Spatial and temporal patterns of Batrachochytrium dendrobatidis occupancy in amphibian habitats

Background/Question/Methods

The chytrid fungus Batrachochytrium dendrobatidis (Bd) is an aquatic pathogen to amphibians implicated as one of the causal agents for global amphibian declines across a spectrum of habitats ranging from heavily degraded to intact wilderness. Bd was first described in 1999, and has been detected in museum specimens dating back to at least 1902. Bd research has focused primarily on the ecology of the pathogen in infected amphibians. Our research seeks to describe Bd ecology in the aquatic environment outside of the amphibian host, evaluate spatial and temporal patterns of detection and density, and investigate the relationship between Bd occupancy and potential covariates including water quality. In spring/summer 2007–10, we collected Bd samples by filtering water from amphibian breeding sites at 36 sites in the United States and measured temperature, pH, and specific conductance at a subset (19 sites). We also intensively monitored one site in Oregon, collecting monthly Bd samples and water quality measurements from 2007 to 2011. DNA was extracted from filters and Bd was quantified using qPCR following established methods. Occupancy modeling was performed using the program PRESENCE, we used AIC as a measure of parsimony for model selection.

Results/Conclusions

Bd was detected at 47% of sites sampled (17 of 36 total sites, and 9 of 19 subset with water quality measurements); however, individual site estimates of occupancy ranged from 0.07 to 0.83. Bd occupancy was conditional on pH and detection was conditional on pH and volume filtered. At the intensively monitored site, Bd was detected at least once in every month over 4 years of monitoring. Density reached a peak in spring of every year and a second smaller peak was observed in December in two of the four years. Our findings contribute to the understanding of the ecology of Bd in the aquatic environment, which will be critical for amphibian conservation. The patterns observed at these sites have informed hypotheses we will test across a broader landscape in the next year.