USF Study: Frogs Getting Sick from Climate Change
Project confirms cause-effect relationship between temperature fluctuations and disease-induced frog mortality / Proyecto confirma relación causa-efecto entre las fuctuaciones de temperatura y la mortalidad inducida por enfermedad en anfibios
Jason Rohr, USF associate professor of Integrative Biology, works in the field.
By Vickie Chachere
USF News
TAMPA, Fla. (Aug. 13, 2012) – Scientists
studying the rapid decline of the world’s frog populations have
suspected that fluctuating temperatures brought on by climate change
might make frogs vulnerable to disease.
Now, a new study published in the prestigious journal Nature Climate Change
confirms those suspicions, showing in laboratory and field tests that
temperature fluctuations decrease frogs’ resistance to a pathogen
implicated in global amphibian declines.
The
study, conducted by scientists at the University of South Florida and
Oakland University in Michigan, found that unpredictable temperature
shifts temporarily decreased the frogs’ resistance to the deadly
parasite, chytrid fungus. The study is a major step forward in shedding
light on dramatic declines in the world’s frog population; scientists suspect
climate change plays a role, but have been cautious in declaring it a
cause of frog population declines without detailed experiments and more
extensive data.
“In
addition to increasing mean temperatures, global climate change is
increasing climate variability, but few studies have considered how
increased variability in temperature affects disease risk,” said Jason
Rohr, a co-author of the study and an Associate Professor of Integrative
Biology at USF.
“We
hypothesized that temperature shifts associated with climate change
would temporarily benefit parasites because they are smaller and have
faster metabolisms than their ectothermic hosts and thus should
acclimate more quickly to unpredictable temperature shifts.”
To
test this hypothesis, Rohr and colleagues acclimated frogs to either 15
or 25 degrees Celsius in 80 independent incubators, switched half the
frogs at each temperature to the other temperature, and then challenged
the frogs with the chytrid fungus. They
found that frogs experiencing an unpredictable temperature shift, at
either daily or monthly time scales, had greater chytrid fungal loads
and fungal-induced mortality than frogs held at a constant temperature.
The effect was particularly strong when temperatures unpredictably
dropped.
Drops in temperature were also significant predictors of disease-associated frog extinctions in Latin America. Furthermore,
warmer years had larger drops in temperature and more extinctions than
cooler years, providing a mechanistic link between global climate change
and chytrid-related amphibian declines.
“This
study provides an important step in understanding the role that climate
change plays in amphibian declines, but we suspect that its
implications will be even more far-reaching,” Rohr said.
“Temperature
acclimation of host resistance to parasitism is almost certainly a
widespread phenomenon, likely influencing invertebrate vectors of human
diseases,” he added. “Consequently,
climatic variability and predictability might represent
underappreciated links between climate change, disease, and biodiversity
losses.”
Chytrid
fungus kills frogs by causing the thickening of its skin, leading to
electrolyte imbalance and dehydration. It has been implicated in the
decline and extinction of numerous frog species worldwide. Scientists
consider the disease to be one of the biggest threats to amphibian
survival worldwide.
The
study was conducted by Oakland University Assistant Professor Thomas
Raffel, Rohr and USF Department of Integrative Biology postdoctoral
researchers John M. Romansic and Matthew D. Venesky; and PhD candidates
Neal Halstead and Taegan McMahon. The full text can be read here.
