Richard Lore

Ultrasounds produced by rats accompany decreases in intraspecific fighting

Male intruder rats were placed individually into the cage of an established resident on 2 occasions separated by a 7–8 day interval. Residents readily attacked intruders and both animals lost weight during the first encounter. In contrast, no serious fighting occurred on the second encounter, and both intruders and residents maintained their body weight during the 24-hr test. Observation of the intruders behavior during the first 30 min of each encounter indicated that defensive-submissive postures represent a response to an attack that only temporarily inhibits aggression whereas the emission of 22 kHz calls by the intruder is associated with a relatively permanent decrease in the resident animals aggressive response.

Play fighting and the development of agonistic behavior in male and female rats

Two longitudinal studies were conducted to quantify the social behaviors exhibited by both male and female Long-Evans rats from the immediate postweaning period until young adulthood. In Experiment 1, male sibling pairs engaged in a high level of play fighting during the early juvenile period but such activity declined to a level significantly lower than that of female and mixed-sex pairs after 54 days of age. In Experiment 2, social exchanges during maturation were examined during the presence and absence of the piloerection response in an effort to distinguish play fighting from agonistic interactions. In male pairs, piloerection was rarely seen before 55–75 days of age but thereafter occurred with increasing frequency especially among dominant males. Furthermore, subordinate males retreated from their dominant partners and remained in an escape chamber for a significant amount of time only during encounters involving the exhibition of piloerection. This finding suggests that piloerection can be useful in identifying play and aggressive interactions. In female and heterosexual pairs, piloerection was observed infrequently during social encounters occurring throughout maturation. In addition, when given the opportunity to escape, females were less likely to retreat from play activity if their partner was another female than a male.

The influence of females upon aggression in domesticated male rats (Rattus norvegicus).

The aggression of adult male Long-Evans rats (Rattus norvegicus), toward males of the same strain, was tested before and after a 1-week period of cohabitation with a pair of intact females, ovariectomized females, or intact males, comparable to the females in size. Only cohabitation with intact females increased the aggression of resident males against unfamiliary male intruders. Female enhancement of aggression does not appear to be caused by sexual frustration of males, or a function of dominance-subordinance relations, per se. Increased aggression may be mediated by elevated testosterone production associated with mating.

Role of vibrissae for depth perception in the rat (Rattus norvegicus)

Summary The role of the vibrissae in the visual cliff performance of rats was investigated. With a moderately low centre-board height, rats with their vibrissae removed show a marked preference for the optically shallow side of the apparatus. In contrast, intact rats do not exhibit a preference for either side. The results indicate that tactual cues are prepotent over visual ones for the rat when conflicting information from both sensory modalities is present.

Intermale and maternal aggression in adult rats tested at different ages.

In Experiment 1, rat colonies consisting of two males and one female were established when the animals were either 100, 200, or 300 days old. All colony members were reared from weaning in small, stable isosexual groups prior to colony formation. Males that were 200 days old engaged in significantly more fighting at colony formation, and, three weeks later, were more likely to wound an intruder during a 24 hr aggression test than either younger or older animals. These findings demonstrate that colony aggression in male rats varies markedly as a function of age when reared under housing conditions that are employed in most laboratories. In Experiment 2, colony females were individually housed after their second pregnancy and their response to a male intruder was evaluated for a 24 hr period after nine days of lactation. Maternal aggression occurred at all ages, indicating that age may be of lesser importance in nest defense of females than intermale conflict. However, maternal aggression was ineffective in preventing the destruction of a high proportion of the litters by intruders in the three maternal age groups.

Empathic learning of a passive-avoidance response in domesticated Rattus norvegicus

Abstract Twelve experimental rats were exposed to demonstrator conspecifics learning to avoid physical contact with a lighted candle in an adjacent compartment. Control rats were also exposed to a lighted candle and a conspecific for comparable periods, but, in the control condition, the demonstrator animal could not contact the flame. Immediately after the exposure period a candle was placed in the observer animals cage. The experimental rats made fewer physical contacts with the candle flame and learned to avoid the candle faster than control animals. These results indicate that domesticated rats learn a passive avoidance response faster after exposure to another animal acquiring the same response. A similar mechanism might account for the wild rats ability to avoid traps and poisoned food.

Observations of the Subterranean Activity of Domesticated and Wild Rats ( Rattus Norvegicus ): A Descriptive Study

The behavior of a small group (varying from five to seven members) of domesticated rats was observed for 11 wk. in an enclosure (171 × 183 cm) which allowed the viewing of animals above and below ground. Comparisons of the development and structure of the burrow system constructed by these animals with burrows built by a group of wild-trapped rats and a pair of devibrissaed laboratory rats revealed no marked differences between the excavation activities of wild and domesticated rats in this context. The excavation, dimensions, and utilization of burrows are described, as well as the social and agonistic interactions of group members in relation to underground habitation.

Differential rearing and free versus forced exploration

Three groups of rats were reared from day 25 to day 65 in either (1) a large free environment cage containing manipulanda, (2) individual restricted environment cages that afforded little sensory or locomotor experience, or (3) in normal cages. Ss were given a brief home cage emergence test designed to evoke “free” exploration. “Forced” exploration was observed by placing each animal in a large cage containing a variety of small objects. FE animals exhibited more exploratory activity in the home cage emergence test but less object exploration in the forced environment.

Avoidance reactions of domestic dogs to unfamiliar male and female humans in a kennel setting

Abstract Most kennel owners and veterinarians prefer women assistants because these animalcare professionals assume that women elicit less avoidance from domestic animals than men. To evaluate this assumption, 10 male and 10 female dogs were given two human-reaction tests to assess their behavior in the presence of an unfamiliar man or woman in a commercial kennel setting. Female dogs showed little reluctance to approach and make contact with the unfamiliar human, regardless of the persons gender. In contrast, male dogs were much less likely to approach and make body contact with the unfamiliar man.

Colony aggression in laboratory rats: a review and some recommendations

The behavioral response of established colonies of domesticated rats to the presence of an unfamiliar intruder of the same species represents one of the most effective procedures yet developed to study aggression in the laboratory. Here, the social, experiential, and environmental variables that influence attack severity are reviewed and several important methodological issues are discussed. Brief exposures of intruders to intact colonies may produce misleading results but long-term test sessions increase the likelihood that intruders will be either killed or severely injured. We describe a simple modification of the colony-intruder procedure whereby intruders can successfully defend themselves during long sessions and thus reduce serious injury. The modified procedure appears to conform more closely to what happens during aggressive encounters in free-living populations of wild rats.