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Frog Diseases Increasing

July 19, 2012
Image Caption: Infection with trematodes in this leopard frog caused extra legs to grow. Photo by Pieter Johnson, courtesy of Oregon State University

Brett Smith for redOrbit.com – Your Universe Online

In addition to the stresses placed on amphibians, or perhaps because of them, they are now more likely to succumb to debilitating infectious diseases.

In recent decades, disease seems to have taken a more prominent role in the amphibian mortality rate, according to a new study published in Philosophical Transactions of the Royal Society B. Along with climate change, habitat destruction, pollution and invasive species, these creatures are constantly under threat in both their aquatic and terrestrial habitats.

“There´s more and more evidence of the role of disease in the biodiversity crisis, in both amphibians and other types of animals,” said the study´s co-author Andrew Blaustein, a professor of zoology at Oregon State University.

“It´s normal for animals to deal with infectious organisms, often many of them simultaneously,” he said. “But in the face of pollution, a reduced immune response, climate change, evolving pathogens and many other stresses in such a short period of time, many species now simply can´t survive.”

The research team primarily focused their study on the relationship between disease and biodiversity in amphibian communities, which is suffering from around 200 times the background rate of extinction, the report said.

The study, which posited that amphibians could be undergoing a major extinction event, took an alarmist tone. It observed that infectious disease around the world is increasing at an unprecedented rate and is a major factor implicated in the decline and extinction of many amphibian populations.

Infectious disease has long plagued the amphibian population, but the scientists say it is their ability to combat these diseases that is contributing to higher mortality rates.

Previous research supports the new study´s assertion that human activity plays a major role in the rise of these diseases. A 2008 study published in Nature found that the use of the herbicide atrazine translated to the abundance of larval trematodes in the declining populations of the northern leopard frog. In augmenting snail intermediate hosts and suppressing amphibian immunity, atrazine caused the increased exposure and susceptibility to the flatworms.

To cope with the stresses placed on them by humans, pathogens, and climate change, some amphibians in the latest study increased their production of glucocorticoids.  These steroids boost the creatures´ resilience, but on a sustained basis, an overabundance of the organic compounds can further suppress their immune system.

Finally, the report cited climate change as another driver of increased infection rates. The cycle of warmer winters and night-time temperatures may reduce the amount of pathogen die-offs that would naturally occur in colder regions. Therefore, these regions have become increasingly hospitable to the causes of disease.

In their conclusion, the researchers noted that the forces conspiring against amphibians are complex and interlinked. For example, the effects of climate change may cause some amphibian pathogens to increase in prevalence and severity, while others might decline.

They added that understanding the driving forces behind these changes will be important not only to address amphibian declines but could also be applied to similar problems in other animal populations, including humans.


Source: Brett Smith for redOrbit.com - Your Universe Online



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