The Relationship between Egg Size and Acid Tolerance in Rana sylvatica

Abstract

Previous studies have demonstrated that the ability of embryos from the wood frog (Rana sylvatica) to withstand acid conditions is strongly influenced by maternal factors. Here we investigate one possible source of this maternal influence -variation in egg size. Samples of seventeen egg clutches from four populations of wood frogs in Connecticut were measured for ovum volume and capsule thickness. Additional eggs from each clutch were used to assess the acid tolerance of embryos and larvae. Ovum volume was negatively correlated with hatching success at pH 4 and capsule thickness was negatively correlated with hatching success at pH 3.75. The acid tolerance of larvae was not related to ovum size nor to capsule thickness. Ovum volume and capsule thickness varied significantly within populations, but there were no differences in these parameters among the four pop- ulations. The relationship between egg size and acid tolerance was not evident within individual clutches.