Behavioral Response of Adult and Larval Wood Frogs (Lithobates sylvaticus) to a Common Road De-Icer, NaCl

Amphibians are highly vulnerable to aquatic pollutants. Due to the permeability of their skin and their aquatic larval stages, pollutants are easily absorbed into the body, which can have adverse effects on performance, survival, and fitness. This has prompted research on how environmental pollutants affect amphibian populations, especially road deicers such as sodium chloride (NaCl). Elevated NaCl can have a negative physiological impact on both adult and larval stages of amphibians, leading to reduced breeding success, morphological abnormalities, and even mortality. However, less is known about the behavioral responses of adults and especially larval amphibians to increased environmental salinity. Earlier studies suggested that adult wood frogs did not show any behavioral responses to varying salinity with short-term (10 min) exposure, while larvae had not been assessed. In this study, the behavioral responses of both adult and larval wood frogs, Lithobates sylvaticus, to increased salinity were studied via salinity choice trials where a control (aged tap water) and a designated salt solution were placed on opposite sides of a binary arena for 3,600 seconds. Adults spent less time in NaCl solutions with increasing salinity. The threshold for response was approximately 0.17 M (slightly hyperosmotic to internal osmotic concentrations). For tadpoles, time spent in salt solutions did not change as salinity increased (to a maximum of 0.25 M NaCl), but these results were confounded by mixing between the control and the salt solutions. There were no behavioral differences in tadpole activity level (number of moves between chambers) as salinity increased. Since increased salinity has been associated with decreased fitness, behavioral avoidance of high salinity and preference for lower saline systems could be advantageous for wood frogs. Adults could potentially select breeding sites with lower solute levels that would be beneficial to egg masses and offspring. However, this study suggests that tadpoles in a high solute habitat may not change their activity level, potentially leading to inability to select microhabitats within a system. In addition, although adult wood frogs did respond to increasing salinity, they did so slower than previously assessed species, potentially making them more susceptible to habitat degradation. This study furthers the understanding of how amphibian populations respond to salinity influxes in the wild and will help to promote better conservation efforts for species vulnerable to salt pollution