Featured Research

from universities, journals, and other organizations

Amphibian Diversity Decreases Chances Of Parasitic Disease, Study Shows

Date:
October 22, 2008
Source:
University of Colorado at Boulder
Summary:
A new study showing that American toads who pal around with gray tree frogs reduce their chances of parasitic infections known to cause limb malformations has strong implications for the benefits of biodiversity on emerging wildlife diseases.

A new University of Colorado at Boulder study shows that American toads who mingle with gray tree frogs reduce their chances of being infected by an aquatic parasite that causes limb deformations, a finding with implications for the benefits of biodiversity on emerging wildlife species.
Credit: Pieter Johnson, University of Colorado

American toads who hang out with gray tree frogs reduce their chances of parasitic infection, limb deformation.

Related Articles


A new University of Colorado at Boulder study showing that American toads who pal around with gray tree frogs reduce their chances of parasitic infections known to cause limb malformations has strong implications for the benefits of biodiversity on emerging wildlife diseases.

The experiments showed that when the toad tadpoles were raised in tanks with the parasitic trematodes -- tiny worms whose larvae burrow into tadpole limb regions and disrupt normal leg development -- 40 percent of the emerging frogs became deformed, said CU-Boulder Assistant Professor Pieter Johnson. But when the toad tadpoles were joined in the tanks with gray tree frog tadpoles, parasitic infections in the toads dropped by almost half, said Johnson, lead author of the study.

The study showed tree frog tadpoles acted as "sponges" for the trematode parasites, which were subsequently killed by the immune systems of frog tadpoles, said Johnson. As a result, fewer parasites were available to infect and cause malformations in the toads. Both the gray tree frog and American toad are broadly distributed in the Midwest and eastern United States and often occur in the same wetlands, he said.

"This is one of the first experimental studies to definitively show that an increase in diversity of host species actually can reduce parasite transmission and disease," said Johnson of CU-Boulder's ecology and evolutionary biology department. Published in the October issue of Ecology Letters, the study has implications for the declining global diversity of wildlife species that are susceptible to parasitic infections, said Johnson.

Other research has shown that a decrease in diversity in mammal host species for ticks carrying Lyme disease increases the risk of Lyme disease in humans, Johnson said. Similar relationships between wildlife diversity and disease prevalence have been suggested by other researchers to influence other vector-borne diseases, including West Nile virus, tick-borne encephalitis and bubonic plague, he said.

"In the absence of parasites, the toads and frogs are pure competitors," Johnson said. "But when trematode parasitism is present in the ecosystem, the adage 'the enemy of my enemy is my friend' comes into play for the toads, which are essentially shielded from infections by the tree frogs." Co-authors on the Ecology Letters study included Richard Hartson from the University of Wisconsin-Madison and Donald Larson and Daniel Sutherland from the University of Wisconsin-La Crosse.

The researchers also ran experiments involving American toad tadpoles coupled with green frog tadpoles, and others involving American toads, eastern tree frogs and green frogs together in the same tanks, said Johnson. In the tanks containing toad tadpoles and green frog tadpoles, the toad tadpoles had similarly high infection rates to those shown when they were the only tadpoles in the tanks.

But when all three tadpole types were raised together, the toad tadpoles were once again buffered from the parasites by the "dilution effect" provided by tree frogs. "Thus, the important determinant of parasite transmission was not total host diversity but the specific composition of the host community," wrote the authors.

The trematode has a complex life cycle involving snails, amphibians and predators. Host snails release parasite larvae into the water, infecting amphibians and causing deformations. Deformed toads and frogs rarely survive long in the wild because of their susceptibility to predators like wading birds, which ingest them and later defecate into wetlands, releasing trematodes to infect other snails and completing the life cycle.

As few as 12 trematode larvae, known as cercariae, can kill or deform a single tadpole by forming cysts in its developing limbs, causing missing limbs, extra limbs and other severe malformations, Johnson said. A 2007 CU-Boulder study led by Johnson showed high levels of nutrients like nitrogen and phosphorus used in farming and ranching activities fuel trematode infections in North American amphibians by hiking the abundance and reproduction of the snail species that hosts trematodes.

Deformed frogs first gained international attention in the mid-1990s when a group of Minnesota schoolchildren discovered a pond where more than half of the leopard frogs had missing or extra limbs, he said. Since then, reports of deformed amphibians have become widespread in the United States, leading to speculation they were being caused by factors like pesticides, increased ultraviolet radiation or parasitic infection.

A recent study of more than 6,000 species of amphibians worldwide concluded that 32 percent were threatened and 43 percent were declining in population because of causes like habitat loss, pollution and emerging diseases.

The new study was funded primarily by the National Science Foundation.

Johnson was recently awarded a five-year, $875,000 David and Lucille Packard Fellowship to support his studies of emerging diseases in changing environments.


Story Source:

The above story is based on materials provided by University of Colorado at Boulder. Note: Materials may be edited for content and length.


Cite This Page:

University of Colorado at Boulder. "Amphibian Diversity Decreases Chances Of Parasitic Disease, Study Shows." ScienceDaily. ScienceDaily, 22 October 2008. <www.sciencedaily.com/releases/2008/10/081021185059.htm>.
University of Colorado at Boulder. (2008, October 22). Amphibian Diversity Decreases Chances Of Parasitic Disease, Study Shows. ScienceDaily. Retrieved December 18, 2014 from www.sciencedaily.com/releases/2008/10/081021185059.htm
University of Colorado at Boulder. "Amphibian Diversity Decreases Chances Of Parasitic Disease, Study Shows." ScienceDaily. www.sciencedaily.com/releases/2008/10/081021185059.htm (accessed December 18, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Thursday, December 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

When You Lose Weight, This Is Where The Fat Goes

When You Lose Weight, This Is Where The Fat Goes

Newsy (Dec. 17, 2014) Can fat disappear into thin air? New research finds that during weight loss, over 80 percent of a person's fat molecules escape through the lungs. Video provided by Newsy
Powered by NewsLook.com
The Hottest Food Trends for 2015

The Hottest Food Trends for 2015

Buzz60 (Dec. 17, 2014) Urbanspoon predicts whicg food trends will dominate the culinary scene in 2015. Mara Montalbano (@maramontalbano) has the story. Video provided by Buzz60
Powered by NewsLook.com
Rover Finds More Clues About Possible Life On Mars

Rover Finds More Clues About Possible Life On Mars

Newsy (Dec. 17, 2014) NASA's Curiosity rover detected methane on Mars and organic compounds on the surface, but it doesn't quite prove there was life ... yet. Video provided by Newsy
Powered by NewsLook.com
Ivory Trade Boom Swamps Law Efforts

Ivory Trade Boom Swamps Law Efforts

Reuters - Business Video Online (Dec. 17, 2014) Demand for ivory has claimed the lives of tens of thousands of African elephants and now a conservation report says the illegal trade is overwhelming efforts to enforce the law. Amy Pollock reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins