Analysis of ultrasonic vocalizations emitted by residents during aggressive encounters among rats (Rattus norvegicus)

This investigation was concerned with the extent to which aggressive resident rats emit 40-70-kHz vocalizations and the effect of these signals on intruders. In Experiment 1, deafened and intact intruder males were given two encounters with resident animals. Deafened intruders engaged in a higher duration of immobile or freezing postures than intact animals. Experiment 2 indicated that the augmentation of freezing found among deafened intruders was not due to an inability to detect ultrasounds made by residents since intruders encountering devocalized resident males showed no reliable differences in specific motor patterns from intruders paired with intact residents. The results further demonstrated that 40-70-kHz vocalizations are produced almost entirely by intruding animals since there were no significant changes in occurrence of these calls when resident males were devocalized. Under the constraints of the testing procedures employed, the role of ultrasonic communication during the initial formation of agonistic relations could not be determined experimentally.     

Effect of residence and size asymmetries upon the agonistic interactions between juvenile white‐seabream (Diplodus sargus cadenati de la Paz,Bauchot and Daget, 1974)

The behavioural patterns of juvenile white‐seabream suggest that asymmetry in residence is an important factor governing the outcome of contest between individuals of this species. Asymmetries due to resident status had strong effects on agonistic behaviour, with asymmetries in body sizes producing weaker effects. Resident fish won all the combats against intruders of lower or similar length. However, when the intruder was larger than the residents (higher than 5% in length and 20% in weight), the percentage of combats won by the residents decreased to 85.7%. There was a significant correlation between fight intensity and size asymmetry in favour of the resident fish. The resident fish was more aggressive and persistent in attacks, and contests were more intense when the size of the intruder was greater. During agonistic interactions, the frontal attacks and lateral displays were more frequent when the intruders were similar or larger than residents. Attacks to the flanks and chases were more frequent in pairs where the intruders were smaller. Aggr. Behav. 25:297–303, 1999. © 1999 Wiley‐Liss, Inc.     

Analysis of ultrasonic vocalizations emitted by intruders during aggressive encounters among rats (Rattus norvegicus)

This investigation was concerned with the identification of the ultrasonic vocalizations produced by intruders during aggressive interactions and the role of these signals in agonistic behavior of rats. In the first experiment, experienced resident males were paired with both devocalized and intact vocalizing naive intruder males. Devocalization of the intruder males resulted in a drastic decrease in 50-kHz vocalizations and the elimination of all 22-kHz vocalizations. This almost total absence of ultrasonic vocalizations was not accompanied by any change in resident aggressive behavior or intruder defensive and submissive behavior. In a second experiment, naive intruders were tested with either deafened or intact resident males. Similarly, preventing residents from hearing intruder ultrasounds had no detectable effect on any aggressive behavior. These experiments are not consistent with the correlative evidence that intruder-produced 22-kHz vocalizations inhibit the aggressive behavior of the resident. The results also show that most of the ultrasonic vocalizations emitted during aggressive encounters are probably produced by the intruder.     

Different patterns of biting attack employed by lactating female mice (Mus domesticus) in encounters with male and female conspecific intruders

Attacks by resident lactating female mice were examined in a variety of situations. Relatively few attack bites to vulnerable body regions were seen when pairs of unfamiliar lactating females fought, establishing social status prior to communal nesting. Sexually naive male and female intruders were equally prone to attack by lactating females, but patterns of bite attack generated by them were very different; males received the more damaging attacks. More signs of "fear" were seen in the lactating females' responses to male rather than female intruders. Varied motivations may underlie attacks by lactating females directed to conspecific intruders. Defensive patterns of biting by lactating females are more consistently directed towards males, intruders that are more likely to harm or destroy the litter. Although attacks by females rarely thwarted infanticide by male intruders, the behavior may acutely protect parental investment.     

Effect of chronic ethanol administration on intermale aggression in rats

An experiment was performed to study the effect of chronic ethanol administration on intermale aggression in rats using a 24-hour resident-intruder test. During the resident-intruder test residents displayed virtually all of the agonistic behaviors, and intruders displayed virtually all of the defensive behaviors. Intruders treated with ethanol displayed more defensive behavior and elicited more agonistic behavior than control intruders. Twenty minutes into the resident-intruder test intruders showed the greatest increase in corticosterone (338% vs. 129%), while residents showed the greatest increase in testosterone (103% vs. 18%). On the 2nd day of the resident-intruder test intruders lost more weight than residents (21.5 g vs. 10.2 g). Plasma corticosterone levels remained elevated for the intruders, and in particular for those intruders displaying defensive behaviors regardless of the resident's behavior. Plasma testosterone levels remained elevated for those residents that were paired with intruders that displayed defensive behaviors regardless of the resident's behavior. The frequency and severity of biting attacks by ethanol residents was significantly greater than that of control residents. In addition, the locus of biting attack shifted from the upper back of intruders paired with control residents to the flanks, tail, lower feet, and ventral surface on intruders paired with ethanol residents.     

Effects of novel odors on intermale attack behavior in mice

Offensive, defensive, and nonagonistic social behaviors of resident male mice toward unfamiliar intruders were examined during exposure to the novel odors of chocolate or sheep's wool. Both novel odors reduced lateral attacks and boxing when compared to familiar sawdust odor. Chocolate, but not sheep's wool, also reliably increased flight behavior by residents. Neither social behaviors nor self-grooming were affected by these odors. The novel odors had no effect upon, or actually decreased, the defensive responses of intruders towards residents. The equivalent effectiveness of both predator and nonpredator odors in elevating risk assessment and suppressing attack during firsttime exposure, and the decreased potency of cat odors following repeated exposure, suggests that novelty contributes to the enhanced defensiveness seen among subjects during initial exposure to predator odors. © 1995 Wiley-Liss, Inc.     

Relationship between mousekilling and conspecific aggression in the male rat

In order to investigate the relationships between mousekilling and conspecific aggression, behavioral variables of killer and nonkiller rats were compared in a “resident-intruder” paradigm, in resident as well as in intruder animals. The occurrence of offensive items (offensive sideways, attack) was significantly higher in killer rats when they were residents; their corresponding opponents displayed more defensive behaviors. No significant difference in aggressive behaviors was noted when the comparison was done in the intruders. These results and those of previous studies suggest that there is a correlation between mousekilling and intraspecific offensive behaviors. Some similarities in the situations where both behaviors are elicited–eg, introduction of an unfamiliar intruder into a familiar environment–may contribute to the existence of such a correlation and the possibility of common mechanisms underlying both behaviors is discussed.     

Responses of dominant and subordinate male rats to the odors of male and female conspecifics

The resident-intruder paradigm was used to examine the effects of social dominance and individual recognition on odor preferences and urine-marking in male rats. Resident males were significantly more aggressive than intruders and spent more time investigating the odors of familiar intruders. Resident males urine-marked most over the odors of females and familiar intruders while intruders marked least over the odor of the familiar resident. Intruders did not avoid investigating nor marking over the odors of familiar resident males or other conspecifics. These results suggest that individual odors of male rats may be more salient than a general odor of dominance, and that the dominant males increase their investigation and marking over the odors of familiar subordinates but not unfamiliar subordinates. The importance of olfactory learning during aggressive interactions is discussed.     

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 intruder's 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 animal's aggressive response.     

The role of body weight in resident-intruder aggression

The behavior of male NIH Swiss mice of various body weights in the resident-intruder test of aggression was investigated. Mice were housed individually for 10 days prior to the test, and allocated to six groups. In the first three groups body weights of residents and group-housed intruders were matched, and the animals were divided into light, average, or heavy groups. In the last three groups weights of the intruder mice were either matched with the residents, or intruders were lighter or heavier than the residents. We found that light residents spent significantly less time in aggressive behaviors and longer time in defensive behaviors than the other two groups. The heavy mice showed most social investigation. The body weights of intruders were also shown to affect the behavior in the test: those residents which had light opponents spent a longer time in aggressive behavior than those which had matched or heavy opponents. The resident mice with heavy opponents showed most defensive behaviors. To study whether pharmacological manipulation may have different effects on behavior in the resident-intruder test in mice having different weights, animals of light, average, and heavy body weight received a low dose (0.8 g/kg) of ethanol 30 min prior to the test. We did not note any effect of ethanol on aggressive behavior in the three groups. The results suggest that body weight plays a significant role in determining the level of aggression and defensive behaviors in the resident-intruder test.     

Sex differences in aggressive behaviour in various strains of mice

Two nonalbino inbred (C57 BL/6 and C3H/He) and one albino strain (Swiss) of mice were compared for female aggression toward intruders: 1 in period of lactation, 2 in nonlactating state and (3) in nonlactating state but previously rubbed with urine of lactating females; and for male aggression toward familiar or unfamiliar opponents. The results showed that resident females of the C57 and Swiss strain vigorously attack lactating intruders introduced into their cages. This effect was mediated by urinary cues emitted by the latter mice. It was also shown that Swiss residents displayed aggression towards nonlactating females, irrespective of their strain. Groups of C57 residents reacted most aggressively towards Swiss females, less aggressively towards C3H intruders, but did not show any aggression towards their own nonlactating conspecifics. In contrast, none of the C3H resident female groups displayed aggression towards intruding females of any category or strain. The results also showed that the males of the three strains displayed little (Swiss and C3H) or no aggression (C57) towards familiar opponents, whereas they directed increased aggressive responses towards unfamiliar ones. Comparisons among the three strains of mice revealed that Swiss males were the most aggressive in either situation. On the other hand, the finding that C3H males showed aggressive responses suggested that male and female aggression are, in this strain, under separate genetic or hormonal control.     

Effect of competitor density on the aggressiveness of juvenile white seabream (Diplodus sargus cadenati de la Paz,Bauchot and Daget, 1974)

The number of aggressive interactions displayed by juveniles of Diplodus sargus cadenati increases progressively in proportion to the number of intruders, with an upper threshold of more than 16 to 18 intruder fish. Beyond this density, resident aggressiveness decreases. The number of aggressive interactions that the resident fish devotes to expelling each intruder shows a clear and significant tendency to decrease as competitor density increases. The resident fish is incapable of rapidly evaluating the outweighing of its capacity for defense. Moreover, the strategy of aggressive defense of the resource against the density of competitors does not seem to be only profitability criteria dependent, but rather there is also a significant influence of the ability to fight shown by the resident. Aggr. Behav. 29:279–284, 2003. © 2003 Wiley‐Liss, Inc.     

Comparison between BALB/cJ and BALB/cByJ mice in tests of social behavior and resident-intruder aggression

The behavior of male mice from two BALB strains, the BALB/cJ strain and the BALB/cByJ strain, was examined with a social behavior test and a resident-intruder paradigm. Prior to testing, the animals were isolated for 0, 2, 5, or 10 days. In the social behavior test the pairs of BALB/cJ mice spent more time in active social interaction than pairs of BALB/cByJ mice, although the latter strain showed more locomotor activity. BALB/cJ mice isolated for 5–10 days, when tested in a familiar environment were more aggressive than mice from the BALB/cByJ strain. In the resident-intruder paradigm, in which a resident BALB mouse was confronted with an intruder NIH Swiss mouse, the BALB/cByJ mice showed more social investigation in their home cage towards the intruders, but there were no significant differences between the two strains in the amounts of aggressive behavior exhibited. The results of these experiments suggest that there are some differences in the social behavior of the genetically related BALB/cJ and BALB/cByJ mice. However, the differences appear subtle and paradigm-specific.     

Male–male combats in a polymorphic lizard: residency and size,but not color,affect fighting rules and contest outcome

Theoretical models predict that the outcome of dyadic agonistic encounters between males is influenced by resource‐holding potential, resource value, and intrinsic aggressiveness of contestants. Moreover, in territorial disputes residents enjoy a further obvious competitive advantage from the residency itself, owing to the intimate familiarity with their territory. Costs of physical combats are, however, dramatically high in many instances. Thus, signals reliably reflecting fighting ability of the opponents could easily evolve in order to reduce these costs. For example, variation in color morph in polymorphic species has been associated with dominance in several case studies. In this study, we staged asymmetric resident‐intruder encounters in males of the common wall lizard Podarcis muralis, a species showing three discrete morphs (white, yellow, and red) to investigate the effects of asymmetries in color morph, residency, and size between contestants on the outcome of territorial contests. We collected aggression data by presenting each resident male with three intruders of different color morph, in three consecutive tests conducted in different days, and videotaping their interactions. The results showed that simple rules such as residency and body size differences could determine the outcome of agonistic interactions: residents were more aggressive than intruders, and larger males were competitively superior to smaller males. However, we did not find any effect of color on male aggression or fighting success, suggesting that color polymorphism in this species is not a signal of status or fighting ability in intermale conflicts. Aggr. Behav. 35:274–283, 2009. © 2009 Wiley‐Liss, Inc.     

The development of territorial-induced intermale agonistic behavior in albino laboratory mice

Male mice of the CF-1 strain (Mus musculus) were allowed to take up lone residence in a small territory consisting of a 60-cm enclosure attached by a tubular runway to a standard mouse cage with food, water, and bedding. A group of ten mice, each of which resided in its own separate enclosure for 24 hours, were more aggressive toward intruders than other groups of ten mice following six-hour residence periods, or no such residence. Aggression toward intruders increased in repeated weekly tests of the six-hour residents, but after four weeks of testing did not reach the maximum stable level displayed by the 24-hour residents over four weeks of testing. In another experiment, the 24-hour residence period of groups of 20 CF-1 male mice was disturbed by briefly removing the mouse from the enclosure, before introducing the intruder, at various intervals prior to testing. Removal of the resident five minutes before testing resulted in a marked decrease in aggression toward intruders. Although lesser decreases in aggression followed intervals of 30, 45, and 60 minutes, a 180 minute interval resulted in no appreciable effects compared to undisturbed controls. It is concluded that exposure to the stimuli provided by the enclosure results in an aggressive readiness in the resident mouse which reaches a high level within a 24-hour period.     

Effects of repetition and response deadline on associative recognition in young and older adults

The present study examined the joint effects of repetition and response deadline on associative recognition in older adults. Young and older adults studied lists of unrelated word pairs, half presented once (weak pairs) and half presented four times (strong pairs). Test lists contained old (intact) pairs, pairs consisting of old words that had been studied with other partners (rearranged lures), and unstudied pairs (new lures), and participants were asked to respond "old" only to intact pairs. In Experiment 1, participants were tested with both short and long deadlines. In Experiment 2, the tests were unpaced. In both experiments, repetition increased hit rates for young and older adults. Young adults tested with a long deadline showed reduced (Experiment 1) or invariant (Experiment 2) false alarms to rearranged lures when word pairs were studied more often. Young adults tested with a short deadline and older adults tested under all conditions had increased false alarm rates forstrong rearranged pairs. Implications of these results for theories of associative recognition and cognitive aging are explored.     

Ethological analysis of the male rat's socioagonistic behavior in a resident-intruder paradigm

The object of the present study was to assess the rat's socioagonistic behavior by means of ethological procedures. Two groups of male Wistar rats were used: 33 residents and 66 intruders. To allow reliable characterization of social and agonistic patterns, social interactions were increased by the isolation of residents and, on the other hand, both offense in residents and defense in intruders were increased by differences in weight, agonistic experience, and habituation to the enclosure. Encounters were videotaped, and the animals' behavior was analyzed by a 27-pattern ethogram and a software package made up to this end. Several patterns parameters were quantified, and two ethological mathematical models were employed: sequential analysis of preferential directions and cluster analysis based on similarities between patterns. Following mean latencies of the most frequent elements, the first four pattern sequences appeared to be the same in both groups of animals. From the fifth pattern on, residents displayed mainly dominance and threat, whereas intruders showed defensive and submissive patterns. Attack was also displayed by residents, but less frequently than dominance and threat. The alpha status was established by two sorts of domination, either through dominance and threat or by attack. The mean frequency of the intraindividual transition of patterns was higher in residents than in intruders. Pathway graphs, derived from sequential analysis, showed some common dyads, triads, or quadrads of patterns, but they basically defined different behavior structures in residents and intruders. Dendrograms, obtained by cluster analysis, allowed classification of patterns into behavior categories. The categories in residents were exploration, dominance, threat, and attack, and they encompassed 18 elements; in intruders the categories were exploration, dominance, and defense, and they consisted of nine patterns. A submissive category composed of three patterns could be also deduced considering similarity results. To summarize, six behavior categories were obtained: one “socioindividual” (exploration) and five “agonistic” (dominance, threat, attack, submission, and defense). In conclusion, the present study shows how ethological procedures may help to elucidate the rat's socioagonistic behavior and to classify the observed patterns into behavior categories.     

Pheromone‐mediated intrasexual aggression in male lizards,Podarcis hispanicus

Sex recognition is based on color signals in many species of lizards. However, olfactory stimuli are also clearly involved, and many species might rely primarily on chemoreception. We aimed to examine whether color pattern or odors, or a combination of both factors, induce the aggressive response of males of the lizard P. hispanicus. We experimentally manipulated the coloration and odor of male P. hispanicus, thereby creating groups with all combinations between coloration and odor of males or females. Using data from staged encounters, we compared the responses of resident males to the experimental groups of manipulated males and their response to unmanipulated individuals (males and females). Responding males reacted significantly more aggressively to intruders with male odors independent of their coloration, whereas intruders with female odors did not elicit aggressive responses but were preferentially courted, irrespective of their actual sex and body coloration. In addition, intruders with female odors elicited a higher number of tongue‐flick explorations than male odor ones. Comparisons with unmanipulated male and female intruders agreed with these expectations. Therefore, at least at close range, odoriferous cues seem to be more important than color patterns in sex recognition and intrasexual aggression by male P. hispanicus. We suggest that this might be a pattern commoner than expected in many species of reptiles.Aggr. Behav. 28:154–163, 2002. © 2002 Wiley‐Liss, Inc.     

Depressed nursing home residents' activity participation and affect as a function of staff engagement

Behavioral interventions for depression target activity engagement and increased positive reinforcement, particularly from social interaction. Nursing homes provide limited opportunity for meaningful social engagement, and have a high prevalence of depression. Often residents obtain most of their social contacts from staff members. We present intra-individual correlations among positive staff engagement, resident affect, and resident activity participation from behavior stream observations of residents who were participants in an ongoing trial of an intervention for depression. Sixteen residents were observed 6 times weekly for 8 to 45 weeks, 5 minutes per observation. Positive staff engagement during the observations was significantly correlated with resident interest and pleasure. Positive staff engagement was related to resident participation in organized group activity; however, residents tended to be more engaged and show more pleasure when in informal group activities, especially those residents receiving the behavioral treatment. Positive staff engagement was not related to time in activities of daily living. Results have implications for understanding mechanisms and potential targets of interventions for depression.     

The effects of negative reinforcement for irritable aggression on resident-intruder behavior

This experiment demonstrated that rats trained to display elevated levels of shock-induced aggression in a negative reinforcement paradigm displayed more boxing behavior than yoked control groups in a later test in which intruder rats were placed in the home cage of resident rats. Resident or intruder status did not affect the influence of the negative reinforcement procedure on the observed resident-intruder behavior of trained animals; however, naive intruders paired with trained residents displayed increased defensive behavior, suggesting that negative reinforcement for shock-induced aggression affected the behavior of these residents.