USF Study: Frogs Getting Sick from Climate Change

Project confirms cause-effect relationship between temperature fluctuations and disease-induced frog mortality.


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.


Vickie Chachere can be reached at 813-974-6251.