Insensitivity to road salt: an advantage for the American bullfrog?

The health of freshwater ecosystems is negatively affected by a multitude of pollutants. In northern latitudes, road deicing agents enter nearby ponds and waterways elevating chloride concentrations in winter and spring. Few studies have examined how amphibians respond to road salt contamination and no study has focused on the response of an invasive amphibian. We examined the effects of NaCl, the most commonly used deicing agent, on the embryos and tadpoles of the American bullfrog, Lithobates catesbeianus , a species that is invasive in many regions around the world. In the first experiment, we exposed L. catesbeianus embryos to ecologically relevant levels of chloride for 60 days. The second experiment examined the indirect consequences of chloride contamination by exposing L. catesbeianus tadpoles to dragonfly larvae. Lithobates catesbeianus did not experience reduced survival, growth, or ability to evade predation in elevated chloride concentrations compared to controls. The lack of a response by L. catesbeianus suggests that its population growth will not be negatively impacted by road salt contamination. This result may be good news for L. catesbeianus , but raises concern for sympatric amphibians that have to contend with negative impacts of both chloride contamination and non-native L. catesbeianus .