THE EFFECTS OF LOW PH AND ALUMINUM ON BREEDING SUCCESS IN THE FROG RANA-TEMPORARIA

The effects of low pH on fertilization and embryonic development in Rana temporaria (L.) were studied in the laboratory and field. In the field, fertilization success was reduced principally by high concentrations of inorganic monomeric aluminum, while embryonic mortality was caused mainly by low water temperatures. Most dead eggs were at the mid to late cleavage or early gastrula stage. In the laboratory, embryonic survival decreased with increasing inorganic monomeric aluminum concentration at pH 4.5. High concentrations of inorganic monomeric aluminum also increased the number of embryos which died in the early stages of development, and increased the proportion of embryos which remained constricted within the perivitelline membrane and failed to hatch. The body length of surviving larvae was decreased by both increasing aluminum concentrations and low pH. In acidic water, the body length of larvae from parents caught in an acidic pond in Northumberland was decreased less than that of larvae from parents caught in a circumneutral pond in Nottinghamshire. In both the laboratory and the field, most embryonic abnormalities were associated with the incomplete absorption of the yolk-plug during gastrulation. High inorganic monomeric aluminum concentration was the principal factor associated with this type of abnormality, although in the laboratory this abnormality also occurred at pH 4.5 in the absence of aluminum. Liming of acidic ponds can increase fertilization success and the survival of R. temporaria embryos.