Study: Loss of wetland biodiversity increases disease risk in frogs

Dec 03, 2013 by Natalie Van Hoose
Jason Hoverman Credit: Purdue Agricultural Communication photo/Tom Campbell

Amphibians in species-poor wetlands have a higher risk of becoming infected with a virulent parasite than those in wetlands with a rich diversity of species, according to a Purdue University finding that sheds light on how biodiversity moderates the transmission of infectious diseases.

In wetlands with a wide variety of both amphibian and parasite species, Pacific chorus frogs are far less likely to become infected with Ribeiroia ondatrae, a trematode that causes limb malformations in frogs and newts.

"The loss of species diversity has major implications for how harmful and deadly diseases are transmitted in nature," said Jason Hoverman, an assistant professor of vertebrate ecology. "While the risk of getting infected with this trematode is largely a factor of how many trematodes are present in the community, we found that disease transmission is also impacted by the number of host species and other parasite species in the system."

The study addresses a paradox of disease ecology: In highly diverse communities, potential hosts are less likely to become infected with harmful pathogens, even though these communities contain more parasites overall. In complex wetland systems, frogs may carry a greater number of parasites, but hosts and parasites work in tandem to prevent infections by the most virulent pathogens. Reducing parasite diversity as well as host diversity greatly increases a frog's risk of contracting a crippling parasite such as Ribeiroia ondatrae.

The implications of losing biodiversity go beyond wetlands, Hoverman said.

"What is amazing is that we're finding these principles hold true for basically all disease systems, whether human, animal or plant. Because human activities are linked to the loss of biodiversity, there are growing concerns that we could inadvertently influence the emergence of infectious diseases."

About 43 percent of global amphibian populations are declining due to dwindling habitats and a rise in such as ranavirus and Ribeiroia ondatrae. To determine the relationships between disease transmission, amphibian diversity and parasite diversity, Hoverman and researchers from the University of Colorado combined data from 345 wetlands, a laboratory experiment and a controlled outdoor experiment.

"Most disease studies focus either on host diversity or parasite diversity," Hoverman said. "But what we were able to do here was bring those two things together so we could look at the relative contribution of changes in host and parasite diversity on disease risk."

In all three settings, higher host and parasite diversity resulted in fewer Ribeiroia ondatrae infections in Pacific chorus frogs. Increasing the number of amphibian species in a wetland reduced infections by Ribeiroia ondatrae and other parasites, a phenomenon known as the "dilution effect." Increasing the number of other parasite species further reduced trematode infections, highlighting the important role of parasites in regulating , Hoverman said. The most diverse wetlands suppressed transmission of Ribeiroia ondatrae from ramshorn snails – the trematode's intermediate host - to frogs by more than 50 percent.

"We always think about the negative connotations of parasites, but having more parasites is not equivalent to greater ," Hoverman said. "Most parasites are fairly benign. Disease risk is really defined as how many virulent are in a community."

Explore further: Giant anteaters kill two hunters in Brazil

More information: Pieter T. J. Johnson, Daniel L. Preston, Jason T. Hoverman, and Bryan E. LaFonte. "Host and parasite diversity jointly control disease risk in complex communities." PNAS 2013 110 (42) 16916-16921; published ahead of print September 30, 2013, DOI: 10.1073/pnas.1310557110

Related Stories

Richer parasite diversity leads to healthier frogs: study

May 21, 2012

Increases in the diversity of parasites that attack amphibians cause a decrease in the infection success rate of virulent parasites, including one that causes malformed limbs and premature death, says a new University of ...

Study shows how biodiversity can protect against disease

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 ...

Do parasites evolve to exploit gender differences in hosts?

Feb 28, 2012

Some disease-causing parasites are known to favor one sex over the other in their host species, and such differences between the sexes have generally been attributed to differences in immune responses or behavior. But in ...

Do parasites upset food web theory?

Jun 11, 2013

Parasites comprise a large proportion of the diversity of species in every ecosystem. Despite this, they are rarely included in analyses or models of food webs. If parasites play different roles from other ...

Recommended for you

Giant anteaters kill two hunters in Brazil

Jul 26, 2014

Giant anteaters in Brazil have killed two hunters in separate incidents, raising concerns about the animals' loss of habitat and the growing risk of dangerous encounters with people, researchers said.

Study indicates large raptors in Africa used for bushmeat

Jul 24, 2014

Bushmeat, the use of native animal species for food or commercial food sale, has been heavily documented to be a significant factor in the decline of many species of primates and other mammals. However, a new study indicates ...

Noise pollution impacts fish species differently

Jul 24, 2014

Acoustic disturbance has different effects on different species of fish, according to a new study from the Universities of Bristol and Exeter which tested fish anti-predator behaviour.

User comments : 0