Impacts of chytrid and contaminants on South Dakota amphibians

Background/Question/Methods
The amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) is known to be causing population declines in several areas of the world, but nothing is known regarding its presence in South Dakota.  These populations in particular are also impacted by land use changes, with agricultural interests severely modifying and removing native habitat.  As amphibians are also exposed to runoff water from these sites, they are susceptible to contamination of several types. Very little field and only a small amount of laboratory research has examined the role of contaminants in increasing disease susceptibility in amphibians.  To examine the question of Bd prevalence in the state of South Dakota, we conducted surveys across several regions of the state to determine to prevalence and extent of Bd presence.  We also conducted an intensive field study at 20 sites along the Missouri River in Southeast South Dakota to examine the presence of both chytrid and contaminants and any potential interactions between the two.  Using the pesticides found at the sites, we then conducted laboratory experiments to examine more directly the potential impacts of pollutants on amphibians.

Results/Conclusions
We detected Bd in five different amphibian species in three separate regions of the state at an overall prevalence of 6%, although a single site exhibited 64/68 positives.  In 15/20 focal study sites we detected atrazine, with five also containing acetochlor and metalochlor.  Bd was also present at several of these sites, but no significant field pattern was detected between contaminant and Bd presence.  Despite this, we did see relevance of site type in the laboratory. Leopard frog larvae collected in the wild from high agricultural impact sites demonstrated decreased survival no matter what the treatment exposure.  In addition to this, we also found sub-lethal effects (reduced SVL and mass) in these tadpoles occurring at low (0.5 µg/L) and medium (5µg/L) concentrations of atrazine.  Bd exposure showed no impact on tadpoles on its own or in conjuction with atrazine exposure.  We hope to conduct future experiments on metamorphs from these differing sites to better determine the potential for increased susceptibility to Bd in particular species.  From these studies, we can see that further research investigating the interactions between environmentally relevant pesticide levels and pathogens such as Bd can be critical in understanding potential impacts to amphibians in an agricultural landscape.