Global Collaborative Responses in Responding to Amphibian Chytridiomycosis
Our initial bias to investigate amphibians in localities with known die-offs (e.g. Panama, California) misled us to propose that we were facing a novel fungal pathogen (Batrachochytrium dendrobatidis, =Bd). Global collaborations uncovered Bd in areas without declines, and identified new strains with diverse genotypes. Bd’s evolutionary history now includes six genetically distinct lineages, an origin that predates any modern amphibian decline, and a recently discovered sister species B. salamandrivorans (Bsal). These findings changed the fundamental knowledge of the amphibian-chytridiomycosis system, because Bd/Bsal distributions vary across continents, as well as their pathogenicity and morphology. Our results have relied on obtaining pure isolates from infected hosts, which is not an easy task under low-level infections. In the future, we expect to develop novel assays that can simultaneously quantify infection load and determine genotypes in a single test.
On the host side, we aim to predict why some species are susceptible while others survive. Using analyses of gene expression, teams found that the lack of immune response—paradoxically—helped frogs survive infection better than frogs that mounted a strong immune defense. Understanding the role of these genes (when do they work or when they are suppressed) can inform captive breeding and reintroduction programs. However, host genetic makeup is only part of the defense strategies. Some naturally occurring skin bacteria have shown antagonistic interactions with Bd, thus can contribute an indirect mechanism of defense for the host.
Taken together, these findings have permitted fast developments to prevent the potential spread of Bsal into naïve salamanders. Global teams employ evolutionary approaches to predict susceptibility to Bsal among salamanders. Now we have informed predictions that will help us prioritize species and areas, but only time will tell if our efforts are adequate.