Developmental and immunological effects of atrazine and selected domestic effluents in the African clawed frog (Xenopus laevis)

Global amphibian populations are currently declining at an alarming rate, suggesting widespread environmental degradation. Although the causes are largely unknown, one major contributing factor is the newly emerged amphibian pathogen, Batrachochytrium dendrobatidis. This chytrid fungus is responsible for several localized mass mortality events, yet the cause of the sudden susceptibility of amphibians to this pathogen is unknown. While antimicrobial peptides secreted from dermal glands are thought to provide the only protection against this newly emerged pathogen, larval growth and growth rate are strongly associated with adult fitness in amphibians. Therefore, chemical-induced alterations in larval development or development of protective bioactive secretions may contribute to declines in global amphibian biodiversity. This study probes a link between xenobiotics and amphibian population declines by studying the impact of common environmental pollutants on critical developmental parameters and a novel component of the innate immune system in the amphibian model, Xenopus laevis. Acute and chronic laboratory exposures designed to represent potential environmental exposure scenarios were conducted. Following exposure to atrazine or locally collected domestic effluents, select developmental parameters were measured as well as the total protein and bioactivity of collected skin secretions. Bioactivity was measured using a growth inhibition assay characterized as an amphibian immunobioassay in our laboratory.; Major findings from this study include the preliminary characterization of a novel amphibian immunobioassay and the discovery that the development of protective antimicrobial peptides can be modulated through chemical exposure. Chronic exposure of X. laevis larvae to agricultural runoff containing ATR or effluents from a municipal landfill and a sewage treatment plant decreased the bioactivity of secretions collected from post-metamorphic animals. Similar effects were observed following acute (24 hour) exposure of juvenile X. laevis to 5 ppm carbaryl. Altered development was also observed following some chronic exposures of larval X. laevis. Larvae exposed to landfill (100%) or sewage treatment plant effluents (50, 100%) were larger in size, while larvae exposed to greater than 10% agricultural runoff were smaller than controls. These findings demonstrate that exposure to environmentally relevant waters can alter parameters critical to amphibian fitness levels, and thereby, may consequently contribute to amphibian population declines.