Presence of potential competitors increases boldness behavior over time in a lizard

Background/Question/Methods

Boldness is a widely studied behavior that is frequently correlated with important fitness traits, including body size. This correlation between risk-taking behavior and body size is not always found in laboratory studies, however, leading to the suggestion that the relationship may depend on mortality costs of boldness associated with exposure to predation. In contrast, previous research has demonstrated that competition may be more important than predation in the development of behavior traits. The correlation between boldness and the sociability of individuals as evidenced by some lizard species further suggests that boldness variation may respond to social structure even in the absence of predation. We tested the potential for social influences on boldness behavior in eastern fence lizards using social or asocial housing treatments following a split-clutch design: four siblings were housed together in an enclosure and four other siblings were each housed individually. All lizards were tested for boldness in open field trials 8 days and 8 weeks later to assess boldness behavior over time.

Results/Conclusions

Our results show that lizards from the two housing treatments did not differ in risk-taking behavior at 8 days of age, but by 8 weeks of age the socially-housed lizards were bolder overall. Moreover, there was a significant, positive correlation between body size and boldness behavior at 8 weeks of age among socially-housed lizards but not among those that were housed individually. This correlation may be the result of improved competitive ability, as bold individuals may make better competitors, in turn leading to greater resource acquisition and larger body size. In the absence of competitors, there may be no energetic benefit to boldness, resulting in a lack of boldness variation. Although costs of predation may be important in the development of boldness behavior in the wild, the results of this laboratory study suggest that social grouping may be important in shaping boldness behavior independently of predation pressures.