mountain yellow-legged frog, yellow-legged frog
Rich Pedroncelli/AP
A mountain yellow-legged frog in a marsh
near Ebbetts Pass, Calif.

Deformed Frogs Highlight Global Decline of Amphibian Species

September 28, 2009 06:00 PM
by findingDulcinea Staff
The growing number of deformed frogs in northern California is caused by factors similar to those responsible for the rapid decline of frog populations and other amphibians worldwide.

Parasite Threatens Frog Species in California

A new study links the increase of deformed yellow-legged frogs in northern California to the anchor worm, a parasitic crustacean that attacks tadpoles and feeds off their internal tissue. Frogs that have been subjected to the parasite tend to be smaller and weaker, have missing or underdeveloped hind limbs, and in two cases have a missing eye.

The spread of the parasite is due to two main factors. First, dam construction and other human activity have reduced the yellow-legged frog’s habitat by more than half. Second, drier weather, perhaps due to climate change, reduced the pools for tadpoles, increasing the likelihood that they would be attacked by parasites.

The difficulty for the yellow-legged frog is part of a much larger, global struggle for frogs and other amphibians. As many as one third of amphibian species are in danger of becoming extinct due to a combination of loss of habitats, global climate change, and disease, particularly the chytrid fungus.

Background: Amphibians threatened with extinction

The world population of frogs and other amphibian species has been declining at an alarming rate over the past three decades. According to the International Union for Conservation of Nature and Natural Resources’ 2008 Global Amphibian Assessment, 32 percent of the world’s nearly 6,000 known amphibian species are extinct or threatened with extinction.

“Although habitat loss clearly poses the greatest threat to amphibians, a newly recognized fungal disease is seriously affecting an increasing number of species,” concludes the IUCN. “Perhaps most disturbing, many species are declining for unknown reasons, complicating efforts to design and implement effective conservation strategies.”

The chytrid fungus, specifically Batrachochytrium dendrobatidis (Bd), infects keratin, part of a frog’s skin, and hardens the outer layer of skin. Frogs die soon after, though researchers have yet to definitively determine how; the “two prevailing theories are that the fungus produces lethal toxins or that its presence interferes with the exchange of oxygen and carbon dioxide through the skin,” explains HowStuffWorks.

The fungus, which spreads through water and through direct contact between amphibians, ravages populations. According to a 2006 study, where Bd is prevalent, half of species and 80 percent of individuals are expected to die within a year.

Scientists are divided on the issue of whether climate change is responsible for the spread of the chytrid fungus.

Reference: Amphibian Ark

The Amphibian Ark is a program formed by the World Association of Zoos and Aquariums (WAZA), the IUCN/SSC Conservation Breeding Specialist Group (CBSG), and the IUCN/SSC Amphibian Specialist Group (ASG). It takes amphibians from areas threatened by the chytrid fungus and places them into facilities to protect the species from extinction. Its Web site explains the crisis for amphibians and explains how you can help.

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