Amphibian Malformations & Parasites
Parasites have been shown to cause developmental malformations in several amphibian species, most notably in frogs. The predominant parasite linked to amphibian malformations is the trematode worm Ribeiroia ondatrae, which uses amphibians as secondary hosts to complete their life cycle (see Blaustein and Johnson 2003). Free swimming Ribeiroia find host amphibians in ponds and form cysts that can disrupt metamorphic limb formation and produce malformations such as extra limbs (Blaustein and Johnson 2003). Although parasites have been definitively linked to malformations, recent work has identified that parasites do a poor job of explaining many types of malformations, such as those most frequently reported in wild amphibian populations (Skelly et al. 2007; Lannoo 2008). For example, extra limbs are the most commonly produced malformations in laboratory studies of Ribeiroia infections. However, field reports of many species (for example, Ranids and Bufonids) more frequently report missing limbs, missing digits, and cutaneous fusions than extra limbs and digits. Moreover, because parasites naturally occur in many wetlands, the recent increase in the number and breadth of amphibian malformations globally suggests that other, novel factors are responsible for the increase in malformations, or that the historic balance of amphibian hosts and their parasites is being disrupted (Johnson et al. 2007).

Amphibian Malformations & Parasites

  • Deformed Amphibian Research at Hartwick College
    • Description: Discusses four major hypotheses concerning amphibian deformities: chemical pollution, ultraviolet radiation, parasites, and predation. Each hypothesis is outlined and examined; the researchers present their case for parasites and predation as the most likely causes for the majority of reported deformities.
      Resource Type: Case Studies, Issue Overviews
      Resource Format: URL
      Publisher: Hartwick College
  • Ecological Monitoring and Assessment Network (EMAN) Protocols for Measuring Biodiversity: Parasites of Amphibians andReptiles
    • Description: Parasites comprise a vast diversity of organisms that are specifically adapted to living in, or on, another living organism (the host). Over 50% of described organisms can be classified as parasites (Price, 1980). They are metabolically dependent on the host for survival, and feed and reproduce at the host’s expense. The parasites of amphibians and reptiles comprise a diverse array of phylogenetically distinct taxa. In this report we first review the advantages to studying herps and their parasites, review the diverse parasite taxa one can expect in herps, and then provide detailed sampling and quantification procedures for the parasites of reptiles and amphibians. The focus in this study is on the herps of North America, especially those encountered in Canada.
      Resource Type: Recommended Practices
      Resource Format: URL
      Publisher: Malaspina University-College
  • Effects Of Malathion On Embryonic Development And Latent Susceptibility To Trematode Parasites In Ranid Tadpoles (PDF, 5 pp., 70.95 KB)
    • Description: We investigated the effects of embryonic exposure to the widely used organophosphate malathion (15-600 g/L) on the early development and latent susceptibility of pickerel frog (Rana palustris) tadpoles to the trematode parasite Echinostoma trivolvis. The latent effects of contaminant exposure are rarely examined but could have important implications for individual survival and population viability. Our research identifies embryonic development as a sensitive window for establishing latent susceptibility to infection in later developmental stages.
      Resource Type: Journal Articles
      Resource Format: PDF
      Publisher: San Fransisco State University, Environmental Studies Program
  • CollapseParasite Infection and Limb Malformations: A Growing Problem in Amphibian Conservation
    • Description: Suspected causes of amphibian malformations are ultraviolet radiation, pesticides, retinoids, and parasites. Human impacts may alter the natural environment causing changes to any of these suspected causes. The focus here is on parasites in particularly trematodes (Ribeiroia). "Here we evaluate two issues concerning Ribeiroia infection and amphibian limb malformations. First we ask if parasite induced malformations in amphibians have increased in frequency, severity, or geographic prevalence." Then "we assume that an increase [...] has occurred, and we investigate the most likely causal factors" particulary human impacts (taken from the chapter).
      Resource Type: Illustrations (Biological), Issue Overviews, Life Histories and Species Profiles
      Resource Format: PDF, URL
      Publisher: University of California Press
  • Proximity to Pollution Sources and Risk of Amphibian Limb Malformation
    • Description: A study in Vermont looked at frogs in 42 wetlands for causes of limb malformations. The systematic surveys "provide support for the role of chemical toxicants in the development of amphibian limb malformation and demonstrate the value of an epidemiologic approach to this problem" (from the summary).
      Resource Type: Issue Overviews, Journal Articles
      Resource Format: PDF, URL
      Publisher: Environmental Health Perspectives
  • Sublethal Impacts of Coal-Derived Trace Elements on Amphibians, Reptiles, and Invertebrates
    • Description: Information about research on a series of projects intended to determine how the physiology, behavior, and morphology of organisms are modified by exposure to coal-derived trace elements. Currently, studies are underway to determine the effects of coal combustion wastes on: 1) hormone cycles in eels (Anguilla rostrata) and slider turtles, 2) genetics and physiology of mosquito fish (Gambusia affinis) and snails (Campeloma decisum), 3) susceptibility of largemouth bass (Micropterus salmoides) and water snakes (Nerodia taxispilota) to parasitic infections, and 4) energetics of limb regeneration in crayfish (Procambarus acutus).
      Resource Type: Issue Overviews
      Resource Format: URL
      Publisher: Savannah River Ecology Laboratory, University of Georgia
  • Synergism between trematode infection and pesticide exposure: A link to amphibian limb deformities in nature?
    • Description: Discussion of results from a field study and laboratory experiments linking increased trematode infection, and higher rates of limb malformations in amphibians, with increased exposure to pesticides.
      Resource Type: Case Studies
      Resource Format: URL
      Publisher: National Academy of Sciences
  • United States Fish and Wildlife Service Division of Environmental Quality: Amphibian Declines and Deformities
    • Description: This U.S. Fish and Wildlife site about amphibian declines and deformities presents information such as fact sheets, news publications, photographs, and covers topics such as standard operating procedure for abnormal amphibian surveys, abnormality classification; water quality; amphibian populations on national wildlife refuges. Also provides Links to amphibian decline and abnormality sites and information.
      Resource Type: Bibliographies and Web Indexes, Image Galleries, Issue Overviews
      Resource Format: URL
      Publisher: United States Fish and Wildlife Service