THE EVOLUTION OF MATING STRATEGIES IN BULLFROGS, RANA CATESBEIANA.

Abstract

Mating system theory is undergoing considerable revision and elaboration (for example: Fisher, 1958; Brown, 1964; Williams, 1966, 1975; Orians, 1969; Cody, 1971; Trivers, 1972; Alexander, 1975; Emlen and Oring, 1977; Alexander and Borgia, 1978). These theories are based upon Darwin's (1871) concept of how natural selection acts within and between the sexes: intrasexual selection, sexual competition between members of the same sex for mates, and intersexual selection, in which one sex is the selective agent for the other. Unfortunately, adequate data to test these theories are lacking for most organisms (but see Bateman, 1948; Savage, 1961; LeBoeuf, 1974; Chagnon, 1974; Jenni, 1974). In this paper, I present necessary data on how mating success varies within and between the sexes to test existing theories of sexual selection for one species, the bullfrog, Rana catesbeiana, and I extend current theoretical considerations to include how age should influence alternative male mating strategies. Anurans are excellent animals to test theoretical predictions of sexual selection: since males fertilize eggs externally, there is no doubt about male parentage and, thus, relative male mating success. Such high confidence of paternity is lacking for most species with internal fertilization. Additional attributes of bullfrogs which make a study technically possible include (a) a tendency for chorusing males to form relatively dense aggregations thus facili-