You are here: home   Blogs   The GOAT Blog   Amphibian alterations
The GOAT Blog

Amphibian alterations

Document Actions
Tip Jar Donation

Your donation supports independent non-profit journalism from High Country News.

Brendon Bosworth | Oct 25, 2012 05:00 AM

Parasites have always filled me with fear. I still experience the occasional bout of night terrors when images of Guinea Worms wriggling out of weeping lesions in my flesh flicker across my dream state subconscious. Over the past few days, while working on a piece for the next issue of High Country News, I’ve become familiar with another parasite whose machinations create an equal sense of repulsion, although it hasn’t kept me up at night. Yet.

This parasite goes by the scientific name of Ribeiroia ondatrae and is a type of flatworm found in freshwater systems. It plays a key role in creating malformed frogs (although it is not responsible for all deformities). Frogs affected by Ribeiroia can sprout extra legs (a frog has been found with eight hind legs) or grow additional flaps of skin between their joints. Dragging around an extra set of limbs tends to make adult frogs unwieldy, making them easy prey for predators, as well as slow to hunt their own food.

“Once they emerge onto land they have a pretty rapid death sentence,” says Pieter Johnson, a disease ecologist at the University of Colorado Boulder, who has recorded parasite-related deformed frogs in 17 states, including six Western states, since he began studying the phenomenon in 1996.

Malformed frogRibeiroia needs three hosts to complete its life cycle. Its first port of call is the water-dwelling ramshorn snail. While inhabiting the snail, it clones itself through asexual reproduction to produce larval minions that swim off to find a tadpole to infect.

“It sounds bad to be a frog, but you really don’t want to be a snail infected with this parasite because then your entire reproductive system gets eaten and transformed, basically into thousands of parasites,” explains Johnson.

Then, Ribeiroia larvae burrow into tadpoles around their limb areas, creating cysts in which they continue to grow. The cysts interfere with limb development, sometimes resulting in the growth of extra appendages. Once a predator, like a heron, has swallowed an infected frog the parasite reproduces inside it, laying eggs the bird expels in its feces, often spreading the little critter to new locations where it starts its lifecycle all over again. Malformed Frog 2

Understanding how the parasite impacts frog populations is important because amphibians are the most threatened group of vertebrates in the world.  In particular, Johnson is researching how nutrient run-off from agricultural fertilizers and cattle grazing can promote algae growth, creating more food for the snail and upping the number of parasite hosts in a system. A loss of biodiversity can also make frogs more vulnerable to infection. This is because some frog species are resistant to the parasite and when the worm attacks them it dies. Having such species in a system means fewer parasites manage to spread to other, more sensitive frogs. Some fish and insects, such as larval dragonflies, eat the parasite so when there are less of these around there could be more parasites too.

Possible ways to keep parasite levels down include planting vegetation around ponds to buffer them from nutrient run-off, and applying fertilizers more efficiently to reduce run-off, says Johnson. As he notes in this video: “I really want to understand how we manage the landscape in such a way as to reduce the types of diseases that can affect and kill amphibians. And if we can figure out how to manage the land in such a way that we can all live together without causing increased amounts of diseases in our wildlife, I think that has enormous applied benefit for keeping these populations viable for generations to come."

Brendon Bosworth is a High Country News intern.

Photos courtesy David Herasimtschuk and

Email Newsletter

The West in your Inbox

Follow Us

Follow us on Facebook! Follow us on Twitter! Follow our RSS feeds!
  1. Rancher vs BLM: a 20-year standoff ends with tense roundup |
  2. Photos of a standoff | Armed militia members join a Nevada rancher to pro...
  3. Why homes are lost to wildfire | This Forest Service expert says it's as much a soc...
  4. The energy haves and have-nots | Will rooftop solar owners get off the grid — and...
  5. The future of the Sacramento Delta hangs in the balance | But few Californians seem to grasp what is at stak...
  1. Why homes are lost to wildfire | This Forest Service expert says it's as much a soc...
  2. Photos of a standoff | Armed militia members join a Nevada rancher to pro...
  3. The energy haves and have-nots | Will rooftop solar owners get off the grid — and...
  4. Will the Colorado River reach the Gulf of California once more? | Photographs of last month's historic water pulses....
  5. Locals resist a Bakkenization of the Beartooths | South-central Montanans oppose new drilling, forew...
More from Flora & Fauna
My chickens lay their own Easter eggs
Backpacking with monster skeeters An Alaska encounter with the fiercest of the 176 mosquito species that roam the U.S.
Best place to see a crowd of grizzlies A few tourists get close to amazing numbers of bears catching salmon at Alaska's McNeil River Falls.
All Flora & Fauna
© 2014 High Country News, all rights reserved. | privacy policy | terms of use | powered by Plone