What Stops Mass Extinctions?

“Because we have pathogen and host samples from before, during and after the epidemic, we can ask whether some frogs survived because the pathogen grew weaker through time, or because the frogs’ immune systems or resistance increased through time,” said Jamie Voyles, disease ecologist at the University of Nevada, Reno, and first author of the paper.

The authors tracked changes in amphibian species numbers and communities, infection patterns, host resistance and pathogen virulence for several decades hoping to see evidence of a weaker pathogen and/or of host resistance. The disease-causing fungus, Batrachochytrium dendrobatidis, appeared in El Cope, Panama, in 2004, in El Valle in 2006 and in Campana National Park in 2007. Between five and 13 years after the epidemic, the authors saw evidence of some recovery in nine species, but the fungus was still present. However, not all frog species rebounded, some species are still missing.

There was no evidence that the pathogen grew more slowly, responded differently to skin secretions from the frogs or became less virulent.

“The Panama Amphibian Rescue and Conservation Project collected healthy frogs before the outbreak,” Ibañez said. “We learned to breed them in captivity and are now releasing Atelopus varius in areas where the epidemic has passed, so it is extremely important for us to realize that the defenses of these frogs may be weaker than the defenses of frogs that survived the epidemic in the wild. Captive breeding programs must consider breeding and releasing frogs with stronger defenses, and testing their skin secretions against the fungus is one useful tool to see which frogs are more resistant.”

As in other pathogens that infect multiple species, the chytrid fungus poses a threat to amphibians, the cytrid fungus poses a threat to amphibians, increasing the likelihood of extinction of some species. It is vital to understand how disease transitions work–from outbreak, to epidemic, to coexistence–and our results have implications for a skyrocketing human population facing emerging diseases with the potential to cause global pandemics,” said Ibañez.

Contacts and sources:
Beth King
The Smithsonian Tropical Research Institute

Citation:  Voyles J., Woodhams, D.C., Saenz, V et al. 2018. Shifts in disease dynamics in a tropical amphibian assemblage are not due to pathogen attenuation. Science. 10.1126/science.aao4806

Author affiliations include: the Smithsonian Tropical Research Institute; the University of Nevada, Reno; the University of Pittsburgh; the University of California, Berkeley; the New Mexico Institute of Mining and Technology; the Arizona Game and Fish Department; Vanderbilt University; Sistema Nacional de Investigación, Panama; La Mica Biological Station and the Fundación Centro de Conservación de Anfibios, Panama.