It is important to recognize that the display of the maladaptive behavior affects not only the isolated animal but can also have unintended affects on the dam (in studies of infant-parent bonds), the potential offspring of the animal, and the conspecifics that may be forced into the animal’s social group. In some species, such as nonhuman primates, dams also show a response to separation from their infants. Their behavioral and physiologic reactions appear to be similar to those of the infant, although less persistent and intense (NRC, 1992), and steps should be taken to minimize this distress if it is an unintended byproduct of the experiment.
The offspring of animals in social disruption experiments may also be impacted by the maladaptive behavior of its dam. For example, female rhesus macaques that are isolate-reared can be neglectful or abusive of their infants (Suomi, 1978). In that situation, it may be appropriate to provide additional support to the offspring or protect it from injury.
In some cases, social disruption causes aggression toward conspecifics. For example, social restriction of male mice will lead to intermale fighting (Brain, 1975). Similar findings have been observed in gerbils, hamsters, and rats (Karim and Arslan, 2000; Payne, 1973; Wechkin and Breuer, 1974). Isolation-reared rhesus monkeys are hyperaggressive and do not develop normal social relationships with other monkeys (Anderson and Mason, 1974; Mason, 1961); this aggression can be directed to other animals or be self-directed (Gluck et al., 1973). Steps should be taken to prevent injury in these cases. For instance in nonhuman primates, this may require housing the aggressive animal separately (AWR 3.81(a)(1)) or the use of screen barriers within cages to permit side-by-side contact, but prevent agonistic encounters.
Several common models are used in studies whose primary intent is to induce aggression or predatory behavior (Mench and Shea-Moore, 1995):
Isolation-induced aggression. This involves isolating a male mouse or rat for several weeks and then staging a brief encounter (usually 5–10 minutes) with an unfamiliar group-housed male. Encounters may be staged either in the isolate’s cage or in a neutral arena. If drugs are administered, they may be administered either to the isolate or to both animals. Because cues from the introduced animal can affect the outcome of the encounter, introduced mice are sometimes rendered anosmic before testing to make them less responsive to social stimulation (Stowers et al., 2002).
Naturalistic paradigms. These studies aggression by placing animals in circumstances that approximate the situations that they might encounter in the wild, where they have to compete for resources, defend territories, or integrate into new social groups. Examples are introducing an ‘intruder” animal into the cage or enclosure of a group of resident animals (Blanchard et al.,