The Influence of Male‐Defended Oviposition Sites on Early Embryo Mortality in Bullfrogs

Field studies were conducted on factor affecting embryo mortality in bullfrogs, Rana catesbeiana, in 1975 and 1976 at the E. S. George Reserve of the University of Michigan. Larger ♀ produced significantly larger clutches than smaller ♀ (6000 to >20,000). Older ♀ produced 2 clutches each year with 2nd clutches containing significantly fewer eggs than 1st clutches. Egg size appeared to be unrelated to ♀ size; however, 2nd clutches contained significantly smaller eggs than initial clutches for all ♀♀. Embryo mortality depended on ♀ choice of oviposition sites. Such sites were controlled by territorial ♂♂. Larger ♂ ♂ controlled oviposition sites that had significantly lower embryo mortality than the sites of smaller ♂ ♂. Sources of embryo mortality included developmental abnormalities and predation. Choice of oviposition sites included: (a) advance of areas with high water temperatures (>32 degrees C) that result in increased developmental abnormalities and (b) preference for areas that increase embryo survival by increasing developmental rate and/or decreasing efficiency of predation on embryos by the leech. Macrobdella decora.