Low pH affects the fertilization and development of Rana pipiens eggs

Effects of pH on fertilization and the early stages of development of the northern leopard frog, Rana pipiens, were investigated in the laboratory. Sperm motility decreased with decreasing pH below 6.5 in unbuffered solutions acidified with H2SO4 or HNO3, and below 5.5 in buffered solutions acidified with HCl. Motility was lower in the presence of HNO3 than in the presence of H2SO4. No eggs developed at pH 4.8 or below and this failure could not be attributed to low sperm motility. When eggs were inseminated in buffered solutions fertilization, activation, and cleavage decreased with decreasing pH below 6.3, falling to 50% of maximum at about pH 5.8. Fertilizing the eggs at pH 7.3, then transferring them to buffered solutions of lower pH, significantly improved the rate of survival in the first 24 h. Marked decreases in survival occurred at pH 5.8 or below, falling to 50% of maximum at about pH 5.5. By 48 h the embryos at pH 5.5 and 5.8 had stopped developing. Fertilization was more susceptible to low pH than was activation or cleavage. Provided eggs were fertilized, they continued developing at pH 6.0 to 7.5. Below pH 5.8, most fertilized eggs were activated but stopped developing before first cleavage. I concluded that waters more alkaline than pH 6.0 are optimal for fertilization and early development in R. pipiens.