BIODIVERSITY AND DISEASE

Credit:  CIA World Factbook.

FROM: NATIONAL SCIENCE FOUNDATION
Biodiversity Protects Against Disease, Scientists Find
The richer the assortment of amphibian species 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.

The findings, published in a paper in this week's issue of the journal Nature, support the idea that greater biodiversity in large-scale ecosystems, such as forests or grasslands, may also provide greater protection against diseases, including those that affect humans.

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 ecologist and evolutionary biologist at the University of Colorado Boulder, and the lead author of the paper.

"But as it turns out, solidly testing these links 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 the enormous number of organisms that may need to be sampled, and the vast areas over which those organisms may roam.

This study overcame that problem by studying smaller, easier-to-sample ecosystems, the scientists say.

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

Johnson and colleagues 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, we were able to provide a rigorous test of this hypothesis, which has relevance to a wide range of disease systems."

The researchers buttressed field observations with laboratory tests designed to measure how prone to infection each amphibian species is, and by creating pond replicas using large plastic tubs stocked with tadpoles that were exposed to a known number of parasites.

All the experiments told the same story.

Greater biodiversity reduced the number of amphibian infections and the number of deformed frogs.

The scientists 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.

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 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.

The researchers found that in a pond with just one type of amphibian, that amphibian was almost always the Pacific chorus frog, a creature that's 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, 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.

The recent study also reinforces the connection between deformed frogs and parasitic infection.

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, remained 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 said.

Other factors also affect rates of disease transmission.

For example, a large number of mosquitoes hatching in a particular year increases 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, then passing on the pathogen.

"Our results indicate that higher diversity reduces the success of pathogens in moving between hosts," Johnson said.

"But if infection pressure is high, there will still be a significant risk of disease. Biodiversity will simply dampen transmission success."

Co-authors of the paper are Dan Preston and Katie Richgels of the University of Colorado Boulder, and Jason Hoverman of Purdue University.

In addition to NSF, the research was funded by the National Geographic Society and the David and Lucile Packard Foundation.

-NSF-

NEW FROG SPECIES FOUND IN NEW YORK CITY

The following excerpt is from the National Science Foundation website:
March 14, 2012
In the wilds of New York City--or as wild as you can get that close to skyscrapers--scientists have found a new leopard frog species.
For years, biologists mistook it for a more widespread variety of leopard frog.
While biologists regularly discover new species in remote rainforests, finding this one in ponds and marshes--sometimes within view of the Statue of Liberty--is a big surprise, said scientists from the University of California, Los Angeles; Rutgers University; the University of California, Davis and the University of Alabama.
"For a new species to go unrecognized in this area is amazing," said UCLA biologist Brad Shaffer, formerly at UC Davis.

Shaffer's research is funded by the National Science Foundation's (NSF) Division of Environmental Biology.

In recently published results in the journal Molecular Phylogenetics and Evolution, Shaffer and other scientists used DNA data to compare the new frog to all other leopard frog species in the region.

"Many amphibians are secretive and very hard to find, but these frogs are pretty obvious animals," said Shaffer.

"This shows that even in the largest city in the U.S., there are still new and important species waiting to be discovered."

The researchers determined the frog is an entirely new species. The unnamed frog joins a crowd of more than a dozen distinct leopard frog species.
The newly identified wetland species likely once lived on Manhattan. It's now only known from a few nearby locations: Yankee Stadium in the Bronx is the center of its current range.

Lead paper author Cathy Newman, now of Louisiana State University, was working with Leslie Rissler, a biologist at the University of Alabama, on an unrelated study of the southern leopard frog species when she first contacted scientist Jeremy Feinberg at Rutgers University in New Jersey.

Feinberg asked if she could help him investigate some "unusual frogs" whose weird-sounding calls were different from those of other leopard frogs.
"There are northern and southern leopard frogs in that general area, so I was expecting to find one of those that for some reason had atypical behaviors or that were hybrids of both," Newman said.

"I was really surprised and excited once I started getting data back strongly suggesting it was a new species. It's fascinating in such a heavily urbanized area."
Feinberg suspected that the leopard-frog look-alike with the peculiar croak was a new creature hiding in plain sight.

Instead of the "long snore" or "rapid chuckle" he heard from other leopard frogs, this frog had a short, repetitive croak.

As far back as the late 1800s, scientists have speculated about these "odd" frogs.
"When I first heard these frogs calling, it was so different, I knew something was very off," Feinberg said.

"It's what we call a cryptic species: one species hidden within another because we can't tell them apart on sight. Thanks to molecular genetics, people are picking out species that would otherwise be ignored."
The results were clear-cut: the DNA was distinct, no matter how much the frogs looked alike.

"If I had one of these three leopard frogs in my hand, unless I knew what area it was from, I wouldn't know which one I was holding because they all look so similar," Newman said. "But our results showed that this lineage is very clearly genetically distinct."
Mitochondrial DNA represents only a fraction of the amphibian's total DNA, so Newman knew she needed to do broader nuclear DNA tests to see the whole picture and confirm the frog as a new species. She performed the work at UC Davis.

Habitat destruction, disease, invasive species, pesticides and parasites have all taken a heavy toll on frogs and other amphibians worldwide, said Rissler, currently on leave from the University of Alabama and a program director in NSF's Division of Environmental Biology.

Amphibians, she said, are great indicators of problems in our environment--problems that could potentially impact our health.

"They are a good model to examine environmental threats or degradation because part of their life history is spent in the water and part on land," Rissler said. "They're subject to all the problems that happen to these environments."
The findings show that even in densely-populated, well-studied areas, there are still new discoveries to be made, said Shaffer.  And that the newly identified frogs appear to have a startlingly limited range.

"One of the real mantras of conservation biology is that you cannot protect what you don't recognize," Shaffer said. "If you don't know that two species are different, you can't know whether either needs protection."

The newly identified frogs have so far been found in scattered populations in northern New Jersey, southeastern mainland New York and on Staten Island.
Although they may extend into parts of Connecticut and northeastern Pennsylvania, evidence suggests they were once common on Long Island and other nearby regions.
They went extinct there in just the last few decades. "This raises conservation concerns that must be addressed," said ecologist Joanna Burger of Rutgers University.
"These frogs were probably once more widely distributed," Rissler said. "They are still able to hang on. They're still here, and that's amazing."

Until scientists settle on a name for the frog, they refer to it as "Rana sp. nov.," meaning "new frog species."