Delayed Effects of Nutrients in the Larval Environment on Cope's Gray Treefrogs (Hyla chrysoscelis) Exposed to Batrachochytrium dendrobatidis
Excess nutrient runoff can profoundly alter aquatic habitats and has been associated with changes in host–pathogen interactions. Floating macrophyte mats have been suggested as a management strategy to improve water quality for aquatic communities and, thus, may have the potential to protect hosts from some disease outbreaks. We assessed the impact of ammonium nitrate and sodium phosphate addition in the presence or absence of floating macrophyte mats (blue flag iris [Iris versicolor] and ice dance sedge [Carex morrowii]) on Cope's Gray Treefrog (Hyla chrysoscelis) metamorphosis to examine whether macrophyte management treatments improve outcomes for amphibians. At metamorphosis, we infected individuals with the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), to assess whether larval treatments resulted in differential susceptibility to this pathogen. We found that nutrient addition significantly increased time to metamorphosis without affecting mass at metamorphosis or survival. Additionally, Bd exposure decreased mass of juvenile treefrogs, regardless of earlier larval environment or condition at metamorphosis. Macrophyte addition had no direct impact on larval anurans, but the aquatic community was altered via fluctuations in aquatic nutrient concentrations. Overall, our study suggests that nutrient exposure and Bd infection individually affect anurans, and larval exposure to nutrients may have latent effects on metamorphosed anurans that could affect future fitness.ABSTRACT
Image of our floating macrophyte mats including two ice dance sedge and one blue flag iris plant for the macrophyte treatment in our mesocosms.
Anuran time to metamorphosis (A), mass at metamorphosis (B), and survival to metamorphosis (C) across nutrient and macrophyte treatments. Time to metamorphosis was significantly higher in ponds treated with nutrients. Error bars represent the standard error.
Changes in anuran terrestrial mass over time for metamorphs exposed to nutrients in the larval environment and chytrid fungus postmetamorphosis. Negative dates indicate weigh dates prior to Bd exposure (terrestrial experimental day 0). Larval nutrient exposure resulted in significantly larger individuals over time, while exposure to chytrid fungus resulted in significantly smaller individuals over time. Error bars represent the standard error.
Measured nutrients in mesocosms over time by macrophyte and nutrient treatments. Nutrient addition significantly increased total nitrogen over time (A), while macrophyte addition significantly increased nitrogen early in the experiment and decreased nitrogen later in the experiment (B). Total phosphorus decreased significantly over time, but nutrient additions had no effect (C). Macrophytes significantly increased total phosphorus (D). Phosphate changed over time in response to nutrients (E) and was significantly higher in ponds with the macrophyte treatment (F). All nutrients were log transformed to meet normality assumptions. Error bars represent the standard error.
Chlorophyll a (a measure of phytoplankton abundance) significantly varied over time by macrophyte treatment (A) and nutrient treatment (B). Chlorophyll a was log transformed to meet normality assumptions. Error bars represent the standard error.
Contributor Notes
These authors contributed equally to this work.
