Evolutionary dynamics of frequency-dependent growth strategy in cannibalistic amphibians Authors: Joe Yuichiro Wakano, Yukihiro Kohmatsu and Norio Yamamura Center for Ecological Research, Kyoto University, Kamitanakami Hiranocho, Otsu, Shiga, 520-2113, Japan)

Cannibalistic amphibian larval morphs, being characterized by greater head widths than typical morphs and therefore advantaged by having a larger mouth, provided a basis for the construction of a simple model of cannibalism that describes the growth dynamics of body shape. As the relative head sizes of interacting individuals determine the occurrence of cannibalism, the situation is frequency-dependent. Because natural enemies more often prey upon individuals in more unbalanced body shape, there should exist the optimal growth schedule. Necessary condition for an evolutionarily stable strategy (ESS) is derived analytically and sufficient condition is checked by evolutionary simulation. When the probability of cannibalism is low, an ESS exists. In such cases, the body shape is more balanced (less adaptive to cannibalism) when predation pressure is higher and population density is lower. When the probability of cannibalism is high, there is no ESS. For such cases, a computer simulation of the evolutionary dynamics revealed that the dominant growth strategy changes cyclically. Development of a more detailed model of individual-based population dynamics showed that the qualitative results of the simple model held for the individual-based model. Accompanied by cyclic evolution, the number of surviving individuals at metamorphosis oscillated. The frequency-dependent models suggested that the evolutionary dynamics of cannibalism change drastically depending upon environmental conditions.