A Field Study of Fertilization and Embryonic Development in the Common Frog (Rana temporaria) with Particular Reference to Acidity and Temperature

Abstract

(1) Fertilization and embryonic development in Rana temporaria (L.) were studied in two field-based experiments. (2) Thirty-six ponds in northern England were used, ranging in altitude from 183 m to 617 m. Several of these ponds were cold, acidic and had high concentrations of toxic metal ions. (3) Inorganic monomeric aluminium concentration was the principal factor reducing fertilization success. (4) Exposure to a high zinc concentration, early in development, subsequently increased the number of abnormal embryos. (5) Low minimum pond temperature was the principal factor increasing embryonic mortality. This factor may be less significant in warmer breeding seasons. Most dead eggs were at the mid to late cleavage or early gastrula stage. (6) Most embryonic abnormalities were associated with the incomplete absorption of the yolk plug during gastrulation. Inorganic monomeric aluminium concentration was the principal factor associated with this type of abnormality. (7) Saprolegnia sp. infection of frog eggs was greatest in cold, acidic ponds, with low calcium concentrations.