Noninvolvement of testosterone in aggressive defense behavior in the male blind mole rat Spalax ehrenbergi

Blind mole rats (Spalax ehrenbergi) are solitary and aggressive subterranean rodents. Aggressive defense behavior in the mole rat functions to deter neighboring competitors from territory, food, and mates and includes seismic and odor signals. The aim of the present study was to determine whether the aggressive defense behavior displayed by male mole rats is testosterone dependent. Five behavioral variables were taken as being representative of such aggressive interaction: exposing teeth, biting, bulldozing movements of the head, soil blocking, and self‐grooming. We monitored male testosterone levels and aggressiveness throughout the annual cycle, which can be divided into three main climatic periods: cold and rainy (September–February); warm, during which the soil is still moist and easily excavated (March–May); and hot (June–August), when the soil is hard and dry. In a second experiment the effect of endogenous and exogenous testosterone on male aggressive defense behavior was determined before and after castration and following testosterone propionate replacement. We found fluctuations in male testosterone concentrations, with three peaks: in November, May, and August, one in each of the three climatic periods. However, these fluctuations did not correlate with male aggressive behavior, which remained constant throughout the year. Furthermore, because neither castration nor testosterone propionate replacement in castrated individuals affected their defense behavior, we suggest that such behavior in male mole rats is testosterone independent. The continuous excavation and maintenance of the mole rat’s underground tunnel system demands high energy expenditure year‐round and constant defense of territory sites and food caches from intraspecific rivals. Thus, although testosterone may fluctuate as a result of seasonal breeding cycles, constant high levels of aggressive defense throughout the year are crucial for the survival of the male mole rat in its solitary subterranean environment. Aggr. Behav. 27:64–72, 2001. © 2001 Wiley‐Liss, Inc.     

Defensive aggression in terns: Discrimination and response to individual researchers

The defensive responses of roseate terns (Sterna dougallii) were studied during the middle of the breeding season when all reproductive stages (incubation, chick-hatching, chick-rearing) were represented, to determine the factors affecting levels of nest defense and whether terns responded differently towards a familiar versus an unfamiliar researcher. Defensive aggression generally varied as a function of researcher identity, time of day, section or location in the colony and nest density. These variables explained from 60 to 66% of the variation in defensive aggression. More terns mobbed one researcher with more dive attacks than the other researcher. Terns were more aggressive in areas where the chicks had just hatched and were most vulnerable. © 1993 Wiley-Liss, Inc.     

Experimental evidence for aggressive antipredator behavior in black skimmers (rynchops niger)

We experimentally studied the aggressive antipredator behavior of black skimmers Rynchops niger nesting in a salt marsh and sandy beach with the use of a live herring gull Larus argentatus. Although there were no significant habitat differences in vegetation cover, distance from the edge of the colony, or nesting density, skimmers nesting in salt marshes were more aggressive toward the herring gull than were those nesting on the beach. Aggression increased during the first three minutes of the test, and decreased slightly thereafter. Aggression levels were highest when the gull moved compared to when it was stationary. Skimmers made few responses when a person was present with the gull, but aggression increased dramatically when only the gull remained. Our results suggest skimmers may engage in more aggressive behavior in defense of their nests than previously thought, particularly when exposed to a predator that actually takes eggs and chicks. Further, we suggest that conclusions about antipredator behavior drawn only from studies of interactions with people may need further amplification. © 1992 Wiley-Liss, Inc.     

A Rorschach Study of Narcissism Defense,and Aggression in Borderline,Narcissistic, and Cluster C Personality Disorders

We examined the differences between narcissism, mode of defense, and level of aggression on the Rorschach. We also investigated differences in borderline, narcissistic, and Cluster C personality disorders by examining responses to Rorschach content variables. The Lerner Defense Scale (P. Lerner & H. Lerner, 1980), the aggressive content section of the Holt (1977) method for assessing primary process manifestations, a modified version of Exner's (1986a) Egocentricity Index, Wagner's (1965) exhibitionistic M score, and grandiosity were scored on the Rorschach protocols of 17 borderline, I7 narcissistic, and 17 Cluster C personality disorders. Borderlines were found to employ primitive defensive structures to a greater degree and severity, show more intense and overall aggression as welt as more responses on the three forms of aggression in the Holt method, and have higher levels of grandiosity. Narcissists evinced significantly higher levels of egocentricity than borderlines and higher levels of idealization than the Cluster C group. Convergent validity was found on the measures of defense and aggression, which showed a strong relationship between primitive aggression and primitive defense.     

Aggression is associated with greater subsequent alcohol consumption: A shared neural basis in the ventral striatum

Alcohol use and abuse (e.g., binge drinking) are among the most reliable causes of aggressive behavior. Conversely, people with aggressive dispositions (e.g., intermittent explosive disorder) are at greater risk for subsequent substance abuse. Yet it remains unknown why aggression might promote subsequent alcohol use. Both aggressive acts and alcohol use are rewarding and linked to greater activity in neural reward circuitry. Through this shared instantiation of reward, aggression may then increase subsequent alcohol consumption. Supporting this mechanistic hypothesis, participants’ aggressive behavior directed at someone who had recently rejected them, was associated with more subsequent beer consumption on an ad‐lib drinking task. Using functional MRI, both aggressive behavior and beer consumption were associated with greater activity in the bilateral ventral striatum during acts of retaliatory aggression. These results imply that aggression is linked to subsequent alcohol abuse, and that a mechanism underlying this effect is likely to be the activation of the brain's reward circuitry during aggressive acts.

     

Social dominance and individual aggressiveness

Male rats exhibiting high, moderate, or low levels of offensive aggressive behavior in interactions with intruders in their home cage were grouped in mixed-sex colonies with 1 male of each aggression-level group in each colony. Agonistic interactions measured 1, 2, 3, 7, 14, 21, and 22 days after colony formation indicated that highly aggressive males on pretests continued to be more aggressive, becoming the dominant colony male in five of seven colonies and attacking intruders more often than less aggressive males. In the two remaining colonies the moderately aggressive male became dominant. This relationship, which was consistent over a number of indices, including offensive and defensive behaviors, and wound counts and wound sites, was seen even when a substantial weight differential favored the less aggressive animal. Dominance relationships were rapidly established and within-group fighting declined significantly over the 21-day test period. Pretest offensive levels also influenced the behavior of subordinates, with high or moderately aggressive subordinates showing more defense in interactions with dominants and receiving more wounds than did low-aggression subordinates. Dominant males also showed more defense in interacting with those subordinates which had been more aggressive during pretests. This pattern of results suggests that aggression level of the subordinate as well as the dominant may be an important factor determining the intensity of agonistic interactions in male rats.     

Neural correlates of intertemporal choice in aggressive behavior

People often have to make decisions between immediate rewards and more long-term goals. Such intertemporal judgments are often investigated in the context of monetary choice or drug use, yet not in regard to aggressive behavior. We combined a novel intertemporal aggression paradigm with functional neuroimaging to examine the role of temporal delay in aggressive behavior and the neural correlates thereof. Sixty-one participants (aged 18–22 years; 37 females) exhibited substantial variability in the extent to which they selected immediate acts of lesser aggression versus delayed acts of greater aggression against a same-sex opponent. Choosing delayed-yet-more-severe aggression was increased by provocation and associated with greater self-control. Preferences for delayed aggression were associated with greater activity in the ventromedial prefrontal cortex (VMPFC) during such choices, and reduced functional connectivity between the VMPFC and brain regions implicated in motor impulsivity. Preferences for immediate aggression were associated with reduced functional connectivity between the VMPFC and the frontoparietal control network. Dispositionally aggressive participants exhibited reduced VMPFC activity, which partially explained and suppressed their preferences for delayed aggression. Blunted VMPFC activity may thus be a neural mechanism that promotes reactive aggression towards provocateurs among dispositionally aggressive individuals. These findings demonstrate the utility of an intertemporal framework for investigating aggression and provide further evidence for the similar underlying neurobiology between aggression and other rewarding behaviors.     

Differential effects of the menstrual cycle on reactive and proactive aggression in borderline personality disorder

Borderline personality disorder (BPD) is characterized by rapidly shifting symptoms, including intense anger and aggressive behavior. Understanding how fluctuations in ovarian hormones across the menstrual cycle may contribute to symptom instability is key for accurate assessment of BPD symptoms and effective interventions. Reactive and proactive aggression, as well as anger-in and anger-out, were assessed daily in 15 physically healthy, unmedicated naturally cycling female individuals meeting criteria for BPD across 35 days. Urine luteinizing hormone surge and salivary progesterone were used to confirm ovulation and verify the cycle phase. Multilevel models evaluated cyclical differences of symptoms between cycle phases. Both forms of aggressive behavior demonstrated marked cycle effects, with reactive aggression highest during the midluteal cycle phase, co-occurring with initial increases in anger and irritability and followed by perimenstrual peaks in anger and anger-in. In contrast, highest levels of proactive aggression were observed during the follicular and ovulatory phases, when emotional symptoms and anger were otherwise at lowest levels. These findings highlight the importance of identifying the function of aggression when considering potential psychological and biological influences. Naturally cycling individuals with BPD may be at elevated risk for luteal worsening of a range of interpersonally reactive symptoms, including reactive aggression, whereas proactive aggression may occur more in phases characterized by less emotional and cognitive vulnerability and greater reward sensitivity. Research on aggression in this population should consider cycle effects. Cycling individuals with BPD attempting to reduce aggressive behavior may benefit from cycle-tracking to increase awareness of these effects and to develop appropriate strategies.     

Cross-fostering diminishes song discrimination in zebra finches (Taeniopygia guttata)

Song-production, -discrimination, and -preferences in oscine birds are dually influenced by species identity and the ontogenetic environment. The cross-fostering of a model species for recognition research, the zebra finch (Taeniopygia guttata) into heterospecific nests of the Bengalese finch (Lonchura striata vars. domestica) allows an exploration of the sensory limits of early development and the effects of species-specific acoustic cues upon song discrimination in adulthood. To quantify the song preferences of female and male normal-reared (control) and Bengalese finch fostered zebra finches, we recorded multiple behavioral measures, including spatial proximity, vocalization rates and response latency, during sequential song-playback choice-trials using both tutor species’ songs and the songs of two other ecologically relevant Australian species, the owl finch (Taeniopygia bichenovii) and the star finch (Neochmia ruficauda). Response strength was variable between the different measures, but no differences were detected within the specific behavioral responses towards the song playbacks of the two sexes. Control subjects strongly preferred their own species’ songs while Bengalese-fostered zebra finches exhibited reduced song discrimination between con-, tutor-, and heterospecific songs. Overall behavioral responsiveness was also modulated by social ontogeny. These results indicate a difference in the strength of preference for song that is dependent on the species identity of the rearing environment in oscine birds and illustrate the role of multiple behavioral measures and ecologically relevant stimulus species selection in behavioral research using zebra finches.     

Strain‐specific aggressive behavior of male mice submitted to different husbandry procedures

Severe aggression within groups of male laboratory mice can cause serious welfare problems. Previous experiments have shown that the transfer of specific olfactory cues during cage cleaning and the provision of nesting material decrease aggression and stress in group‐housed male mice. In this study, the combined effect of these husbandry procedures was tested for their long‐term effect on aggression in two strains of male mice (BALB/c and CD‐1). We used postcleaning aggressive behavior, wound counts, and testosterone levels as indicators of aggressiveness. Physiological responses to social challenge were investigated through urinary corticosterone and adrenal tyrosine‐hydroxylase measurements. Furthermore, the aggression‐modulating effects of two enrichment items (ShepherdShack/DesRes and PVC tube) were explored. Marked differences were found between the two strains. CD‐1 mice were more aggressive, had higher testosterone levels but lower corticosterone levels, and had fewer wounds than BALB/c mice. However, in neither of the two strains was long‐term enrichment with nesting material and its transfer after cage cleaning effective in lasting reduction of intermale aggression. This may be explained by the fact that aggression levels were generally low. It seems that housing mice in small, socially stable groups or keeping social disturbances to a minimum considerably modulates aggression in group‐housed male mice. Mice of both strains housed in cages enriched with nesting material had lower urinary corticosterone levels than standard‐housed mice. We therefore conclude that the long‐term provision of nesting material, including the transfer of nesting material during cage cleaning, may enhance the welfare of laboratory mice. Aggr. Behav. 29:69–80, 2003. © 2002 Wiley‐Liss, Inc.     

Habituation in songbirds

Songbirds respond to initial playback of a recorded conspecific song in numerous ways, from changes in gene expression in the brain to changes in overt physical activity. When the same song is presented repeatedly, responses have been observed to habituate at multiple levels: molecular, cellular and organismal. Core criteria of habituation have been established at each level, although in no case have all the formal parameters been rigorously measured. At the level of overt behavior, classical field studies showed that territorial birds respond to the song of a potential challenger with a variety of behaviors, and many (but not all) of these behaviors decline with repeated stimulus presentation. More recent laboratory studies have defined analogous responses to song presentation in the zebra finch (Taeniopygia guttata), the dominant species in current molecular and neurobiological research and one that does not use song for territorial defense. Studies in the zebra finch have also demonstrated activation followed by habituation of responses measured at both electrophysiological and molecular (gene expression and signal transduction) levels. In all cases, habituation is specific for a very particular stimulus – an individual song presented in a particular context. There are strong correlations between habituation measurements made at these different levels, but some dissociations have also been observed, implying that molecular, electrophysiological and behavioral habituations are not equivalent manifestations of a single core process.     

Reactive and proactive aggression in childhood: Relations to peer status and social context dimensions

Although there has been an accumulation of evidence to suggest a link between peer-directed aggression and social rejection, little attention has been given to the relations between specific subtypes of aggressive behavior and social rejection. The purpose of this investigation was to examine the relations between two subtypes of aggressive behavior (reactive and proactive aggression) and children's classroom peer status. The reciprocity of each of these subtypes of aggressive behavior and the social contexts in which these behaviors occur were also examined. Assessments of each of these forms of aggression among 70 boys (ages 5 and 6) were conducted using direct observations and teacher ratings. In general, directing reactive aggressive behavior toward peers was associated with social rejection, while utilization of instrumental aggression was positively related to peer status. The findings also indicated that directing proactive forms of aggression toward peers was related to being the target of proactive aggression. Finally, among older boys, both subtypes of aggression were more likely to occur during rough play than during any other type of play activity.     

Contribution of nesting experience to progesterone-induced incubation in ring doves (Streptopelia risoria)

Injections of progesterone induce incubation behavior in gonadally intact ring doves only if the doves have had previous experience with at least the nest-building phase of a breeding cycle. The present study was designed to determine whether exposure to progesterone during the nest-building phase is sufficient to account for the ability of progesterone to induce incubation at a later time or whether some other factor provided by experience with this phase of the cycle is needed. Six groups of 10 pairs of doves each were provided with different combinations of experience and progesterone priming. Progesterone priming combined with social isolation or with courtship experience had no significant effect on subsequent progesterone-induced incubation. However, doves that participated in the nesting phase of the cycle during progesterone priming later incubated in response to progesterone treatment. Nesting activity, which may or may not include building the nest, seemed to be the relevant experience.     

Aggressive behavior during the breeding season of adult female rhesus monkeys (Macaca mulatta)

The aggressive behavior of eight adult female rhesus living in a captive social group was studied prior to and during a breeding season extended by vasectomizing all the adult males in the group. Female reproductive status was ascertained by: recording all adult female-adult male copulations; detecting menstruation by vaginal swabbing; and analyzing serum progesterone levels by radioimmunoassay. Females showed more non-contact aggression during the breeding season, but wounding did not increase. Individual cycling females directed more frequent aggression to: particular adult males subordinate to them, subordinate females also in estrus, and (in a few cases) juveniles and infants.     

Hostile aggression and type A behavior

Type A and Type B male college students were given the opportunity to display hostile aggression against an insulting confederate on a bogus ESP task, using either aversive noise or a monetary penalty. Preliminary correlational analyses confirmed that Ss' aggressive responding covaried directly with their reported desire to hurt the confederate but was, in contrast, unrelated to their reported desire to help the confederate. Thus, Ss' aggressive behavior was motivated by hostile intentions. Subsequent analyses revealed that Type As were more aggressive and reported a greater desire to hurt the confederate than Type Bs, regardless of the mode of aggression. These data support the results of a recent study which questioned the intuitively appealing assumption that Type As should only display aggressive behavior when motivated by some external achievement goal.     

Distress and aggression during dating conflict: A test of the coercion hypothesis

Research with clinically depressed and maritally discordant couples suggests that women's distressed behaviors function to suppress their partners' subsequent aggressive responses. We applied this coercion hypothesis to a nonclinical sample of dating couples (N = 288). We further examined whether these effects were gender‐specific, and whether distressed and aggressive behaviors differ within physically violent versus nonviolent relationships. Women but not men reported engaging in elevated rates of distress in response to partner aggression during past dating conflicts. However, both women and men expected distressed behavior to suppress partner aggression during future conflicts. Expectations about the functional effects of distressed behavior did not differ for participants with physically violent partners versus nonviolent partners. However, participants in violent relationships reported enacting more distressed behaviors and had greater expectations for partner verbal aggression during future conflicts than did participants in nonviolent relationships. Future research may identify the early onset of dysfunctional interaction patterns in couples and concomitant psychological distress.     

An experimental approach to the study of learned aggression

The sensory contact technique increases aggressiveness in male mice and allows aggressive types of behavior to be formed as a result of the repeated experience of victories in daily agonistic confrontations. Some behavioral domains confirm the development of learned aggression in males similar to those in humans. The features are repeated experience of aggression reinforced by victories; elements of learned behavior after periods of confrontation; intent, measured by increase of the aggressive motivation prior to agonistic confrontation; and decreased emotionality, estimated by parameters of open‐field behavior. Relevant situation provokes increases in aggression (boundary aggression). This review summarizes data on the influence of positive fighting experience in daily intermale confrontations on the behavior, neurochemistry, and physiology of aggressive mice (winners). This sort of experience changes many characteristics in individual and social behaviors, these having been estimated in different tests and in varied situations. Some physiological parameters are also changed in the winners. Neurochemical data confirm the activation of brain dopaminergic systems and functional inhibition of serotonergic system in winners under the influence of the repeated experience of aggression. The expression of the neurochemical and behavioral changes observed in winners has been found to depend on the mouse strain and on the duration of their agonistic confrontations. Aggr. Behav. 26:241–256, 2000. © 2000 Wiley‐Liss, Inc.     

Violent phenotype in SAL mice is inflexible and fixed in adulthood

Violence was shown to be qualitatively different from functional hyper‐aggression in mice selected for high aggression namely Short Attack Latency (SAL), Turku Aggressive (TA) and North Carolina (NC900) strains. This study aimed at investigating whether this adulthood violent phenotype as seen previously in the SAL mice is fixed and hence behaviorally inflexible right from day 1 of the experiment or consequential, i.e., subject to gradual change from functional aggression to violence. The functionally hyper‐aggressive strains namely TA and NC900 strains served as controls for the study. Methodologically, behavioral (in)flexibility was studied using the overall sequential structure of agonistic behavior. In particular, intra‐individual variations in the overall agonistic behavior as well as offensive, pre‐ and post‐offensive behavior transitions, directly related to the resident–intruder interactions were investigated. The SAL mice showed the least intra‐individual variation in their overall sequential agonistic structure as well as a fixed offense‐oriented agonistic behavior of highest magnitude when compared with the other strains. Additionally, the pre‐ and post‐ offensive transitions were most salient in the functionally hyper‐aggressive TA and NC900 strains, whereas virtually absent in the SAL mice. Thus, the violent behavior of the adult SAL mice is behaviorally inflexible or fixed, whereas the functionally hyper‐aggressive behavior of the adult TA and NC900 mice is behaviorally flexible and constantly adaptive to the opponent behavior, over 3 days of repeated resident–intruder interaction. Aggr. Behav. 35:430–436, 2009. © 2009 Wiley‐Liss, Inc.     

Aggression: Appetite or aversion?—An ethologist's viewpoint

The term “aggression” has been used to describe practically all situations in which an organism threatens, damages, or kills another-with the exception of certain predator-prey relationships. As a result, a great deal of confusion and controversy has arisen as to the causal factors and functions of aggression. The main ethological hypotheses concerning the nature of aggression are put forward. In order to illustrate the divergence in causal factors and functions, differences in motivational, physiological, and ecological bases of aggression in two closely related fish species are described. A basic division of aggression into “self-defensive” and “property-protective” behavior is suggested, together with the parameters separating these categories on behavioral, causal, and functional bases. Mechanisms which enable motivational changes from one category to another to take place during a single encounter are discussed, these being pain stimuli and physical or psychological “cornering.” The importance of learning effects on fighting behavior are emphasized, especially their negative and positive reinforcing effects in relation to self and property defense. The biological significance of aggressive conditioning for the animal and the role of aggression in species maintenance are discussed.     

Adolescents’ Social Reasoning About Relational Aggression

We examined early adolescents’ reasoning about relational aggression, and the links that their reasoning has to their own relationally aggressive behavior. Thinking about relational aggression was compared to thinking about physical aggression, conventional violations, and personal behavior. In individual interviews, adolescents (N = 103) rated the acceptability of relational aggression, physical aggression, conventional violations, and personal behavior, and justified their ratings. Results indicated that adolescents’ views about relational aggression are complex. Although gossip was viewed as very wrong (comparable to beliefs about physical aggression), exclusion was perceived to be somewhat acceptable (less wrong than conventional violations, but more wrong than personal behaviors). With regard to associations between beliefs about aggression and aggressive behavior, the results indicated that beliefs about gossip were associated with gossiping behavior, and that beliefs about physical aggression were associated with physically aggressive behavior. No links emerged between beliefs about exclusion and exclusionary behavior. Implications and suggestions for future research are discussed within the frameworks of social domain theory and social information processing models of aggressive behavior.