Field and Laboratory Studies of Ion Balance and Growth Rates of Ranid Tadpoles Chronically Exposed to Low pH

Abstract

The effect of sublethal, chronic exposure of tadpoles to low environmental pH under natural conditions was investigated by making weekly measurements of various physiological variables. Rana sylvatica tadpoles from a low pH pond (pH 4.05-4.90) had lower body sodium, chloride and water concentrations in comparison with tadpoles from a nearby high pH pond (pH 5.74-6.37). Tadpoles from both ponds placed in the low pH pond also underwent higher sodium efflux than when placed in the high pH pond. These observations parallel similar studies on fish and demonstrate the effects of low environmental pH on larval anuran ionic regulatory mechanisms. Survival times of field-collected R. sylvatica tadpoles placed at pH 3.0 (H2SO4) did not change with age nor were there any differences between tadpoles from high and low pH ponds. However, survival times of laboratory raised R. pipiens tadpoles did increase with age, and animals raised at pH 4.4 grew slower than siblings at pH 5.8.