Toxic effects of a combined exposure to nitrate and the fungus Batrachochytrium dendrobatidis on the African Clawed Frog, Xenopus laevis
The purpose of this study was to examine the synergistic effects of Bactrachochytrium dendrobatidis (chytrid fungus) and sub-lethal nitrate concentrations on fitness response of the African Clawed Frog, Xenopus laevis. The concern is that the increases in environmentally accelerated anthropogenic influenced nitrogen cycling has stressed otherwise healthy amphibians and, when introduced with B. dendrobatidis, the amphibians are less able to mount an appropriate immune response. The purpose of the experiment to determine if fitness cues normally unseen with infected Xenopus laevis frogs and tadpoles will be exacerbated when influenced with environmentally relevant increased nitrate levels. Conversely, our null hypothesis was no change in fitness when subjected to both B. dendrobatidis and nitrate. The use of this species allowed researchers to test changes that occurred without concern of killing native, naïve species further, thus allowing us to study stressors rather than the outcome of the disease in naïve species (i.e. death). Results indicate tadpoles exposed to high nitrate concentrations experience increased mortality, clutch variability, differences in growth when exposed to chytrid, and increased weight at metamorphosis was uncoupled from time to metamorphosis. Post-metamorphic observations indicate clutch variability, body weight affected by nitrate, and chytrid infection after metamorphosis. Chytrid infection before metamorphosis had no impact on growth or development in post-metamorphic results. Body condition was also significant among nitrate groups and clutches. Regression analyses indicate those exposed to the highest nitrate concentrations experienced a greater increase in weight after metamorphosis experiencing a response reaction similar to other treatment groups.