ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Amphibian Decline, Why Are Frogs Endangered

Updated on September 5, 2012
Panamanian golden frog, now a critically endangered species
Panamanian golden frog, now a critically endangered species | Source

Amphibians are declining globally

Since the 1980s there has been a drastic decline in amphibian populations, in some locations numbers of a species have crashed and rapidly become extinct. Although animals becoming endangered and extinct is, sadly, a common phenomenon nowadays, this appears to affect amphibians, a class of animals that includes frogs, salamanders and caecilians, to a greater degree than other classes of animals.

In 2004 the first Global Amphibian Assessment, concluded that 32% of the approximately 6000 amphibian species were endangered. It has even been suggested that we might witness the extinction of a whole classification of organisms, something that is unprecedented in the history of this planet. A lot of work is going on to figure out what causes amphibians to be disproportionately affected, and to try to save endangered species from extinction.

Why are frogs and salamanders disappearing?

Some of the reasons for this population decline are the same as those for other organisms, human activity leading to habitat loss and pollution. Amphibians seem to be particularly affected by this because they have distinct stages in their life-cycle, with an aquatic larval stage, like the tadpoles of frogs, and a terrestrial adult form. Hence an adverse change to either to either type of habitat affects them.

Frogs and salamanders are also particularly sensitive to pollution. This is because one of the characteristics of amphibians is their extremely permeable skin. In fact, they do not drink water like other animals. Instead they simply sit in the water and absorb it through their skin. Frog keepers are often advised to avoid holding their pets, in case oils from their hands harm them.

Rabb's Fringe-limbed Treefrog, this is the last known surviving member of its species
Rabb's Fringe-limbed Treefrog, this is the last known surviving member of its species | Source

Does atrazine feminize frogs?

One particular chemical, whose effect on frog populations, and possibly human health, is controversial, is the weed killer atrazine. Tyrone Hayes, a Professor in Berkley University was working as a consultant to Syngenta, atrazine’s manufacturer,when he noticed that, even concentrations that were considered acceptable in water, caused feminization of African clawed frog, Xenopus laevis, males. Hermaphrodite frogs, with both male and female reproductive organs, have been increasing observed in many locations. Obviously feminization stops the males from being able to reproduce and leads to population collapse.

Not all scientists agree with these results and a heated dispute about them is ongoing. Prof. Hayes claims that Syngenta was trying to slow down his research and prevent him from publishing the results, which would harm their product. Syngenta denied that it was attempting to suppress the data, and pointed out that other scientists could not reproduce them.

The rise of frog deformities

Atrazine is still used in the United States, but not in the European Union. However, many frogs in Europe are showing similar gender reversal, presumably because estrogen-like pollutants in the water.

In addition to hermaphrodite frogs, animals with deformities have been observed in increasing numbers. These can include extra limbs, or lacking libs, heart and kidney defects. One theory is that this was caused by the depletion of the Ozone layer and increasing exposure to UVB radiation. Although again scientists cannot agree on the exact results.

Chytrid, the fungal disease that is decimating amphibian populations

Although habitat destruction and man-made pollution account for some of the catastrophic decline of amphibian populations, they cannot explain the whole story. Populations of frogs, such as the golden toad Bufo periglenes , in pristine wild habitats have become extinct. The culprit appears to be a fungus, Batrachochytrium dendrobatidis, commonly known as Bd, or just chytrid. Chytrids are a primitive class of fungi comprising approximately 1000 species, the vast majority of which are quite harmless, living on decomposing organic matter. However Bd, which was first described only in 1999, is a parasite and can wipe out a population in a matter of weeks.

The fungus only affects amphibians, it requires very wet conditions to flourish. Unusually it seems to be able to infect all frog species, most disease causing micro-organisms are more selective. The fungus lives in the skin of amphibians and causes it to harden, by expressing more keratin, the protein found in skin, hair and nails.

This is particularly bad for amphibians because they rely on their very permeable skin to absorb water, and electrolytes. After a chytrid infection they can no longer do that, and often die in a matter of weeks because of electrolyte imbalance which causes heart failure. The disesase can decimate a population of frogs within a few weeks. It has been called “the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and it’s propensity to drive them to extinction" (Gascon et al, 2007).

Xenopus laevis, the Typhoid Mary of chytrid?
Xenopus laevis, the Typhoid Mary of chytrid?

Why is chytrid killing amphibians now?

One of the big questions about chytrid is, why now? Is it a new disease, that has suddenly started attacking amphibians, or has something happened that made the problem much more serious recently. It appears that Bd had been present for a long time in Africa, Japan and North America. One hypothesis is that it was spread to the rest of the world from Africa, carried by the African clawed frogs, Xenopus laevis, sold as pets and are an important laboratory animal. The strange thing about Xenopus is that they are one of the few species of frog that carry the fungus but do not develop the disease. In a way they could act like the “Typhoid Mary’s” of the amphibian world.

Whether that is correct or not, it seems probably that the global trade in amphibians as pets and for research has contributed to spreading the disease. Ironically some conservation projects, which try to rebuild natural populations by re-introducing captive bred animals into the wild, might also have helped introduce the disease to populations where it never existed before. Conservationists might also have have spread the fungus on their boots. “Naïve” populations, that had never experienced the disease before, were hit harder than amphibians that had developed some resistance to the disease. It has also been suggested that climate change is creating conditions which are favourable for the chytrid fungus.

The Amphibian Ark Project, trying to save endangered amphibian species

Whatever the origins of the chytrid disease, it represents a very serious threat to the existence of many species of frogs. In response, the Amphibian Ark project has been set up to try to save many endangered species through a program of captive breeding and sperm freezing in zoos around the world. To preserve at least a captive bred population of various amphibians, which could be introduced into the wild at some stage in the future.

Comments

    0 of 8192 characters used
    Post Comment

    • Bard of Ely profile image

      Steve Andrews 

      5 years ago from Lisbon, Portugal

      Voted up and useful and sharing this at Facebook and on Twitter. Will also send it to Kerry Kriger who runs Save The Frogs, a charity I support and have written about.

    • aa lite profile imageAUTHOR

      aa lite 

      6 years ago from London

      Well, really a lot of animals are in trouble these days, amphibians just more than others. Glad to hear that your local Canadian Species appear to be holding their own.

    • Phil Plasma profile image

      Phil Plasma 

      6 years ago from Montreal, Quebec

      I didn't realize that amphibians were in such trouble. I live near the water and see them fairly commonly; so at the very least the one or two species that are common where I live seem to be doing well.

      For informative hub, thanks for the link to the ark. Voted up and interesting.

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)