The Effects of Exposure to Mild Acidic Conditions on Adult Frogs (Rana pipiens and Rana clamitans): Mortality Rates and pH Preferences

In this study we report mortality rates of adults of Rana pipiens to mild acid exposure and pH preferences for R. pipiens and R. clamitans. We exposed adult R. pipiens to mildly acidic conditions for a ten day period under controlled laboratory conditions. Frogs exposed to citrate buffer at pH 5.5 for 10 d exhibited 72% mortality as compared with 3.5% mortality in the control group held at pH 7.0. Furthermore, within the pH 5.5 group there was a difference in acid sensitivity based on season. All of the frogs that had recently emerged from hibernation died within the first four days of exposure to pH 5.5, whereas frogs that were post breeding suffered 58% mortality throughout the 10 d of the experiment. This study also examined the pH preferences of adult frogs. Individuals of R. pipiens (N = 24) and R. clamitans (N = 12) were placed in a six-compartment experimental chamber filled with three different pH solutions buffered to pH 4.0, 5.5, and 7.0. Frogs of both species preferred the more neutral pHs. Our results suggest that adults of R. pipiens are sensitive to mildly acidic conditions, especially when emerging from hibernation, and that adults of both R. pipiens and R. clamitans can discriminate between acidic and neutral pH environments.