How Synergies Influence the Response of Amphibians to Disease

In my presentation I will review how recent research has helped us understand the role of environmental factors on the dynamics of infections diseases, particularly chytridiomycosis, among amphibians at risk.  Chytridiomycosis is a skin disease caused by a fungus Batrachochytrium dendrobatidis (Bd) that has been associated to amphibian declines all over the world. We hypothesized that temperature and precipitation would influence the amphibian-Bd interaction because it interferes with the physiology of both the pathogen and the hosts, but we did not know how.   Since then, we have found that Bd grows best at temperatures between 17-25 °C and that it reproduces via flagellated spores that disperse through water. Amphibians require moist skin for gas exchange and proper electrolyte balance, and many need water bodies for reproduction. Thus, climatic factors can significantly affect Bd virulence and host susceptibility. 

Scientific advances and international collaborations like the Global Amphibian Assessment (GAA), and the Research Network for Neotropical Amphibians (RANA), helped identify amphibians at risk and prioritize research goals. For example, amphibian population monitoring methods were standardized and coupled with Bd diagnosis via genetic molecular techniques. Worldwide predictive models of Bd distribution were developed from algorithms informed from satellite climate data and precise instruments that measure temperature and precipitation in microhabitats. 

At a global scale, results revealed that Bd prevalence is correlated with low temperatures and high humidity, and some areas like desserts and the Amazon basin have low suitability for Bd.  At a smaller scale this interaction varies considerably with geographic site, and the ecology, physiology, immunity, behavior and life history traits of the species involved.  In places with high suitability for Bd, amphibians that move to warmer spots decrease the probability of Bd infection, and for species with a wider distributions, warmer and drier areas serve as refuges from Bd.  In diverse tropical amphibian communities the rainy season increases Bd infection probability due to higher disease transmission during reproduction, and availability of water for spore dispersal. In contrast, for direct-development frogs that do not go to water to reproduce, drought increases infection probability by encouraging frogs to clump at humid sites where Bd is also more likely to occur.

Thus, climate change, and particularly climate warming can have different effects on amphibian-chytrid dynamics depending on many factors intrinsic to the locality and the community of hosts involved. At present we have a good idea of how climatic factors contribute to form “Hot spots” for Bd, but we need to investigate how other physical, chemical, and biotic characteristics of the environments affect disease outcome. Education can develop values and promote public awareness that may lead to necessary funding for interdisciplinary teams of scientists to lead this research.