Malformed Frogs

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and Amphibians

Judi Manning

Amphibians have been around since the dinosaurs and had good survival rates with infrequent incidences of malformed frogs dating back to 1740. However, since the 1970s, a worldwide decline has been documented. This is something everyone should be worried about. In 1995, the malformation incidences worsened when approx. 50% of the Northern Leopard Frogs middle school students in southern Minnesota found had missing or extra limbs or were misshapen. Today the reports of amphibian malformations in other parts of North America include the Northern leopard frogs, wood frogs, bullfrogs, green frogs, mink frogs, gray tree toads, Pacific tree frog, spring peepers, American toads, long-toed salamander, tiger salamander, and spotted salamander.

There are 13 species of frogs and toads that live in Michigan. Frogs and toads are in direct contact with the gases and liquid in the air, water, mud and leaf litter. They absorb water and air through their skin, making them more vulnerable to environmental toxins. There is currently a major concern whether or not the malformed amphibians indicate a large environmental problem and one that might put human health at risk.

The reasons for the deformities and decline are highly debated and are an under researched issue all over the world. Without completely understanding the cause(s) of amphibian malformations, the link between malformations and the widespread decline is still uncertain. Scientists cannot agree on one overall cause for the decline of amphibians but all agree more data is needed to show natural population fluctuations and to draw conclusions. Population levels can change yearly or up to every 100 years. Without long-term data, it is difficult to determine if a decline is natural or caused by something in the environment. Most malformations are found in recently metamorphosed amphibians so it is believed they do not reach adulthood. This would also cause a species to decline.

There are several causes for the malformations and decline of frogs, toads, and salamanders, but it is also possible that factors interact. Some of the research and theories:

D. Earl Green, a veterinary pathologist at the National Institutes of Health (NIH) in Bethesda, Maryland is co-author of an article published 7/21/98 in the Proceedings of the National Academy of Sciences. This article detailed the research of scientists from Australia, the United States and the United Kingdom, and their discovery which linked a type of fungus to the killing of the frogs and other amphibians in Central America and Australia. Lee Berger from the Australian Animal Health Laboratory in Melbourne, states "Endangered frogs in high-altitude rainforest streams seem to be the most vulnerable, but we don’t know why." One theory is they believe the frog is gradually dehydrated and suffocates because the fungal growth coats the undersides and legs and in reaction to the fungus, are laying down extra layers of keratin in their skin. The natural process of absorbing oxygen and moisture through their skin is hindered or blocked. Another theory is the fungus is releasing deadly toxin into their body.

This unnamed fungus belongs to a new genus, chytrid, which is related to the earliest fungi. The group of simple, single-cell organisms were previously known to live only in decaying matter and in the tissues of some algae, other fungi, plants, and certain invertebrates and have never been found in living tissues of vertebrates. The researchers exposed healthy laboratory frogs to this fungus; they died within two weeks. They are uncertain as to why this fungus has recently affected the amphibians. Scientists speculate that an underlying viral infection, toxin or environmental change could be making the frogs susceptible to the fungus. They do not know if the fungus is the primary cause of death or is killing animals weakened by other factors, such as UV radiation or agricultural chemicals.

Some feel herpetologists may have spread the deadly fungus in their study of amphibians. As a preventative measure, Tim Halliday of the Open University in Milton, Keynes, who is a director of the Declining Amphibian Populations Task Force, has issued a "code of practice" for field workers to follow when they handle amphibians. Remove all mud and other debris from clothing, traps and vehicles. Scrub all equipment using 70% ethanol solution and disposable gloves. Amphibians should also be quarantined before they are released to new locations.

To date, this fungus has been found in 115 animals from 17 species from Panama and Australia and did not show up between 1987 and 1995 in 13 species that had been studied. This fungus has also been linked to major population declines affecting 10 species of frogs and toads from 10 locations in Australia, 7 species from two locations in Panama, a toad from southern California, and 6 species of frogs in four American zoos and aquariums. This is the first evidence that a deadly microorganism is causing the global decline.

There is now evidence that a naturally occurring parasite – a trematode – can alter limb development in amphibians. The parasites form cysts in amphibian limb buds that can disrupt limb development and cause a range of deformity types. Some scientists are questioning whether the parasite hypothesis can explain the recent increase in malformation reports.

Malformations are also the result of xenobiotic chemicals – chemicals humans (sometimes excessive) add to the environment – herbicides, insecticides, fertilizers, or by-products of manufacturing. Some insecticides mimic a growth hormone that causes amphibian embryos and larvae to develop abnormally. Scientists are conducting experiments to ascertain if developmental mechanisms are disrupted or altered by these chemicals. Areas with a history of pesticide use in Quebec had an increased number of malformed amphibians. Animals in their breeding areas could be stressed by xenobiotic chemicals and be more susceptible to diseases or parasites.

Others conclude it could be from increased UV radiation because of the planets thinning ozone layer, which breaks down non-toxic chemicals into toxic chemicals. Other causes could be acid rain, pollution, eradication of wetlands, and habitat destruction. Solid evidence to date has been found in only a few cases.

Capturing frogs by commercial business for food and taking them for pets, has also contributed to their decline.

Amphibian populations fluctuate naturally depending upon the environmental conditions such as amount of rainfall, but humans are also likely responsible and exacerbate the natural fluctuations at local, regional, and global levels.

Continuing studies indicate something in the water is causing these deformities. They are looking into specific pesticides, metals, chlorinated contaminants and other chemicals that may be present. More than 10% of the frogs in 54 of Minnesota’s 87 counties have had deformities. Seventy-five percent of the mink frogs, which spend two years in the water developing, are deformed.

David M. Gardiner of Univ. of California, Irvine, feels the same environmental influences that are affecting the development of frogs can also affect people. "If it does it to frogs, It’ll do it to people. There’s no question about that." (Science News)

YOU CAN HELP GATHER DATA

The Wildlife Division of the MI Dept. of Natural Resources is conducting a monitoring program through the Natural Heritage Program, funded through the Non-game Wildlife Fund. The surveys are being conducted by volunteers interested in the decline of frogs and toads in Michigan. The volunteers consist of professional biologists, herpetologists, university personnel, and interested citizens. Each observer has a particular survey route to listen for frogs. This data, gathered over the years, hopefully, will show if there are any population fluctuations.

If you wish to participate in the survey or report amphibian malformations in North America, or if you have handled a large number of amphibians and there were no malformations, contact:

Lori Sargent at (517) 373-1263 or send a note to her at P.O. Box 30444, Lansing, MI 48909-7944 and she will forward them to NARCAM (North American Reporting Center for Amphibian Malformations) or

Call (800) 238-9801 or

Send it to the NARCAM website: http://www.npwrc.usgs.gov/narcam/.

More information on frogs and toads

References:

  1. Introduction to the Malformed Amphibian Issue, North American Reporting Center for Amphibian Malformations, (http://www.npwrc.usgs.gov/narcam/backgrnd/backgrnd.htm) NARCAN 8/27/98
  2. Water Link to Frog Deformities Strengthened. L. Milot, Science News, 10/1/97
  3. A Plague on Frogs, Lybi Ma, Discover, 1/98, Pg 87
  4. Nongame Wildlife Species & Resources, http://www.dnr.state.mi.us/wildlife/Heritage/frogs/default.htm
  5. Nongame Wildlife Species & Resources, htt;://www.dnr.state.mi.us/wildlife/Heritage/frogs/frgartel.htm
  6. Frogs and Toads of MI: Symbol of our Spring or of our Fall? Lori Sargent, Natural Heritage Program, DNR Wildlife Division
  7. A Great Leap Forward, Ian Anderson, New Scientist, 6/27/98 from website (http://www.newscientist.com/ns/98062/frog.

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