Consistent individual difference in a behavior is recognized as an important evolutionary force in niche variation and may be a personality trait, an inherent property of the individual. To understand whether aggressiveness is a personality trait, independent of resource holding potential (RHP) and resource value in animal aggression assumed by game theory models, I determined individual variation in aggressiveness by measuringboth positive phonotactic and acoustic responses to the broadcast stimulus repeatedly over the three-week period in males of Gryllus rubens. Factors tested included amplitude levels of the broadcast stimulus, body size, wing dimorphism, and age. The analyses of the generalized linear mixed models revealed that RHP factors such as age, wing dimorphism, and body size, were not significant for both positive phonotactic and acoustic responses. However, there seemed to be more aggressive responses to higher levels of amplitudes. The significant variance-covariance structures of the models indicated that some individuals consistently aggressive or nonagressive during the experimental periods. Because potential factors for resource values were controlled, and because potential RHP factors would not explain variation in aggressive responses, I concluded that aggressiveness is a personality trait that is not characterized by factors that I tested.

• Yikweon Jang(Department of Life Sciences, Ewha University)