Amphibian Study Shows How Biodiversity Can Protect Against Disease – via Herp Digest

Science News, Feb. 13, 2013 — The richer the assortment of amphibian species living in a pond, the more protection that community of frogs, toads and salamanders has against a parasitic infection that can cause severe deformities, including the growth of extra legs, according to a new study by the University of Colorado Boulder.

The findings, published Feb. 14 in the journal Nature, support the idea that greater biodiversity in larger-scale ecosystems, such as forests or grasslands, may also provide greater protection against diseases, including those that attack humans. For example, a larger number of mammal species in an area may curb cases of Lyme disease, while a larger number of bird species may slow the spread of West Nile virus.

"How biodiversity affects the risk of infectious diseases, including those of humans and wildlife, has become an increasingly important question," said Pieter Johnson, an assistant professor in the Department of Ecology and Evolutionary Biology and lead author of the study. "But as it turns out, solidly testing these linkages with realistic experiments has proven very challenging in most systems."

Researchers have struggled to design comprehensive studies that could illuminate the possible connection between disease transmission and the number of species living in complex ecosystems. Part of the problem is simply the enormous number of organisms that may need to be sampled and the vast areas over which those organisms may roam.

The new CU-Boulder study overcomes that problem by studying smaller, easier-to-sample ecosystems. Johnson and his team visited hundreds of ponds in California, recording the types of amphibians living there as well as the number of snails infected by the pathogen Ribeiroia ondatrae. Snails are an intermediate host used by the parasite during part of its life cycle.

"One of the great challenges in studying the diversity-disease link has been collecting data from enough replicate systems to differentiate the influence of diversity from background 'noise,' " Johnson said. "By collecting data from hundreds of ponds and thousands of amphibian hosts, our group was able to provide a rigorous test of this hypothesis, which has relevance to a wide range of disease systems."

Johnson's team buttressed its field observations both with laboratory tests designed to measure how prone to infection each amphibian species is and by creating pond replicas outside using large plastic tubs stocked with tadpoles that were exposed to a known number of parasites. All of the experiments told the same story, Johnson said. Greater biodiversity reduced the number of successful amphibian infections and the number of deformed frogs.

In all, the CU-Boulder researchers spent three years sampling 345 wetlands and recording malformations -- which include missing, misshapen or extra sets of hind legs -- caused by parasitic infections in 24,215 amphibians. They also cataloged 17,516 snails. The results showed that ponds with half a dozen amphibian species had a 78 percent reduction in parasite transmission compared to ponds with just one amphibian species. The research team also set up experiments in the lab and outdoors using 40 artificial ponds, each stocked with 60 amphibians and 5,000 parasites.

The reason for the decline in parasitic infections as biodiversity increases is likely related to the fact that ponds add amphibian species in a predictable pattern, with the first species to appear being the most prone to infection and the later species to appear being the least prone. For example, the research team found that in a pond with just one type of amphibian, that amphibian was almost always the Pacific chorus frog, a creature that is able to rapidly reproduce and quickly colonize wetland habitats, but which is also especially vulnerable to infection and parasite-induced deformities.

On the other hand, the California tiger salamander was typically one of the last species to be added to a pond community and also one of the most resistant to parasitic infection. Therefore, in a pond with greater biodiversity, parasites have a higher chance of encountering an amphibian that is resistant to infection, lowering the overall success rate of transmission between infected snails and amphibians.

This same pattern -- of less diverse communities being made up of species that are more susceptible to disease infection -- may well play out in more complex ecosystems as well, Johnson said. That's because species that disperse quickly across ecosystems appear to trade off the ability to quickly reproduce with the ability to develop disease resistance.

"This research reaches the surprising conclusion that the entire set of species in a community affects the susceptibility to disease," said Doug Levey, program director in the National Science Foundation's Division of Environmental Biology, which helped fund the research. "Biodiversity matters."

The sheer magnitude of the recent study also reinforces the connection between deformed frogs and parasitic infection, Johnson said. Beginning in the mid-1990s reports of frogs with extra, missing or misshapen legs skyrocketed, attracting widespread attention in the media and motivating scientists to try to figure out the cause. Johnson was among the researchers who found evidence of a link between infection with Ribeiroia and frog deformities, though the apparent rise in reports of deformations, and its underlying cause, remains controversial.

While the new study has implications beyond parasitic infections in amphibians, it does not mean that an increase in biodiversity always results in a decrease in disease, Johnson cautioned. Other factors also affect rates of disease transmission. For example, a large number of mosquitoes hatching in a particular year will increase the risk of contracting West Nile virus, even if there has been an increase in the biodiversity of the bird population. Birds act as "reservoir hosts" for West Nile virus, harboring the pathogen indefinitely with no ill effects and passing the pathogen onto mosquitoes.

"Our results indicate that higher diversity reduces the success of pathogens in moving between hosts," Johnson said. "Nonetheless, if infection pressure is high, for instance in a year with high abundance of vectors, there will still be a significant risk of disease; biodiversity will simply function to dampen transmission success."

Story Source:

The above story is reprinted from materials provided by University of Colorado at Boulder.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Pieter T. J. Johnson, Daniel L. Preston, Jason T. Hoverman, Katherine L. D. Richgels. Biodiversity decreases disease through predictable changes in host community competence. Nature, 2013; 494 (7436): 230 DOI: 10.1038/nature11883

Two-legged dog Faith learns to walk

A dog born with two legs has learned how to walk and is bringing hope to disabled soldiers in America.

Published: 10:02PM GMT 18 Dec 2009


The 7-year-old labrador-chow mix was born without front legs.

The puppy and her siblings, also deformed, were rejected by their mother. But Reuben Stringfellow, then 17, came across the tiny animal and brought it home.

He and his mother Jude, an English professor, had to carry the puppy, which they named Faith, for the first few months of her life. But eventually, with patience, and lots of peanut butter as a lure, Faith learned to walk on her two hind legs.

Seven years after her birth, the little yellow dog zips around crowded shops, bustling along with confidence.

Since her first steps in March, 2003, Faith has been a regular guest on US talk shows. She has also become a symbol of hope for injured soldiers.

Ms Stringfellow, who has become a motivational speaker and runs a website devoted to her tiny dog, gets more than 200 letters and emails a day.

Fans of the little dog say she provides inspiration.

"Faith has shown me that different is beautiful, that it is not the body you are in but the soul that you have," Jill Salomon of Montreal, Canada, wrote on the website.

Ms Stringfellow regularly brings Faith to veterans' hospitals across the US to provide hope to disabled soldiers, a mission inspired by her son's service in the US army in Iraq.

Ms Stringfellow told AP that during a recent visit to McChord Air Force Base and Fort Lewis in Washington, the dog brought cheer to soldiers heading off to war, and to those recently returned.

She just walks around barking and laughing and excited to see them all," Jude Stringfellow said. "There is a lot of crying, pointing and surprise. From those who have lost friends or limbs, there can be silence. Some will shake my hand and thank me, some will pat her on the head. There is a lot of quiet, heartfelt, really deep emotion."

http://www.telegraph.co.uk/news/worldnews/northamerica/usa/6841609/Two-legged-dog-Faith-learns-to-walk.html

Frog Deformities: Sign of Parasites on the Rise?

September 22, 2009—You might call it a teenage mutant ninja frog—minus the ninja.

In northern California, foothill yellow-legged tadpoles are developing into juvenile frogs with missing legs and eyes, like the animal seen above in 2008. These deformities are possibly caused by outbreaks of an alien parasite from Eurasia that usually attacks fish used in aquaculture and the aquarium trade, a new study says.

Anchor worms flourished in the South Fork Eel River in 2006 and 2008, when heat waves pushed maximum weekly average water temperatures to 75 degrees Fahrenheit (23.7 degrees Celsius), researchers found. (See map.)

Those years were also drier than normal, corralling tadpoles into smaller pools and making them sitting ducks for parasites.

Once the parasitic crustaceans enter the gills of a tadpole victim, they feed off the tadpole's tissues until male and female parasites mate. The male dies soon after. Meanwhile the fertilized female bores her way partially out of the tadpole.

The female worm's head and part of its body then morph into an anchor-like growth attached to the base of the tadpole's tail or to its legs. The parasite's egg sac is attached to this external growth, but part of the female parasite remains inside the tadpole's body and damages internal tissues.

(Related: "Pesticides, Parasite May Cause Frog Deformities.")

It's unclear whether this damage is responsible for the young Eel River frogs' striking defects, said study co-author Alessandro Catenazzi, a postdoctoral researcher at the University of California, Berkeley. But the team has found that many deformed frogs are infected.

The researchers also noticed that the most common malformations occur in the hind limbs—and in some cases the legs are missing altogether. Missing eyes are rare, he said, with only two cases recorded so far.

Infected frogs also tend to be smaller, making them weaker and less likely to survive the winter, according to the study, led by UC Berkeley's Sarah Kupferberg and published online in August in the journal Copeia.

Throughout California, dam construction and river flow management for irrigation, among other factors, have limited the yellow-legged frog's habitat, leading to a "dramatic decrease" of about 54 percent of the frog's native habitat, Catenazzi said. The frog historically was found from northern Oregon south to the San Gabriel Mountains near Los Angeles, as well as higher elevations in the Sierra Nevada.

The anchor worm is yet another blow to the vulnerable amphibians, the authors say, and climate change is expected to spur more parasite-favoring heat waves in California in the future.

—Christine Dell'Amore

http://news.nationalgeographic.com/news/2009/09/090922-mutant-frogs-missing-limbs.html