Consistent Individual Differences in Standard Exploration Tasks in the Black Rat (Rattus rattus)

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In a fluctuating environment, the optimal level of exploratory behavior depends on the proportion of current risks and benefits. The exploratory behavior is, therefore, often subjected to heterogenous selection. In populations of commensal rodents living in close proximity of humans, this pressure is further increased by pest management. We hypothesize that the black rat (Rattus rattus) responds to this pressure by either high behavioral flexibility or by development of personality types. The aim of this study was to analyze exploratory behavior and boldness of wild black rats and its changes over time to determine whether exploratory behavior is a personality trait in black rats. Studies on animals with unreduced variability are necessary for determination of normal range of behaviors. The behavior in the open field and hole board tests yielded 1 multivariate variable representing exploratory behavior and 1 representing boldness. The hole board test additionally provided an axis representing exploratory behavior. Exploratory behavior showed moderate to high repeatability, even though we observed a considerable effect of habituation. Exploratory behavior was also strongly correlated across contexts; therefore, our results suggest that the black rat responds to heterogenous selection pressure by developing personality types. We also found a strong effect of litter identity on some aspects of the exploratory behavior. Boldness was less repeatable, which we interpret as high behavioral flexibility in this behavioral trait. In concordance with our hypothesis, the personality types in exploratory behavior, but not in boldness, are possibly maintained by heterogenous selection pressure created by human pest management.

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