Climate Change has Deadly Effect on Amphibian World

According to a latest discovery that is being published in the Monday's Journal Nature Climate Change, climate change makes frogs more susceptible to deadly diseases.  

Experiments carried out by the researchers indicate that frogs are at a higher risk of a disease that spreads due to the presence of fungus Batrachochytrium dendrobatidis (Bd) if the temperatures alter to great extent. When temperatures vary unpredictably, frogs succumb faster to chytridiomycosis, which is killing amphibians around the world.

Chytridiomycosis affects frogs and their amphibian relatives like salamanders and the worm-like caecilians that has caused to a number of species extinctions.

"I'm not convinced that the effect we've discovered could be considered responsible for declines or extinctions in the ways way that the spread of Bd can be considered responsible," said Thomas Raffel, lead scientist on the new research. "It might be, however, that climate change has sped up the decline or extinction after the parasite arrived."

Several experiments were carried out for years by scientists to find whether Bd is more active in warm or cold temperatures. This new study focuses on what actually happens when chytrid fungus is actually on a vulnerable frog for which the scientists focused on changing temperature rather than temperature itself.

The scientists exposed Cuban treefrogs in 80 laboratory incubators to varying temperatures and infected with Bd. In one experiment, frogs kept at a temperature of 25 degrees Celsius (77F) for four weeks suffered far more infections when they were shifted to incubators at 15C (59F) and exposed to the fungus than frogs already used to living at 15C.

"If you shift the temperature a frog is more susceptible to infection than a frog that is already adapted to that temperature," Raffel said.

In another test, frogs that were exposed to predictable daily temperature variations between 15 and 25 Celsius, typical of shifts from night to day, were much better at resisting the fungus.

On doing so the researchers noticed that fungus did better in cooler conditions and when temperature changes were regular. But when it was frogs the patterns reversed, they noticed the fungus grew faster under unfavorable and unpredicted temperature change.

Based on factors including their size, life expectancy and factors such as their metabolisms, the scientists said frogs probably took 10 times as long as fungus to get used to unexpected temperature changes, a process known as acclimation.

But Raffel suggested it was hard as of now to project what this meant for amphibians and the chytrid threat.

"There's a lot of observational evidence that climate change is leading to increased variability and unpredictability of temperature and precipitation, and it's entirely possible that the kind of effects we observed could become more important in the future," he said. "But I think it's really difficult to make extrapolations - partly because work needs to be done with additional species, and also because we haven't done the experiments yet that would allow us to make predictive models in a quantitative way."

Raffel concluded saying, "We're highlighting this glaring hole in our understanding of how climate change affects biodiversity,"