Navigation Links
New CU-Boulder study shows diversity decreases chances of parasitic disease

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.


Contact: Pieter Johnson
University of Colorado at Boulder

Related biology news :

1. CU-Boulder team discovers first ancient manioc fields in Americas
2. Nutrient pollution drives frog deformities by ramping up infections, says CU-Boulder study
3. CU-Boulder worm study sheds light on human aging, inherited diseases
4. CU-Boulder technology used to identify unexpected bacteria in cystic fibrosis patients
5. Conservation strategies must shift with global environmental change, says CU-Boulder study
6. Dust in West up 500 percent in past 2 centuries, says CU-Boulder study
7. Regional nuclear conflict would create near-global ozone hole, says CU-Boulder study
8. Low-gravity training machine reduces joint, muscle impacts, says CU-Boulder study
9. CU-Boulder, biotech firm team up on python project in search for human cardiac therapeutics
10. Biological invasions increasing due to freshwater impoundments, says CU-Boulder study
11. As Andean glacier retreats, tiny life forms swiftly move in, CU-Boulder study shows
Post Your Comments:
Related Image:
New CU-Boulder study shows diversity decreases chances of parasitic disease
(Date:10/29/2015)...  The J. Craig Venter Institute (JCVI) policy group ... Biosecurity: Lessons Learned and Options for the Future," which ... Services guidance for synthetic biology providers has worked since ... --> --> Synthetic biology promises great ... pose unique biosecurity threats. It now is easier than ...
(Date:10/29/2015)... -- Connected health pioneer, Joseph C. Kvedar , MD, ... and wellness, and the business opportunities that arise from ... of Healthy Things . Long before health and ... Kvedar, vice president, Connected Health, Partners HealthCare, was creating ... from the hospital or doctor,s office into the day-to-day ...
(Date:10/27/2015)... 2015 In the present market scenario, security ... various industry verticals such as banking, healthcare, defense, electronic ... demand for secure & simplified access control and growing ... hacking of bank accounts, misuse of users, , and ... PC,s, laptops, and smartphones are expected to provide potential ...
Breaking Biology News(10 mins):
(Date:11/24/2015)... ... , ... The United States Golf Association (USGA) today announced Dr. Bruce Clarke, ... annually since 1961, the USGA Green Section Award recognizes an individual’s distinguished service to ... Clarke, of Iselin, N.J., is an extension specialist of turfgrass pathology in the department ...
(Date:11/24/2015)... 24, 2015 /CNW/ - iCo Therapeutics ("iCo" or "the ... results for the quarter ended September 30, 2015. ... dollars and presented under International Financial Reporting Standards ... ," said Andrew Rae , President & ... are not only value enriching for this clinical ...
(Date:11/24/2015)... 2015 /PRNewswire/ - Aeterna Zentaris Inc. (NASDAQ:  AEZS) (TSX: AEZ) ... of the Toronto Stock Exchange, confirms that as of ... corporate developments that would cause the recent movements in ... --> About Aeterna Zentaris Inc. ... Aeterna Zentaris is a specialty biopharmaceutical company engaged ...
(Date:11/24/2015)... ... November 24, 2015 , ... This fall, global software solutions leader SAP and ... to develop and pitch their BIG ideas to improve health and wellness in their ... votes to win the title of SAP's Teen Innovator, an all-expenses paid trip to ...
Breaking Biology Technology: