Stimulus factors in the isolation-induced aggression of Bobwhite quail and Khaki Campbell ducklings

Two studies examined the relative abilities of conspecific-derived visual and tactile stimulation to modulate the occurrence of isolation-induced aggression in Bobwhite quail and Khaki Campbell ducklings. In Experiment 1, subjects were permitted visual stimulation from conspecifics but were deprived of conspecific tactile stimulation. In both species, these subjects subsequently showed significantly less aggression towards conspecifics than birds that had been deprived of both visual and tactile stimulation from conspecifics. In Experiment 2, one group of subjects was permitted conspecific tactile stimulation but was deprived of conspecific visual stimulation. Again for both species, these subjects subsequently exhibited significantly less aggressive behavior towards conspecifics than did subjects that had been both visually and tactually de-prived. In sum, the present research suggests that both tactile and visual stimulation from a conspecific are individually sufficient to reduce isolation-induced aggression in these precocial buds.     

Predation, aggression, and activity levels in food-deprived sunfish (Lepomis macrochirus and L. gibbosus): motivational interactions

Three experiments investigated the effects of food deprivation on several behavioral categories in two species of sunfish. In Experiment 1, predatory behavior and general activity were observed under five levels of deprivation. For both species, predation measures increased in a similar negatively accelerating manner with increasing deprivation, while activity changed in a more complex fashion. Experiment 2 examined the effects of deprivation on activity in a novel environment and showed that the deprivation effects of Experiment 1 were masked by the response to the new setting. In Experiment 3, measures of aggression toward intruders of each species were recorded from resident fish of both species under three levels of food deprivation. Both species were more aggressive toward conspecifics, and bluegills were more aggressive overall. Aggression was significatly influenced by food deprivation, with the effects dependent on the species making up the pair. Theories of motivational summation, generalized drive, and activity-mediated aggression were unable to explain the differential effects of hunger on the three behavioral categories observed. A dynamic boundary-state model of behavior control was found to predict the motivational interactions observed between distinct behavioral control systems.     

Capuchin monkeys are not prosocial in an instrumental helping task

Comparative research can shed light on the evolutionary roots and cognitive underpinnings of prosocial behavior by revealing not only positive instances of prosocial motivations in other species, but also the boundary conditions of these motivations. To explore factors that may constrain prosocial behavior, we examined whether brown capuchins (Cebus apella), which demonstrate regard for the welfare of conspecifics in other contexts, would behave prosocially in a minimal-cost instrumental helping task. We observed that when given the opportunity to share tokens that allow a conspecific to obtain food from an apparatus, capuchins showed no regard for another individual's welfare. Subjects transferred tokens to an adjacent chamber when the apparatus was present, but did so just as often when the chamber was empty as when there was a recipient present to obtain food. While capuchins are sensitive to others' welfare in some contexts, the current results suggest that they do not spontaneously produce goal-specific helping actions on behalf of a conspecific. The lack of regard for others exhibited in this context provides insights into the factors that may constrain prosocial behavior in capuchins and other primate species.     

Central-place foraging by Rattus norvegicus on a radial maze

We studied central-place foraging in rats (Rattus norvegicus) by placing food items that varied in size and weight at the ends of a 4-arm radial maze. In Experiments 1-3, rats increasingly tended to carry food to the center of the maze as the size of those items increased. Very large food items often were hoarded in the center. Rats consumed food faster on the arms than in the center, and rats traveled faster when carrying food than when not. Blocking arm entrances increased travel time between the center and the arms and decreased food carrying at every item weight except the largest. In Experiments 4-6, important conditions that influence the degree of food-carrying behavior were discovered; these were the intersection of maze arms, the presence of a conspecific, and the use of open vs. closed maze arms.     

Effects of septal-forebrain lesions on maternal aggression and maternal care

Septal-forebrain lesions significantly increased the defensive reactions of lactating Long-Evans rats (n = 13) relative to nonlesioned control females. The lesions greatly enhanced defensive behaviors on a number of standard tests (e.g., responsiveness to humans and anesthetized conspecifics) while abolishing aggression toward intruding male conspecifics. The lesions also produced a striking disruption in maternal behavior as evidenced by absence of nest building, reduced litter weights, failure to retrieve, lick, or nurse pups, and increased cannibalization. While these results cannot be interpreted as indicating that maternal aggression is equivalent to offense, they are congruent with such a view. Certainly they are not supportive of a view that maternal aggression is primarily defensive. The lesion-induced abolition of maternal attack may have resulted from an inhibition of offensive tendencies by heightened defensiveness and/or reduced pup stimulation. There was no evidence that the lesion-induced impairment in maternal behavior resulted from a failure to sequence the individual behavioral acts comprising maternal behavior. Rather, all features of maternal care seemed to be greatly attenuated.     

Lean and mean rats: Some effects of acute changes in the food supply upon territorial aggression

In experiment 1, individually housed rats subjected to short-term food restriction displayed more territorial aggression toward conspecific intruders than controls maintained on a free-feeding diet. In experiment 2, small groups of three adult male rats had access to either a standard laboratory diet or the standard diet plus sucrose. Groups with the sucrose supplement were significantly less aggressive toward intruders than controls. Sucrose availability did not produce appreciable gains in body weight but it did reliably decrease within-colony weight variation. The results suggest the existence of an effective dietary mechanism that enables a social species such as Rattus norvegicus to tolerate each other in dense feeding aggregations when food is abundant. Conversely, when food is limited, social intolerance increases and serves to limit the development of large feeding groups.     

Some characteristics of the aggressive behavior of mice after prolonged Isolation: Intraspecific and interspecific aspects

Experiments on mice have demonstrated changes in the relationships, interdependence and sequence of behavioral items following prolonged isolation. It was found that aggression in isolates was stereotyped and hardly amenable to the control not only by intraspecific but also by interspecific factors. Isolated mice, in contrast to the group-reared animals, spontaneously attacked adult rats. This finding was interpreted as being due to a disruption of behavioral plasticity under circumstances of prolonged isolation from conspecifics.     

Protein deficiency magnifies social influence on the food choices of Norway rats (Rattus norvegicus)

The food choices of protein-deprived juvenile rats were more profoundly affected by interaction with conspecifics than were the food choices of protein-replete juvenile rats. When choosing among four different-flavored, protein-deficient diets, protein-deprived rats ate significantly more of the diet eaten by a conspecific demonstrator than did protein-replete rats. These data suggest that the food choices of the relatively less successful members of a population are most affected by social interaction. Consequently, the mean effect of social interaction on diet selection in a population of Norway rats is likely to be positive.     

Comparing choices and variations in people and rats: Two teaching experiments

Two pairs of experiments enabled students to compare their own operant behaviors with those of rats. The students played computer games for points, and the rats pressed levers for food. The first pair of experiments showed that, under concurrent schedules of reinforcement, relative frequencies of choices between two alternatives increased linearly in rats and people as functions of relative frequencies of reinforcement, with similar biases and undermatching observed in both species. The second pair of experiments showed that behavioral variability was controlled by reinforcers contingent on variability, this again true for both species. These experiments helped demonstrate the relevance of animal operant research to an explanation of human operant behavior.     

Eurasian jays (Garrulus glandarius) conceal caches from onlookers

Animals that cache food risk having their stored food pilfered by conspecifics. Previous research has shown that a number of food-caching species of corvid use strategies that decrease the probability of conspecifics pilfering their caches. In this experiment, we investigated whether Eurasian jays (Garrulus glandarius) would choose between caching behind an opaque and caching behind a transparent barrier whilst being observed by a conspecific. If caching in out-of-sight locations is a strategy to prevent conspecifics from pilfering these caches, then the jays should place a greater proportion of caches behind the opaque barrier when being observed than when caching in private. In accordance with this prediction, jays cached a greater proportion of food behind the opaque barrier when they were observed than when they cached in private. These results suggest that Eurasian jays may opt to cache in out-of-view locations to reduce the likelihood of conspecifics pilfering their caches.     

Androgens and aggressive behavior in primates: A review

This review deals with possible central and peripheral effects of androgens upon primate aggressive behavior. One problem that clouds interpretation of experimental work is that measurements of dominance have often been employed, such as competition tests for food and water. Such measures often do not correlate with those obtained by quantifying aggressive interactions. It should be remembered that very few of the 188 primate species have been studied experimentally and that great behavioral and physiological diversity occurs within the order. Therefore, generalizations about the effects of androgens upon aggressive behavior in primates (including man) should be made with caution. Testosterone has an organizing influence upon the foetal brain of rhesus monkeys and may affect the development of neural mechanisms which govern aggression in males. More data are required on primates, however, since rhesus monkeys show some important differences from rodents as regards the effects of androgen upon sexual differentiation of the hypothalamus. In future, marmosets may provide a suitable model for such studies, because there is evidence that sexual differentiation of brain by androgen occurs postnatally in these monkeys. At puberty, male primates show a variety of behavioral changes and, during adulthood, males of seasonally breeding species may be more aggressive during the mating season, when testosterone levels are maximal. This does not indicate a causative relationship between testosterone and aggressive responses, because castration and androgen treatments have little effect upon aggression in prepubertal or adult males of several primate species. Androgens have pronounced effects on sexual responses in adult male monkeys, but their central effects upon aggression are much less important than among rodents. Elec trical stimulation of hypothalamic pathways has been employed to evoke aggressive behavior in marmosets and rhesus monkeys. In the rhesus, preliminary evidence indicates that such pathways show some sensitivity to androgens. In rodents it is known that these areas are richly supplied with monoaminergic neurons, which play an important role in aggressive behavior. There is little evidence on primates, however, and this remains a crucial topic for future research. Peripheral effects of androgens should also be considered. Many prosimians and New World monkeys use scent-marking behaviors and, in males, androgen-dependent chemical cues may be involved in sexual recognition and territorial behavior. This possibility awaits investigation. Finally, plasma testosterone levels may alter as a function of aggression itself; thus levels decrease if male rhesus monkeys are defeated by conspecifics. This might occur because neural events associated with giving (or receiving) aggression also influence pituitary function and hence alter gonadal testosterone secretion. Theoretically, it is possible that such changes in circulating testosterone might affect aggressive behavior via a feedback action on the brain, but the experimental evidence does not support such a view.     

Defensive behaviors in rats following septal and septal--amygdala lesions

Rats with anterior septal lesions showed a pattern of consistent enhancement of defensive behaviors normally elicited by threatening conspecifics, with no enhancement of attack or general reactivity. Further division of this group indicated that damage to sites anterior and ventral to the septal area, sites previously implicated in the "septal syndrome," produces maximal effect on these behaviors. When amygdala lesions are combined with septal damage this enhanced defensive responding is almost completely eliminated. These results were interpreted as indicating that the septal syndrome represents hyperdefensiveness to conspecific threat stimuli rather than aggression or increased general reactivity, and that amygdaloid mechanisms are also involved in the regulation of conspecific defensive behaviors.     

Studies of Emotional Reactions VI. Cardiac Responses

Wild-strain male house mice were fostered at birth onto conspecifics, deer mice, or domestic Norway rats. In adulthood, their flesh-eating preferences were tested by allowing them to feed from freshly asphyxiated conspecifics and either deer mice or rats. The mice ate significantly more conspecific flesh than contraspecific flesh, except when the flesh offered was that of the contraspecies upon which the mouse had been fostered at birth. The failure of cross-species-fostered mice to discriminate between their own species and their foster species in flesh-preference tests is attributed to their having learned early in life to respond to the foster species in the same way they normally respond to conspecifics, that is, by approaching them, investigating them, and, when finding them dead, feeding upon them.     

Social enrichment improves social recognition memory in male rats

The social environment is thought to have a strong impact on cognitive functions. In the present study, we investigated whether social enrichment could affect rats’ memory ability using the “Different Objects Task (DOT),” in which the levels of memory load could be modulated by changing the number of objects to be remembered. In addition, we applied the DOT to a social discrimination task using unfamiliar conspecific juveniles instead of objects. Animals were housed in one of the three different housing conditions after weaning [postnatal day (PND) 21]: social-separated (1 per cage), standard (3 per cage), or social-enriched (10 per cage) conditions. The object and social recognition tasks were conducted on PND 60. In the sample phase, the rats were allowed to explore a field in which 3, 4, or 5 different, unfamiliar stimuli (conspecific juveniles through a mesh or objects) were presented. In the test phase conducted after a 5-min delay, social-separated rats were able to discriminate the novel conspecific from the familiar ones only under the condition in which three different conspecifics were presented; social-enriched rats managed to recognize the novel conspecific even under the condition of five different conspecifics. On the other hand, in the object recognition task, both social-separated and social-enriched rats were able to discriminate the novel object from the familiar ones under the condition of five different objects. These results suggest that social enrichment can enhance social, but not object, memory span.     

Effects of chlordiazepoxide and cocaine on concurrent food and avoidance-of-timeout schedules.

Five rats were trained on a concurrent schedule in which responses on one lever produced a food pellet on a random-interval 30-s schedule during 10 s of food availability associated with distinctive exteroceptive stimuli. Responses on another lever postponed for 20 s the presentation of a 50-s timeout, during which all stimuli were extinguished and the schedule contingencies on the food lever were suspended. The response rates maintained by the random-interval schedule exceeded those maintained by the avoidance contingency, but both provided a stable baseline to assess the behavioral effects of different drugs. Low doses of cocaine hydrochloride (1 and 3 mg/kg) did not affect food-reinforced responding or avoidance response rates. Intermediate doses (5.6, 10, and 13 mg/kg) produced a dose-dependent decrease in food-maintained and avoidance response rates, and both types of responding were virtually eliminated after administration of the highest doses (17 and 30 mg/kg) of cocaine. Low doses of chlordiazepoxide (1 and 3 mg/kg) increased food-maintained and avoidance response rates, and both rates decreased systematically after 10 and 30 mg/kg of this drug. The effects of cocaine and chlordiazepoxide on response rates maintained by avoidance of timeout from food presentation were unlike those reported when subjects responded to avoid shock presentation. The results of this experiment thus provide evidence to suggest that the effects of drug administration on avoidance behavior may be a function of the nature of the consequent event to be avoided.     

Food stealing by young Norway rats (Rattus norvegicus)

Six experiments were undertaken to explore factors affecting young rats' (Rattus norvegicus) frequencies of stealing food from conspecifics when identical food is available in surplus. It was found that (a) rats would walk across a bed of pellets to steal the particular pellet a peer was eating, (b) frequency of stealing within a pair did not decrease over days, (c) rats stole unfamiliar foods more frequently than familiar foods, (d) younger rats stole from older rats more frequently than older rats stole from younger ones, (e) hungry rats stole more frequently than replete rats, and (f) rats that had stolen a pellet of unfamiliar food from an anesthetized conspecific subsequently exhibited an enhanced preference for that food. Results suggest that food stealing is a mode of active seeking of information about what foods to eat.     

Further Evidence that Social Interaction Reduces Conditioned Taste Aversions in Mice

Social interactions with other conspecifics affect food selection in mammals. A previous study suggested that male mice attenuate conditioned taste aversion (CTA) by lithium chloride after interacting with an unfamiliar male conspecific. The present study was designed to (a) examine whether interactions with a familiar conspecific would attenuate CTA and (b) investigate sex differences in the social attenuation of CTA in mice. Results indicated that interacting with a familiar conspecific of the same sex following poisoning attenuated conditioned taste aversions only in male mice. The results suggest that the familiarity of conspecifics was not a critical factor in the social attenuation of CTA. Discrepancies between present and previous findings are discussed.     

The effect of prior acquisition of food aversion on the poisoned‐partner effect

It has been suggested that poisoned conspecifics function as aversive unconditioned stimuli for rats. The present study examined whether the prior acquisition of food aversion could enhance this effect. In phase 1, subjects were given pairings of cocoa‐flavored pellets and a toxin. In phase 2, they were given the cocoa‐flavored pellets and later presented with a poisoned or nonpoisoned conspecific. Subsequent testing involved a choice between the cocoa‐flavored pellets and regular pellets. Prior exposure to a poisoned conspecific prevented extinction of the conditioned aversion. In contrast, exposure to a nonpoisoned conspecific allowed extinction of the conditioned aversion. These findings suggest that a rat's reaction to a stressed conspecific is affected by their prior experience of aversive events.     

Response of captive lowland gorillas (Gorilla gorilla gorilla) to different housing conditions: testing the aggression-density and coping models

Several studies have suggested that primates react differently to spatial reduction. In this article, the authors tested some general hypotheses on primate response to spatial reduction by studying the Apenheul lowland gorillas (Gorilla gorilla gorilla; Apeldoorn, the Netherlands). The frequency of conflicts did not greatly change between the 2 housing settings, thus not supporting the density- aggression model. Indoor, gorillas performed touching behavior more often and increased their level of reconciliation. These findings support the coping model. Indoor, the gorillas also maintained broader interindividual distances by increasing the levels of sitting alone, avoidance, and dismissing behaviors. In conclusion, the Apenheul gorillas modified selectively the distribution of some patterns typical of their behavioral repertoire in response to a high-density condition. Both avoidance and coping tactics were used, thus revealing high levels of behavioral flexibility in this species.     

The role of metabotropic glutamate receptors and cortical adaptation in habituation of odor-guided behavior

Decreases in behavioral investigation of novel stimuli over time may be mediated by a variety of factors including changes in attention, internal state, and motivation. Sensory cortical adaptation, a decrease in sensory cortical responsiveness over prolonged stimulation, may also play a role. In olfaction, metabotropic glutamate receptors on cortical afferent pre-synaptic terminals have been shown to underlie both cortical sensory adaptation and habituation of odor-evoked reflexes. The present experiment examined whether blockade of sensory cortical adaptation through bilateral infusion of the group III metabotropic glutamate receptor antagonist cyclopropyl-4-phosphonophenylglycine (CPPG) into the anterior piriform cortex could reduce habituation of a more complex odor-driven behavior such as investigation of a scented object or a conspecific. The results demonstrate that time spent investigating a scented jar, or a conspecific, decreases over the course of a continuous 10 minute trial. Acute infusion of CPPG bilaterally into the anterior piriform cortex significantly enhanced the time spent investigating the scented jar compared to investigation time in control rats, without affecting overall behavioral activity levels. Infusions into the brain outside of the piriform cortex were without effect. CPPG infusion into the piriform cortex also produced an enhancement of time spent investigating a conspecific, although this effect was not significant.