New infectious diseases emerging as a result of climate change may lead to further extinctions of frogs, the bio-indicators of environmental health, recent research has found.

The University of Queensland investigated skin sloughing (shedding) in frogs as an immune defence mechanism, to better understand the role of the skin against infectious disease.

Lead researcher, Dr Rebecca Cramp from UQ’s School of Biological Sciences, said frog and other amphibian populations worldwide are declining due to the emergence of infectious diseases as a result of climate change.

“Environmental temperature and humidity can have a major effect on amphibians as their skin is very permeable and sensitive to dehydration,” Dr Cramp said.

“A number of amphibian species have disappeared or become extinct in the past several years so it is vital to understand the role of the skin as the first line of defense against external causes of disease.”

The researchers studied the Green tree frog (Litoria caerulea) which is highly susceptible to chytridiomycosis, a fungal skin disease contributing to a large number of amphibian deaths across the world.

The fungus which causes chytridiomycosis, as well as other microbes, live on the outermost layer of skin which is periodically shed by frogs.

“We investigated the effect of skin sloughing on the abundance of microbes on the skin, and looked at the effects of temperature and humidity on how often it occurs,” Dr Cramp said.

“Our results showed that when frogs shed their skin, the number of both helpful and harmful microbes remaining is significantly reduced.

“Although it may help the frogs to shed the chytridiomycosis fungus, the loss of protective microbes can allow other pathogens to take hold.”

The green tree frog, Litoria caerulea. Photo credit: Ed Meyer

The researchers also found that environmental temperature, but not humidity, had a marked effect on the frequency of sloughing, with animals in cooler temperatures taking twice as long between sloughings.

Senior author, Professor Craig Franklin from UQ’s School of Biological Sciences, said the study shows that the frequency of skin sloughing may be an important factor in skin-based amphibian diseases.

“The chytridiomycosis fungus is most infective at lower temperatures and the extended period between sloughings can allow it to accumulate to dangerous levels,” he said.

“This may explain why most frog deaths from this disease occur in cooler regions, at higher altitudes and during cooler times of the year.

“The emergence of infectious diseases is predicted to skyrocket as a result of climate change, so understanding the protective role of the skin against external pathogens is essential.”

The research was published in Conservation Physiology on 22 April 2014.

Media: Dr Rebecca Cramp, 0408 076 202, r.cramp@uq.edu.au

Professor Craig Franklin, 0434 602 327, c.franklin@uq.edu.au