Conspecific aggression influences food carrying: Studies on a wild population of Rattus norvegicus

Laboratory rats, like many other animal species, transport food. Their behavior is influenced by factors such as food size, the time required to eat, travel distance, travel difficulty, and the availability of cover, etc. Recent versions of optimal foraging theory suggest that species that display such behavioral patterns do so in order to minimize risk to predation while at the same time maximizing food gain. Nevertheless, it is not clear that this explanation applies to rats, nor is it easy to investigate this problem in a laboratory. The results of the present study on urban feral rats show that their food handling behavior is similar to that of domestic rats. The results also suggest that food carrying can serve defensive as well as communicative functions. Aggression around food sources was high. Smaller rats always carried food and some large rats infrequently carried food, suggesting that the food carrying by smaller, subordinate rats may help them avoid conspecific aggression. The rats also vigorously attempted to steal food that was carried home by conspecifics. This result suggests that food carrying can redistribute food resources and inform conspecifics about food availability. The results demonstrate the utility of multilevel behavioral analysis and also demonstrate that for rats, food transport has functions other than predator avoidance, including avoidance of conspecific aggression and communication about food availability. © 1996 Wiley-Liss, Inc.     

Fallow deer tactic to compete over food with red deer

Small ungulates may compete with larger species through higher mobility, greater aggressiveness, and/or by larger group sizes. We observed a herd of approximately 100 red deer (Cervus elaphus) and 130 fallow deer (Dama dama) at the Žehušice Deer Park during supplemental feeding to determine whether fallow deer can displace red deer at feeding sites and to describe strategies used for displacement. Data were analyzed during the antlered period (AP) when males of both species had hard antlers and the cast period (CP) when all red deer stags had cast antlers, but fallow bucks were still in a hard antler. We conducted 41 observation sessions, 29 during the AP and 12 during the CP. In both periods red deer were more numerous than fallow deer at the feeding sites. Fallow bucks initially waited until red deer arrived at the feeding site, after which they attacked any red deer. Fallow bucks were more aggressive than red deer stags or hinds. When stags retaliated, the bucks turned their attacks toward hinds. During feeding sessions, attacks against hinds intensified, while bucks avoided encounters with stags. As a result, in most cases (90%), red deer vacated the feeding site before the supplementary food was depleted. In contrast, fallow does not compete with the larger red deer and selected other sources of food in the park. © 1996 Wiley-Liss, Inc.     

On the dual nature of maternal aggression in rats

Presentation of a natural predator, a cat, was used to differentiate elements of maternal attack by female rats on a male intruder. Following exposure (without direct physical contact) of post-partum females to a cat or to a toy stuffed cat (control group), the females were replaced in their home cages and presented with a male intruder rat. Cat exposure reliably decreased lateral attack to the intruder, as well as locomotion, but had no effect on either jump attack or an upright defensive posture (boxing). Since predator exposure produces a somewhat durable increase in defense, along with inhibition of nondefensive behavior, these results suggest that maternal aggression represents a mixture of offensive, usually related to competition, and defensive (protective) behaviors. The results indicate that maternal aggression, as a parental care behavior, appears to be at least partially resistant to fear. © 1996 Wiley-Liss, Inc.     

Life spans in mice from strains selected for high or low aggression

The present study assessed the life spans in two lines of mice selectively bred for high (Turku Aggressive, TA) and low (Turku Nonaggressive, TNA) levels of aggression. The maintained parental Swiss albino strain (N), normally distributed with regard to aggression, served as a control line. It was found that the TNA males had a significantly shorter life span than the other lines of mice of both sexes. The relative early death of the TNA males was discussed in terms of male age-related decline of inherited low levels of catecholamine and androgenous hormone concentrations. © 1996 Wiley-Liss, Inc.     

Intruding male red swamp crayfish,Procambarus clarkii,immediately dominate members of established communities of smaller,mixed-sex conspecifics

The effects of competing asymmetries (intruder size advantage vs. prior residence) on dominance relationships were investigated in a laboratory setting. Sexually mature (Form I) male red swamp crayfish, 25%-27% larger than the average member of several mixedsex communities of 20-25 sexually mature conspecifics, individually intruded upon these communities on successive days. Each community was invaded once a day, with each of these large intruders invading every community once during the experiment. Five days after the last large intruder invasion, novel intruder group males, approximately the same size as the average community member, individually invaded the same communities, all communities being invaded once during a single day of testing. These novel intruders were used to differentiate the effects of intruder size from those effects of being put into a novel environment. During each intrusion, the frequencies of dominance, submission, aggressive standoffs, and nonaggressive interactions between the intruder and members of the community were recorded. The large intruders on each day immediately and virtually completely dominated all encountered community members, and the large intruders were significantly more dominant than the novel, smaller-sized intruders. The size advantage of the large intruders overwhelmed prior residence in influencing dominance outcomes, even in these well established communities. © 1995 Wiley-Liss, Inc.     

Construct validity of a competitive reaction-time aggression paradigm

This study tested the construct validity (convergent and discriminant) of a competitive reaction-time aggression paradigm. Seventy-nine males completed three trait aggression questionnaires and then competed on a reaction-time task whereby they received and delivered shocks to a fictitious opponent. Results demonstrated strong positive relationships between shock intensity administered and the trait measures of overt aggression but not with the measures unrelated to overt aggression. Results are discussed with regard to their contribution to the construct validity of the aggression paradigm used in this study. © 1995 Wiley-Liss, Inc.     

Grooming expresses harderian gland materials in the blind mole rat

The blind mole rat (Spalax ehrenbergi) is a highly aggressive and solitary rodent that shows the most striking physiological and behavioral adaptations to underground life. The eyes are not detectable externally; they are atrophied and covered by a thick layer of skin. A considerable part of the orbit is occupied by a very large Harderian gland. The current study demonstrates that during autogrooming the mole rat expresses Harderian gland materials from the conjunctival sac to the external nares and spreads them onto the fur. In contrast to other rodents, the mole rat's grooming behavior is usually confined to the front part of the body and does not progress after the head wipes to ventrolateral torso licking. Moreover, in highly aggressive encounters grooming sometimes ceases after the second phase-the nose wipe bouts. The unique first phase of the mole rat's grooming consists of highly rapid strokes over the skinny border of the head, which we assume help to squeeze Harderian materials from the gland. Unlike other rodents, in which grooming occupies a considerable part of their waking time, mole rats, cage individually, rarely perform autogrooming behavior. Grooming in mole rats has been found to be highly correlated with aggressive encounters, and submissive animals exhibit significantly more grooming than their dominant opponents. It is speculated that the Harderian gland discharge may serve as an appeasing substance when mole rats meet to reduce the extreme aggressiveness typical of these subterranean rodents. © 1995 Wiley-Liss, Inc.     

Anger and aggression during role-playing: Gender differences between hormonally treated male and female transsexuals and controls

A role-playing study on anger was conducted in order to identify the influence of sex hormones on individual and gender differences in irritation, anger arousal, and aggression. Different groups were studied: female-to-male and male-to-female transsexuals, with either group tested after 3 months of cross-sex hormone treatment, and untreated control women and men. All subjects were exposed to a 35-min videotape of an individual tested in an aversive, physically stressful, and frustrating situation in the laboratory. While watching, subjects were asked to imagine being in the same situation. Meanwhile, cardiovascular responses were registered and the intensity of moods and aggressive behaviour were assessed. Apart from a clear effect upon cardiovascular arousal and anger-related moods, there were also some interesting differences between the four groups, the most interesting one being a stronger aggressive response in the female-to-male transsexuals. Furthermore, interesting information was gathered with respect to the issue of whether role-playing and actual experimentation provide valid tests of anger and aggression in real life. © 1995 Wiley-Liss, Inc.     

Effects of frustration justification on hostile aggression

The present study tested Berkowitz' [1989: Psychological Bulletin 106:59-73] reformulation of the frustration-aggression hypothesis which states that any negative or aversive stimulus such as frustration, even if justified, will result in some measurable tendency to aggress, Participants' attainment of an expected gratification was either blocked in an unjustified manner, blocked in a justified manner, or not blocked at all. Degree of hostile aggression directed at the frustrating individual was measured. As predicted, justified frustration produced less hostile aggression than unjustified frustration, but even justified frustration produced more hostile aggression than no frustration at all. Results support Berkowitz' frustration-aggression reformulation. © 1995 Wiley-Liss, Inc.