investigating life
Is the most recent dramatic decline of amphibians the result of a novel fungal pathogen, and if so, what can be done about it?
The research to date suggests that amphibian declines are caused by multiple human-instigated factors, including habitat loss and pollution, overharvesting, and even exposure to UV radiation, but that the final fatal blow may be the unintended introduction of the novel chytrid fungal pathogen Batrachochytrium dendrobatidis, or Bd. Population declines and species extinctions of amphibians have occurred at such alarming rates, and in areas that are considered undisturbed, that it can be hard to know how the Bd invasion can be stopped or realistically treated in the wild. Despite these hurdles, scientists are recommending several measures to help control the pathogen’s destructive effects. The first and foremost recommendation is to reduce the volume of amphibian trade and ensure that amphibians transported long distances are required by law to undergo disease testing and quarantine procedures. Second, improvements in diagnostics and knowledge of the disease are needed in both wild and captive settings. Recently, a method using PCR has been developed to definitively identify the fungus in the water and on the skin of potentially infected animals. Third, the risk of spread can be minimized by restricting the movement of captive amphibians, especially to the wild, and by disinfecting footwear and collecting equipment when working in aquatic environments. A variety of strategies that integrate ecological research, socioeconomic interests, and institutional authority will likely be required to save the remaining amphibian species that are susceptible to this highly fatal disease.
Although it is tragic that the harlequin frog (Atelopus varius), once ubiquitous in the mountains of Costa Rica, and the golden frog (Atelopus zeteki), the national symbol of Panama, could disappear so fast, hope still remains. An active area of research involves understanding why some amphibian species, such as the American bullfrog and African clawed frog, are more resistant to Bd while other species are highly susceptible. Some mechanisms that could explain species resistance to the disease are (1) the presence of specific types of bacteria or antimicrobial compounds that discourage Bd growth, (2) inherent genetic resistance to Bd, and (3) certain less virulent strains of Bd. More research will be needed to understand the complexities of the disease. In the meantime, captive breeding programs are under way for both the harlequin frog and golden frog so that they might one day be reintroduced into the Costa Rican and Panamanian nature preserves designed to protect them.