Body size predicts the selection of defensive behavioral strategies

Survival depends on the ability to respond appropriately to threats, yet the selection of defensive behaviors varies among individuals with distinct biological traits. Using an active avoidance paradigm in Long-Evans rats, we found that the choice between proactive and reactive defensive strategies was associated primarily with body size, and less associated with sex or age. Smaller animals, regardless of sex or age, more readily acquired active avoidance responses, whereas larger animals predominantly exhibited freezing behavior in response to threat. These differences could not be explained by variations in general locomotor activity or sensitivity to innately aversive stimuli. Our findings suggest that animals integrate intrinsic bodily traits, such as body size, into their assessment of threat, thereby influencing the selection of defensive behavioral strategies.