Skip to main content

Rich diversity of species reduces infections and diseases

American toads who hang out with gray tree frogs reduce their chances of parasitic infection, limb deformation. 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.
Credits: University of Colorado at Boulder.

Comments

Popular posts from this blog

Charging Implanted Heart Pumps Wirelessly

Mechanical pumps to give failing hearts a boost were originally developed as temporary measures for patients awaiting a heart transplant. But as the technology has improved, these ventricular assist devices commonly operate in patients for years, including in former vice-president Dick Cheney, whose implant this month celebrates its one-year anniversary. Prolonged use, however, has its own problems. The power cord that protrudes through the patient's belly is cumbersome and prone to infection over time. Infections occur in close to 40 percent of patients, are the leading cause of rehospitalization, and can be fatal. Researchers at the University of Washington and the University of Pittsburgh Medical Center have tested a wireless power system for ventricular assist devices. They recently presented the work in Washington, D.C. at the American Society for Artificial Internal Organs annual meeting, where it received the Willem Kolff/Donald B. Olsen Award for most promising research in

Autism and Eye Contact: Genes very much are involved

We have now a lot of evidence on genetic components in many disorders including neurological in both adults and kids. Autism is one such problem that has many genes involved. Research is still in full swing to find more genes and related pathways. However, one can find autistic features more phenotypically before genotyping. Eye contact is one of them. Studies have shown that autistic kids make less eye contact. This has been shown to have genetic component now. New research has uncovered compelling evidence that genetics plays a major role in how children look at the world and whether they have a preference for gazing at people's eyes and faces or at objects. The discovery by researchers at Washington University School of Medicine in St. Louis and Emory University School of Medicine in Atlanta adds new detail to understanding the causes of autism spectrum disorder. The results show that the moment-to-moment movements of children's eyes as they seek visual information about the

How much people depend on weather reports

Meteorologists on television, radio, online, and in newspapers supply weather reports to the average person over 100 times a month. Surveys demonstrated that the 300 billion forecasts accessed generate a value of $285 per household every year, or $32 billion for the entire United States. Odds are you have already watched one weather forecast today and will probably check out a few more. Accurate, timely forecasts are vital to everyday life, but just how critical may surprise you. Whether at work or play, you probably watch the weather quite closely. Most of us are at the weather person's mercy to know what to wear, what to expect, to prepare for the worst. New research shows the average United States household checks out a weather report more than three times a day. "It impacts pretty much every part of every activity we are involved with for the most part," Jeff Lazo, the director of the Societal Impacts Program at the National Center for Atmospheric Research (NCAR) in B