March 29, 2000
Agency Contact Phone
E-mail
U.S. Geological Survey Paul Slota or 608-270-2420
paul_slota_at_usgs.gov
Carol Meteyer 608-270-2462
carol_meteyer_at_usgs.gov
NIH-National Institute of Jim Burkhart 919-541-3280
Environmental Health Sciences
University of Wisconsin- Dept. of Anatomy/ Katie Loeffler or
608-263-6321
NIEHS Center for Developmental, Molecular John Fallon
608-262-3775
and Toxicology
X-RAY STUDIES SHED LIGHT ON FROG DEFORMITIES
Editors: For a link to reproducible pictures and x-rays and to other
amphibian press releases, please go to http://www.usgs.gov/amphibians.html
The most extensive and detailed study of bone changes found in malformed
frogs to date shows that both time- and location-specific environmental
events may influence the development of these malformations, according to a
paper that will be published soon in the journal Teratology. The study
revealed that similar malformations are occurring in frogs collected at the
same time from a particular site, indicating that tadpoles at specific
sites have received the same type of environmental insult at the same
developmental stage.
The data represent 180 frogs collected at 16 sites in three states --
Maine, Minnesota and Vermont -- over two years of study and is the result
of a large multi-agency effort involving the USGS National Wildlife Health
Center, University of Wisconsin Department of Anatomy, NIH-National
Institute of Environmental Health Sciences, Minnesota Pollution Control
Agency, Vermont Agency of Natural Resources, and the U.S. Fish and Wildlife
Service. Key to accomplishing this multi-agency work was a Memorandum of
Understanding between NIEHS and USGS
Since middle-school students on an outing discovered large numbers of
deformed frogs in a Minnesota pond in 1995, the dramatic increase in recent
reports of malformed frogs has drawn the attention of scientists and the
public. Malformed frogs are now documented in 44 states, in 38 species of
frogs and 19 species of toads, with estimates of deformities as high as 60
percent in some local populations. Scientists now agree that current
numbers of reported malformations exceed any norm and that the situation
warrants urgent attention. These die-offs and deformities of amphibians
around the globe are of great concern because amphibians are good
barometers of significant environmental changes that may go initially
undetected by humans.
The study, Hind Limb Malformations in Free-Living Northern Leopard Frogs
(Rana pipiens) from Maine, Minnesota and Vermont Suggest Multiple
Etiologies, will be released soon in the journal Teratology, said lead
author Dr. Carol Meteyer, a wildlife pathologist at the USGS National
Wildlife Health Center in Madison, Wisc. The study, said Meteyer,
contributes to the ongoing multidisciplinary analyses of frog malformations
and presents the range, complexity and recurring patterns found in hind
limb malformations in frogs that have survived to metamorphosis -- the
transformation from tadpole to frog -- at several different locations in
the United States.
"These malformations are the result of environmental factors affecting the
frog limb development during early tadpole stages, and this study shows the
wide variety of responses the developing limb can have to these factors,"
Meteyer said. "The precision and patterns of some of these malformations
are striking."
For example, the wildlife pathologist said, two frogs from Minnesota in
1998 were missing a single middle bone from each toe on both feet. Frogs
from the study site in Maine and two sites in Minnesota had bones
duplicated in their hind limbs, primarily in the form of multiple toes. In
addition, the research revealed that although multiple -- or extra -- limbs
were found in only 5 percent of the frogs in the study, all frogs with
multiple limbs came from the two sites in Minnesota and the site in Maine
where frogs were also afflicted with multiple toes. No frogs with multiple
limbs, said Meteyer, came from the 13 other sites with malformed frogs,
although the frogs at some of these other sites also exhibited
site-specific deformity patterns.
In Vermont, for example, all of the 65 malformed frogs the researchers
examined were missing all or a portion of their hind legs, but none had
multiple toes or limbs. Of the Vermont frogs missing entire limbs, x-rays
revealed that 73 percent were also missing bones in the hip, providing
evidence that a predator had not removed the limbs, but that developmental
errors were to blame.
"The wide geographic occurrence and the variety of malformations that occur
in free-living frogs," said Meteyer, "suggest that both site-specific and
time-dependent influences may be involved in the development of these
malformations. Since similar malformations are occurring in frogs
collected at the same time from a particular site, it seems that tadpoles
at a specific site have received the same type of developmental insult at
the same stage of development."
The paper also discusses the varied current hypotheses proposed as causes
of malformations in light of the x-ray data presented in this paper.
Several hypotheses are being considered to explain the causes of
malformations, including chemical contamination; infection with
metacercariae, a kind of immature parasitic worm; exposure to the sun's
ultraviolet rays; and physical trauma. Based on the x-ray data presented
in the Teratology study, Meteyer and her colleagues feel that none of the
current hypotheses adequately address the full range of malformations.
"The detailed descriptions and classification presented in this paper will
contribute to the foundation for further multidisciplinary research
designed to provide insights into the causes of malformations in
free-living frogs," Meteyer said.
Scientists at the NIH's National Institute of Environmental Health
Sciences are currently attempting to identify potential
malformation-causing agents in the environment where deformations occur and
are exploring their potential role in this complex problem. Dr. Jim
Burkhart, the biochemist responsible for the NIEHS efforts to evaluate
whether agents present in the water may be contributing to the increase in
frog malformations, said, "The likelihood of multiple causes demonstrated
by this work clearly parallels some of our efforts to evaluate possible
water-borne factors by analysis of water and sediments. We have not
identified single causes of deformities ? however, we have identified
mixtures with the capacity to disrupt development of amphibians and many
other species at several sites that are a part of this study."
Additionally, the USGS National Wildlife Health Center and the University
of Wisconsin's Department of Anatomy/NIEHS Center for Developmental,
Molecular and Toxicology are performing extensive examinations on
wild-caught tadpoles to more clearly delineate the developmental causes of
frog malformations.
As the nation's largest water, earth and biological science and civilian
mapping agency, the USGS works in cooperation with more than 2,000
organizations across the country to provide reliable, impartial, scientific
information to resource managers, planners, and other customers. This
information is gathered in every state by USGS scientists to minimize the
loss of life and property from natural disasters, contribute to the sound
conservation, economic and physical development of the nation's natural
resources, and enhance the quality of life by monitoring water, biological,
energy and mineral resources.
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