Here is the link to the paper in APA format as well:
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Amphibian Malformations & Declines

Christy Flugga (Schlangen)
Fall 2011


The declines and malformation in amphibian are a very important environmental problem that the entire world is faced with. Amphibians are bio-indicators and we need to look at what’s happening to them to make sure something is done so it doesn’t affect us. This project was designed to teach students about how our day to day activities impact the environment in which they live in. They will be taught this through researching topics on the amphibian malformation issue. They will then use what they learned to develop their own experiment to test their findings.


In 1996, I went with my class on a field trip to a local pond for some biological sampling. What we found instead was a disturbing amount of malformed frogs. There were almost fifty frogs with under-formed, missing or extra limbs and eyes. Shortly afterwards we saw news broadcast regarding this issue from other areas across the United States with an abundance of similar malformations. Because of the alarming numbers of malformations and anurans use as bio-indicators, government officials have implemented the national Amphibian Research and Monitoring Initiative (ARMI). “The ARMI goal is to inventory and monitor amphibian populations on federal lands and to evaluate potential causes of declines. An important component of this effort is to develop efficient sampling techniques for the diversity of amphibian types.” (Malformations) During the past decade, a vast amount of research has been undertaken by many organizations. Several variables have been identified as contributing factors towards these malformations. It is my belief that these malformations are a result of multiple causes and that no one sole cause is to blame. “The debate over malformations phenomena is far from conclusive, however, research continues.” (Blaustein A. E., 2011) There are huge concerns over the possible threats to both human and environmental health. This is what has prompted more intensive research by many organizations. Much of the research has focused on these potential causes: chemical contamination, UV-B radiation, sub-lethal predation, and parasite infection. Sampling methods are a requirement to determine the diversity in Anuran populations and should be conducted in various habitat types. Amphibians have more extinct and/ or declining species than with any other class of vertebrates. This research paper is intended to serve as a resource for people to learn about these malformations and their causations.

Malformations were first noticed around 1995, numerous reports started coming in and generated widespread distress among scientists, health officials, public, state and federal agencies. The majority of these malformations involved limb deformities which included: “extra limbs, partially and completely missing limbs, and a variety of other limb malformations (e.g., skin webbings, bony triangles) comprised of many of the observed deformities.” (Burkhart, 1998) This environmental issue is still an area for concern today and new sites, containing malformations, continue to be discovered annually.

Disease emergence and the loss of biodiversity are two of the most urgent environmental difficulties confronting our society. We are responsible for many of these issues, since we are the ones who made changes within their environment. “Although changes in the levels of biodiversity and infectious diseases have often been studied separately, the importance of reciprocal interactions between them has received comparatively little attention. Under what circumstances will disease epidemics drive species losses? (Johnson P. E., 2001) Can higher levels of biodiversity reduce these malformations in amphibians?


Amphibians are the most threatened class of vertebrates.Besides the loss of habitat, infectious diseases are a driving force behind their declines. “Because of their biphasic life cycle, which typically involves an aquatic larval stage and a semi-terrestrial adult, amphibians are assaulted by a variety of pathogens including fungi, flatworms (trematodes), tapeworms (cestodes), roundworms (nematodes), bacteria and various protozoa.” (Degitz, 2003) Bio-indicators are used to examine the health of an ecosystem. Amphibians are bio-indicators because of their makeup and life cycles. Amphibians show us how environmental changes have had an effect on the frequency and intensity of different pathogens.

Digenetic trematodes are parasitic flatworms that have a very complex life cycle that involve different hosts. Species in the genus Ribeiroia use three hosts: planorbid snails, larval amphibians or fishes, and birds or mammals. Planorbid snails are the first host where the parasite performs asexual reproduction. Free-swimming cercariae are the result of this reproduction. Cercariae encyst in the developing limbs of larval amphibians for the resting stage (metacercariae). This resting stage has been linked to the interference of amphibian malformations. The final stage of its life cycle involves the infected malformed amphibian being consumed by an avian or mammalian host. Avian hosts tend to be herons, raptors, or waterfowl. Here the adult parasite then reproduces sexually releasing the eggs in with the host feces. These eggs hatch in an aquatic environment, becoming free-swimming miracidia. The Miracidia theninfect planorbid snails, continuing the cycle. The malformations increase the chances of infected frog’s predation and enhance the transmission of Ribeiroia between their amphibian and bird hosts. There are also many other parasites that have complex life cycles and also alter the appearance and/ or behavior of their second intermediate hosts rendering them vulnerable to various predatory definitive hosts too.

Some of the malformations, that have been seen, occur when ponds contained a particular group of snails called the Rams Horn snail. These snails serve as the ideal first intermediate hosts for a digenetic Trematode called Ribeiroia Ondatrae. Trematode parasites have been used to study these questions in greater detail, “including Schistosoma Mansoni (the causative agent of human Schistosomiasis) and Ribeiroia Ondatrae (the causative agent of amphibian malformations).” (Wilson, 2005) The studies, I have reviewed, indicate that greater levels of diversity have a direct impact in reducing the transmission of parasites to other hosts. Greater diversity in aquatic communities allows for less competent hosts to distract infectious parasites from other more competent hosts, which then reduces the parasites abundance. “Human-mediated introductions of nonindigenous species, including invasive predators, parasites and competitors, are a major contributor to these alarming patterns.” (Smith, 2002) This is supported by various dissections of malformed amphibians from various ponds across the United States that revealed an overabundance of Ribeiroia metacercariae.

Experiments were conducted by various groups to test whether or not Ribeiroia was responsible for the observed malformations. Different groups of laboratory-raised tadpoles were exposed to different numbers of Ribeiroia cercariae and there was a control group used that had zero exposure. These tadpoles were observed through their different stages of metamorphosis. The control group showed high survivorship and no forms of malformation.The tadpoles that were exposed to various amounts of Ribeiroia often died before they reached metamorphosis. The majority of those who survived and completed metamorphosis were severely deformed. The malformations ultimately were similar to those that were reported throughout field observations. What was even more surprising were that, different amphibian species exhibited different malformation with the same amounts of Ribeiroia. There is compelling evidence that links Ribeiroia infection to amphibian malformations. What has not been answered is why the frequency and range of malformed amphibians has been abundantly apparent and not seen to this magnitude prior to the mid 1990’s? Parasite infection explains some of the malformations, but this leaves a secondary factor being responsible for other malformations.

Chemical Implications:

Freshwater ecosystems face many problems, but the biggest threat is eutrophication. Eutrophication is caused by excess nutrient loading through runoff into aquatic environments. This loading is associated with deposits from the atmosphere, fertilizers from local agriculture, farm animals such as cattle and other non-point sources.All of these are highly influential to a trematodes life cycle. This is because eutrophication increases periphyton, which is the preferred food for freshwater snails. “Through a combination of field surveys and experimental research, we have shown that nutrient runoff can enhance Ribeiroia abundance by increasing snail host density and by increasing the number of infectious parasites produced by each snail.” (Locke) Changes in the densities of snails have a direct correlation on the frequencies of malformations. The increase in temperatures also has been linked to the host-parasite interactions. Because they are smaller and have a more efficient metabolic rate, parasites have a strong response to higher temperatures than that of their hosts. In spring, temperatures increase and lead to higher concentrations of these flatworms. This is also the time of year that amphibian larvae are at their most vulnerable state. This leads to increased concentrations of malformations and mortality rates.

The implications of chemical teratogens for human health risks are very relevant when looking at amphibian malformations. If chemicals are involved in the malformations of amphibians, there is a high likelihood for exposure to humans through physical contact, ingestion, and inhalation routes. Studies have shown that, the landscapes that surround wetlands have direct implications on amphibian malformation. Human’s use of land directly places amphibians at an increased risk. “This positive association persists even after adjusting for the effect of developmental stage and variation in water-quality measures such as nitrogen and ph.” (Ouellet, 1997) The proximity of amphibian’s to agriculture has more than doubled their risk of malformations. Studies should include exposure variables that are founded on pollution sources in a logical way in order to accurately correlate malformation rates. There are numerous ways in which chemicals can effect biologic mechanisms and cause deformities. Some studies linked chemical runoff from agricultural runoff and the plasma retinoid levels in amphibians. The retinoids sole function is to signal the pathways for limb development. Other studies have shown that herbicides have an effect on gene expression that signal the development of limbs. A few others have shown that thyroid hormones are designed to protect us against abnormalities during development, and when abnormal chemicals are introduced, it increases the rate for malformation.

Agricultural chemicals, as previously mentioned, have effects on parasite population density and the immune functions of hosts. Both of which, increase the chance of parasite infection. Previous studies failed to take into account all factors that go into measuring water quality. They also forgot to look at the fact that these factors vary and change over an entire season and even a year. Changes are dependent on the sources of runoff, rainfall or the lack thereof and temperatures. With all of these variables, there still were very strong associations between exposures and malformation rates that indicate that these are valid factors in malformations.

The need for awareness:

The disappearance of amphibians will have a deep impact on our wetlands. Amphibians are the most profuse vertebrates in these wetlands. If they disappear it will lead to an explosion of insects. Other animals like reptiles, birds, and mammals would be affected to because amphibians are a staple food source for them. This would result in a devastating food shortage for these species. Students have to understand why the preservation of wildlife is important. Using problem- based methods of learning allow students to think for themselves. They need to know that amphibians have a lot to teach us about science and the environment.

Amphibians have been around for a long time and are source for observing evolutionary success. My guess is that most students would not have attributed the roles of amphibians in ecosystems as important. They need to realize the importance of bio-indicators for ecosystem health. Part of what makes an amphibian an amphibian is the chemicals in their skin and glands for protection. These chemicals can be useful for medicinal purposes. This activity I have developed, will allow students to reflect and investigate real world issues that we use science for. Students can gain an interest in this because it is something they can see in their own backyards by exploring various concepts.

Two groups of students will build model systems to look into parasites roles in these malformations for this environmental issue. Another two groups of students will build different sets of model systems to look into different pollutant types and their roles in malformations. The teacher will be responsible for running the control group to compare the results against. I feel this is a very important lesson for students to because we all impact our environment each and every day. My hope is that with this type of greater awareness will produce more responsible adults in the future.


Anyone that has observed malformed amphibians should report your sightings to: The North American Reporting Center for Amphibian Malformations (NARCAM) by utilizing their online reporting form. Information is also available in various malformation reports for your state or certain deformities. There are various components that lead to the malformations in amphibian populations. Land use, developmental stages, parasites, water quality, chemicals and so much more have all been associated with an increase in amphibian malformations. These issues need to be continuously looked at and in more detail to better determine whether or not this is going to be an ongoing problem. A definitive solution needs to be made. No one solution will change this problem overnight. It took years for this problem to develop the severity it has today and it will take many more years to undo all the bad we have done. The Long term consequences of Ribeiroia infections and amphibian malformations need to be looked at for survival of the species. 50% of malformed frogs fail to survive to a sexual mature age, because of predation, starvation, and the lethal effects of Ribeiroia infection on amphibian larvae. These implications are of substantial concerns to our environment and the survival of amphibian species. In the future we need to start studying the effects that our actions have on the environment to be able to evaluate whether or not it is worth the risks doing them.


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