Defensive behaviors in wild and laboratory (Swiss) mice: the mouse defense test battery

The development of laboratory rodent models for elicitation and measurement of a range of defensive behaviors raises the question of the relationship between defense in these animals and those of their wild congeners. To evaluate this relationship for mice, defensive responses to an anesthetized rat were compared for fourth-generation laboratory-bred wild mice and Swiss CD-1 (Swiss-Webster derived) laboratory mice in a Mouse Defense Test Battery. Wild mice showed enhanced levels of both freezing and flight, fleeing from distant approach of the predator in several situations and fleeing more quickly than the Swiss mice. However, Swiss mice did flee upon contact with the rat and also showed levels of several other defensive behaviors (risk assessment, defensive threat, and attack) that were often reliably higher than those of the wild mice. However, when wild mice were prevented from fleeing, their levels of defensive threat and attack were as high as, or at very short prey-predator distances higher than, those of the Swiss mice. These findings suggest that flight and freezing are the major defensive behaviors reduced in Swiss mice and that these reductions allow the appearance of higher levels of additional defensive behaviors in the laboratory animals. However, although Swiss mice do show lower levels of flight and freezing, their patterns of defensive behavior are sufficiently similar to those of wild mice that they provide adequate subjects for research on the biologic bases of defensive behavior. A final experiment indicated that when wild mice are familiarized with a chamber providing a place of concealment, they flee directly to this chamber on presentation of a rat, indicating that flight is a targeted response and not simply an abrupt increase in forward locomotion. Over 10 rat presentation trials with a blocked chamber entrance, however, this response declines.