Litter leachates inhibit growth of a common amphibian pathogen, Batrachochytrium dendrobatidis
The recent global decline in amphibian populations is partially attributed to a rise in parasitic infections, particularly from the chytrid fungus, Batrachochytrium dendrobatidis (Bd). Despite the apparent wide-spread nature of this pathogen, we have a poor understanding of the environmental factors that might limit its distribution. One possible limitation to the growth of Bd might stem from aquatic inputs of terrestrial plant litter, which leach many chemicals into the water and can dramatically change water chemistry. In particular, the leaching of phenolic acids is suggested to inhibit microbial growth and it is reasonable to expect it will also inhibit the sporulation of Bd. In this study, we hypothesize that the chemical variation among leachates of different plant litter species will generate variation in sporulation rates, and we predict that spore counts will be negatively correlated with phenolic acid concentrations. We also predicted that spore counts will decrease with increasing leachate concentrations.
To test this hypothesis, we grew cultures of Bd in three different dilutions of leachates from 12 tree and grass litter species common to North American temperate forests and wetlands. After allowing cultures to grow for four weeks, we found treatment differences ranging two orders of magnitude. Several litter species (e.g., Acer rubrum, Salix nigra) strongly inhibited sporulation whereas other species (e.g,. Populus deltoides) generated no reduction in sporulation relative to no-leachate controls. Spore counts were related to phenolic concentrations, but only at the lowest dilution. Our results implicate terrestrial plant diversity as a strong determinant of a common aquatic parasite and further suggest that litter chemistry might provide a natural infection barrier for host species.