Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Out-of-balance ecosystems play role in demise of amphibian populations

11.02.2004


During the last decade, Val Beasley of the University of Illinois College of Veterinary Medicine has led a team wanting to know why the world’s amphibian populations have been dwindling or riddled with limb deformities.



Evidence from his and other teams points to increasing numbers of common parasites as an important cause. However, the problems facing amphibian habitats really pose a poignant example of ecosystems out of balance because of human activity, according to Beasley, a professor of veterinary biosciences and executive director of the Envirovet Program in Wildlife and Ecosystem Health.

Beasley’s main collaborators, postdoctoral researcher Anna M. Schotthoefer and Rebecca A. Cole, an adjunct professor of veterinary pathobiology at Illinois and scientist with the National Wildlife Health Center in Madison, Wis., say they agree.


A series of their research projects – two published in 2003 and another that will appear as a book chapter this year – dramatically refine the data on parasitic activity and argue that physically and chemically induced changes of aquatic habitats are taking a toll.

“We have to be asking what human activities are contributing to imbalances in these ecosystems to set the stage for more severe infections,” Beasley said. “It’s becoming a serious question of how we can better manage landscapes, streams, wetlands, ponds and lakes. Frogs are among the first animals that young children see in a healthy wild place, but they are not finding them in the same numbers as in past years.”

Tadpoles of many species feed on algae and periphyton – plant slime that grows on other surfaces – converting the material into the protein, fat and other nutrients that are needed by other creatures higher in the food chain, Beasley said. Amphibians are clearly important players in ecosystem functioning, he added.

“The frogs that develop from tadpoles subsequently devour thousands of insects,” he said. “The frogs themselves are also important prey for reptiles, birds and mammals.”

In 1999, two teams of researchers documented in Science that the larval form of Ribeiroia trematodes (parasitic flatworms) cause limb deformities in frogs. The same researchers recently implicated excess nutrients in the water as a contributing cause. While these parasites are to blame for many of the malformed frogs observed, Schotthoefer said, the studies at Illinois indicate that the timing of infection is critically important.

Schotthoefer, in her two studies published last summer, provided the first stage-specific data involving two types of trematode parasites common to frogs, Beasley said.

In the Canadian Journal of Zoology, a team that included Schotthoefer and Cole, working with funding from the U.S. Geological Survey’s Amphibian Monitoring and Research Initiative, showed that about 16 percent of northern leopard frog tadpoles infected with Ribeiroia during the limb-bud stage had major deformities. However, when infected earlier, in the pre-limb stage (two weeks of age), tadpoles suffered massive tissue destruction that resulted in almost 100 percent mortality.

Also last summer, Schotthoefer, Beasley and Cole, in work funded by the U.S. Environmental Protection Agency, found that another parasite, in a group known as echinostomes, is more common than Ribeiroia among the same species of frogs in Minnesota. These parasites attack the kidneys rather than the limb-bud areas of tadpoles.

In the Journal of Parasitology, they reported that when echinostomes attack the kidneys in early development, about one week after hatching, infections lead to the blockage of kidney function and result in a death rate of virtually 100 percent. Tadpoles infected later, after advanced kidneys had developed, survived.

“This all leads to more questions,” Schotthoefer said. “Since there appears to be specific vulnerable periods for infections of Ribeiroia or echinostomes, we need to know whether changing environmental conditions are widening the window of susceptibility.”

It may be that tadpoles are developing more slowly so that they are at the most susceptible stages for longer periods of time than in the past, she said.

“Or are conditions bringing susceptible early life stage tadpoles into contact more frequently with the parasites at critical times so that we are seeing more deformities and, perhaps of greater importance, more rapid die-offs?” she said.

Beasley, who previously documented the presence and impact of echinostomes on cricket frogs in Illinois, said the emerging findings also raise a question about which family of parasites may be of greater importance in terms of amphibian survival. The parasite that attacks the kidneys is far more widespread than the one causing deformities.

A central question is why are more of these parasites being found in frogs. They mature in vertebrate hosts such as birds or mammals or frogs. Their eggs are shed in the feces of the hosts. The eggs hatch and enter snails, where their numbers increase through asexual reproduction. They then emerge into the water to seek out tadpoles.

Research by Beasley, Schotthoefer, Cole and colleagues that focuses on Illinois cricket frogs will appear this year as a chapter of “The Status and Conservation of United States Amphibians,” a book edited by Michael Lannoo of the Indiana University College of Medicine in Muncie and published by the University of California Press.

In the study funded by the John G. Shedd Aquarium and Chicago Zoological Society, Beasley’s team noted that Midwest landowners excavate their ponds so that deep water prevents the establishment of aquatic plants.

Such a practice allows for easier boating, swimming and fishing, but by eliminating aquatic plants, the habitat becomes structurally barren. Herbicide use also aggravates the problem and produces chemical changes. Plant-derived oxygen is reduced, and herbicides also may have direct toxic effects on tadpoles and other animals, Beasley said.

“These changes may set the stage for more severe trematode infection,” he said. “In this study, herbicide impacts on aquatic plants were associated with an increased frequency of severe trematode infection in the kidneys of tadpoles.”

The lack of vegetation also may expose tadpoles to more trematodes coming from the infected snails, because the tadpoles can’t hide or use the vegetation to brush off the parasites, Schotthoefer said.

So while the parasites seem to contribute to declines and deformities in frog populations, the challenge is to find management approaches that put balance back into amphibian ecosystems, Beasley said.

“What are the natural controls of these parasites? Can we re-establish them?” Beasley said. “Are there things missing or reduced from these ecosystems that used to eat both the snails and the larval form of the trematodes? Are there plants missing that are needed to provide both oxygen and cover?

“In all likelihood, we are seeing concurrent changes in all of these factors, and they may have additive or synergistic effects, resulting in increased parasite infections and associated impacts on amphibians,” he added. “Re-establishing the structural and biological diversity of amphibian habitats is clearly worth a closer look.”

Jim Barlow | UIUC
Further information:
http://www.news.uiuc.edu/news/04/0210frogs.html

More articles from Ecology, The Environment and Conservation:

nachricht Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.

nachricht 100 % Organic Farming in Bhutan – a Realistic Target?
15.06.2018 | Humboldt-Universität zu Berlin

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>