 10-year-study by the U.S. Fish and Wildlife Service shows encouraging results for frogs and toads on national wildlife refuges. The study, published Tuesday in the peer-reviewed online journal PLOS ONE, finds that on average, less than two percent of frogs and toads sampled on 152 refuges had physical abnormalities involving the skeleton and eyes – a lower rate than many experts feared based on earlier reports.  This indicates that the severe malformations such as missing or extra limbs repeatedly reported in the media during the mid-1990s were actually very rare on national wildlife refuges.

“Frogs and toads are strong indicators of wetland and environmental quality. What affects them affects a broad range of other species,” said Service Director Dan Ashe. “This research significantly advances our understanding of amphibian abnormalities while amassing one of the world’s largest datasets on the issue.”

The study also highlights areas of the country with more abnormal frogs than expected. These areas, termed “hotspot clusters”, warrant further research to determine their causes.

Concern about amphibian abnormalities became widespread in 1995 when middle school students discovered frogs with misshapen, extra or missing limbs at a Minnesota wetland. Since then, scientists have continued to report frogs and toads with severe abnormalities and documented global amphibian population declines, disease outbreaks and an increased rate of species extinctions.

In 2000, Congress asked agencies within the Department of the Interior, including the Service and U.S. Geological Survey, to address growing concerns about the health of amphibians in the United States. In response, the Service launched a 10-year study, the largest ever of its kind, to determine the distribution and severity of amphibian abnormalities within the National Wildlife Refuge System. The research effort – called the National Abnormal Amphibian Program – sampled more than 68,000 frogs on 152 refuges, and in the process, compiled one of the world’s largest databases on amphibian abnormalities.

On average, only two percent of the frogs and toads were classified as having skeletal or eye abnormalities, the types of abnormalities most commonly studied. The expected background range of zero to two percent skeletal/eye abnormalities was found at many refuges. Extra limbs were exceedingly rare:  just 0.025 percent of all frogs sampled.

However, consistent with other, prior studies, the Service’s study detected areas where sites with higher rates of abnormalities tend to cluster together geographically. Within these regional hotspot clusters, which were found in the Mississippi River Valley (northeast Missouri, Arkansas and northern Louisiana), in the Central Valley of California, and in south-central and eastern Alaska, abnormality frequency often exceeded the national average of two percent, affecting up to 40 percent of emerging amphibians in some individual samples.

Analysis of the data showed that the location where the amphibians were collected was a better predictor of whether or not they would be abnormal than was their species or the year they were sampled. There was virtually no evidence that some species were more likely to be abnormal than others or that more abnormal frogs were found in some years than in others.  

Although this study was not designed to investigate the reasons behind amphibian abnormalities, the results strongly implicate localized causes. This is consistent with other research, some of which has identified contamination, predators, parasites or the interaction of these as potential factors.

The complete dataset from the study is being made available online at the Dryad Digital Repository (http://doi.org/10.5061/dryad.dc25r ) to facilitate future research to aid in the conservation of amphibians and their habitats. To view the journal article, visit http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0077467.

For more information on this study visit www.fws.gov/contaminants/Issues/Amphibians.cfm.



"The Bend Beneath Lookout Mountain" Hike And Program Set For March 2

Chickamauga and Chattanooga National Military Park will provide a program at the 18th Ohio Battery positions on Moccasin Bend delving into the artillery battery’s role during the Battle of Lookout Mountain, on Saturday, March 10 at 2 p.m.  This 1.5 mile hike and program will last approximately 90 minutes. Parking will be located near 202 Moccasin Bend Road and “Special ... (click for more)

Getting Back To Our Roots

When you think about TVA, you think about a lot of things: electricity, economic development, flood control, hydropower, dams, navigation, water quality and much more. But did you know that planting trees to improve both the land and water resources in the Valley was a big part of TVA’s primary mission from the beginning? Listed as priority number two on in the TVA Act of 1933, ... (click for more)

Shots Reported At Hamilton Place Mall; Crowds Rush Out In A Panic; No Victims Found

Shots were reported at Hamilton Place Mall shortly after 6 p.m. on Saturday, sending customers at the mall racing out in a panic. Police later said no shooting victims had been found. A call to 911 at 6:07 p.m. said there was an "active shooter." There was a call for EMS to the mall, then another call at 6:10 p.m. of an "active shooter." Those in the vicinity of the mall ... (click for more)

Signal Facing Decisions On Expanding Commercial Area Past Albert Road, Mountain Community Center And Water Service

The design review committee (DRC) of the town of Signal Mountain is in the process of establishing standards for commercial buildings. In the meantime, developer Bob Elliott would like to buy property at the corner of Taft Highway and Albert Road. Albert Road has traditionally been where the commercial property ends. A number of residents in the neighborhood around that area are ... (click for more)

Legislators: Protect Our Students And Teachers

When students step into their classrooms, they are there to learn and prepare for their future. Our teachers serve to advance each student’s education and guide them towards success.  Educators have an additional responsibility: maintaining the trust and respect of their students by conducting themselves professionally and responsibly. The vast majority of our ... (click for more)

Roy Exum: The Saturday Funnies

Every day, without exception, I find a number of “treats” in my daily dose of email. These funnies, and other pertinent information, are sent to me by a myriad of “Internet Buddies” who I repay by sending out some of the funniest that I collect. Think of it as sort of a “co-op” for my readers to enjoy. When The Saturday Funnies began last summer, it was what I still think is ... (click for more)