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Geese May Be Helping to Spread Frog-Killing Chytrid Fungus

The views expressed are those of the author and are not necessarily those of Scientific American.

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canada goose belgiumThe frog-killing fungus Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis, has been blamed for about 100 amphibian extinctions around the globe since it was first observed in 1998, but clear information on exactly how it spreads has remained a mystery.

Now a team of scientists working in Belgium have come up with one potential clue: the chytrid fungus may sometimes be carried to new habitats on the toes of waterfowl such as geese.

According to research published April 13 in the journal PLoS One, geese are “potential environmental reservoirs” for the Bd fungus, because waterfowl and amphibians often co-occur in the same habitats. The team studied 497 wild geese—which had been rounded up from six wildlife areas in East Flanders as part of an invasive species eradication program—and found that the keratinous toe scales of 76 of the birds tested positive for Bd. The fungus was present on both species of geese that they tested: invasive Canada geese (Branta Canadensis) and domesticated geese (Anser anser domesticus) that had been living in the wild.

The researchers then took some toe scales, heated them in an autoclave, and exposed them to Bd zoospores, which over the course of the in vitro experiment both adhered to and proliferated on the toe cells. After four days, the fungus developed discharge tubes and released new zoospores, showing that the geese’s toe scales provided not just a site for the fungus to reside but also to reproduce.

The team also incubated Bd zoospores on the surface of toe tissue from a dead whooper swan (Cygnus cygnus) and two dead Moscovy ducks (Cairina moschata) that had been brought to their facility for postmortem examination, with similar results.

frog killed by chytrid fungusWhereas Bd thrives in moist environments, the paper points out that it can survive a drying period of up to 30 minutes, during which time a goose could fly up to 30 kilometers—more than enough time for a bird to move from one pond to another.

The researchers did add two caveats: first, because the in vitro experiment used scales from destroyed birds that had been heated in an autoclave, the tissue may have been altered in the process, although they saw no specific macroscopic evidence of such. Second, they note that direct contact between amphibians and geese “might be rather limited.”

Although this research does not prove avian-to-amphibian fungal transmission, it appears to be an important step into understanding the possible transmission paths of this deadly fungus.

Read my previous stories on the chytrid fungus here.

Photo 1: An invasive Canada goose in Belgium by Peter Van den Bossche. Photo 2: A dead frog infected with Bd by Brian Gratwicke. Used under Creative Commons license

John R. Platt About the Author: Twice a week, John Platt shines a light on endangered species from all over the globe, exploring not just why they are dying out but also what's being done to rescue them from oblivion. Follow on Twitter @johnrplatt.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Eric Mills 12:56 pm 04/20/2012

    This is troubling news, but certainly sounds feasible.

    A more obvious source of the spread of the fungus would seem to the the worldwide live animal food market trade. Millions of American bullfrogs (most commercially-raised) are shipped around the world annually for human consumption. Many of these frogs are purchased and released into the wild, by ill-informed “do-gooders” or Buddhist religious sects in “animal liberation” ceremonies.

    A 2009 study published in BIOLOGICAL CONSERVATION documented that, of the market bullfrogs necropsied, 62% tested positive for Bd. (These markets were in New York City, Los Angeles and San Francisco.)

    This commerce should be abolished ASAP. Even now, reportedly, the European Union and Australia allow only frozen bullfrog products to be imported for food.

    Here in California (which imports two million bullfrogs annually), the State Fish & Game Commission twice voted unanimously in 2010 to stop issuing permits for live frogs and turtles for the live markets (mostly found in various “Chinatowns”). The Dept. of Fish & Game ignored the commission’s instructions, and continues to issue the permits on a month-to-month basis. When challenged by an irate commissioner, the Dept. responded, “The Director acts at the pleasure of the Governor.” To date, the DFG has received more than 4,000 letters in support of the ban. So much for the democratic process, and any real concern about the environment. The issue has much more to do with politics, image, economics and “culture” issues than resource protection, sadly.

    Eric Mills, coordinator

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  2. 2. John R. Platt in reply to John R. Platt 2:18 pm 04/20/2012

    Absolutely, Eric. Check out my previous articles about chytrid, in particular this one:

    Link to this
  3. 3. kwak66 12:33 am 04/27/2012

    This is a very interesting debate. I think that the geese could have transferred the fungus even if they state that the exact contact with this a goose and frogs may have been minor. It is important to not only learn more about this for the future but also a way to control it so we don’t have a lot of different amphibious species being removed from the ecosystem of different lakes and aquatic habitats. This is a very interesting subject that I recently had in a English paper I typed about the different animals in the world and how each coexist with each other so if one species goes extinct it could cause major problems for another species living in the same ecosystem.

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  4. 4. LMac4 1:28 am 05/2/2012

    The fact that over 100 species of amphibians have gone extinct because of the chytrid fungus with very little media coverage shows that if an endangered species doesn’t have widespread public appeal (eg. pandas), very little in the way of conservation gets done. This is a widespread problem with the decimation of many amphibian and insect species that are critically endangered. There needs to be more publicity surrounding these kinds of environmental issues.

    Link to this

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