Impacts of ammonium nitrate on survival of tadpoles of the common skittering frog (<em>Euphlyctis cyanophlyctis</em>)

Abstract

Amphibians are sensitive to agricultural chemicals such as pesticides and fertilizers. Data on responses of anuran species commonly found in agricultural areas of Pakistan to chemical pollution are lacking. We studied the effects of ammonium nitrate on survival of tadpoles of common skittering frog (Euphlyctis cyanophlyctis). Tadpoles were collected from seasonal shallow water ponds formed during rainy season in the vicinities of Rawalpindi and Islamabad cities. Tadpoles were treated with ammonium nitrate at either 62.5, 125, 250, 500 or 1000 mg nitrate / l, and compared with a control group. Individual survival was significantly affected by increased ammonium nitrate treatments (P < 0.05), with survival rates after 18 days of exposure ranging from 83% at 62.5 mg NO₃^- / l to complete mortality at the highest ammonium nitrate concentration. The logistic regression model with individual survival as a binomial outcome variable and fertilizer concentration as independent variable explained 87% of the variance in survivorship (Nagelkerke R²), and correctly classified 94.0% of the cases (χ² = 259, 5 d.f., P < 0.0005). Our lab-based findings suggest that ammonium nitrate at high concentrations may affect anuran species of Pakistan in croplands with extensive nitrogen-based fertilizer use.