© 1984 by The Society for Integrative and Comparative Biology
Alternative Mating Behaviors of Young Male Bullfrogs1
Department of Biological Sciences, Purdue University West Lafayette, Indiana 47907
Yearling male bullfrogs often attempt to intercept and mate with females attracted to older, larger males (male parasitism) instead of defending a territory and attracting their own mates. Mating behaviors like male parasitism are thought to occur only when individuals suffer some strong disadvantage in using the behaviors that are more typical of their species. In this paper, I consider the relative benefits and costs of territoriality vs male parasitism for yearling males. Yearlings employing male parasitism are only occasionally successful at mating, and in years of reduced male-male competition, they produce significantly fewer young than territorial males of their age. Yearling males that vary in the degree to which they employ territorial behaviors instead of male parasitism do not differ measurably in growth rate or chances of mortality; however, indirect information suggests that territoriality should entail a greater chance of mortality. A computer simulation based solely on observed demographic parameters predicts that yearling males should be territorial whenever they can compete as effectively as two-year-old males. This condition appears to provide little restriction on the breeding tactics of yearling males; however, data on male-male aggressive encounters show that the size differences between one-year-old and two-year-old males are usually sufficient to preclude yearling males from competing successfully. Thus, the observed behavioral plasticity of yearling males may be best interpreted as a means of adjusting their behavioral tactics to levels of male-male competition that can vary within and between breeding seasons.