Killing Behavior Research Articles

Character Displacement in Australian Dasyurid Carnivores: Size Relationships and Prey Size Patterns

The four different assemblages of marsupial dasyuroid carnivores in Australia, comprising four species on the island of Tasmania and three different two-species assemblages on the mainland of Australia, present an ideal opportunity to test the theories of competitively based morphological character displacement. With males and females treated as separate morphospecies, four trophic characters that relate to killing and feeding behavior and skull length, as a measure of body size, were examined for evidence of morphological patterning, latitudinal size variation, and sexual dimorphism. The competitive basis for character displacement in intra- and interspecific variation in prey size was sought from dietary analysis at a field site. Even spacing in canine strength, but not in other characters, was found among species and sexes of quolls (Dasyurus viverrinus and D. maculatus), but not including the devil (Sarcophilus laniarius) or the thylacine (Thylacinus cynocephalus), in Tasmania. Even spacing was found in temporalis muscle size for all combinations of the four Tasmanian species. Canine breaking strength and muscle strength driving the canines can be construed as the most important trophic characters involved in prey capture, and therefore in determining the upper size of prey that can be handled. Even spacing was found in Tasmania, where there are two larger species in the guild, but not in any of the three mainland assemblages where the larger species of carnivores have been absent for many generations. The basis for the observed morphological patterning in killing behavior, evidence for even spacing in prey size, and partial character release on the mainland are consistent with the hypothesis of competitive character displacement. These size relationships result from a complex interplay of factors. Latitudinally correlated size variation has influenced an increase in body size and canine strength in D. viverrinus and an increase in body size in D. maculatus in Tasmania. This is countered by decreased canine strength in D. maculatus in Tasmania resulting from competitive character displacement. The result is character convergence. Sexual selection also influences size relationships.

Microwear on Canines and Killing Behavior in Large Carnivores: Saber Function in Smilodon fatalis

Canids and hyaenids display a high density of features of microwear on canine teeth that reflect their similarity in killing strategy. However, hyaenids tend to have a higher percentage of short and wide features (pits) because of the high percentage of bone in their diet. Canines of felids display relatively fewer features than canids and hyaenids, which suggest that felids apprehend prey by delivering deep, strong bites that result in less abrasion of the canines. I suggest that canids rely more heavily on their canines and incisors for feeding than do felids. Smilodon fatalis, a large saber-tooth cat from the Pleistocene of North America, is similar to living felids in having relatively few features of canines, but differs from cheetahs (Acinonyx jubatus) and African lions (Panthern leo) in having relatively more pits. S. fatalis showed no consistent similarity in features of microwear on canine teeth to six large carnivores (leopard, Panthera pardus; cheetah; African lion; spotted hyaena, Crocuta crocuta; African wild dog, Lycaon pictus; gray wolf, Canis lupus), which suggests that its killing behavior and possibly dietary preference differed from modern predators. S. fatalis may have avoided contact with bone during killing and feeding encounters, which caused fewer features to form on the upper canines.

The occurrence of killer, sensitive, and neutral yeasts in Brazilian Riesling Italico grape must and the effect of neutral strains on killing behaviour.

The occurrence of killer toxins amongst yeast in Brazilian Riesling Italico grape must was investigated by using the sensitive strain EMBRAPA-26B as a reference strain at 18 degrees C and 28 degrees C. From a total of 85 previously isolated yeasts, 21 strains showed ability to kill the sensitive strain on unbuffered grape must/agar (MA-MB) and 0.1 M citrate/phosphate-buffered yeast extract/peptone/dextrose/agar (YEPD-MB) media both supplemented with 30 mg/l methylene blue. The killer activity of only four yeasts depended on the incubation temperature rather than the medium used. At 28 degrees C, the strains 11B and 53B were not able to show killer action. On the other hand, strains 49B and 84B did not kill the sensitive yeast at 18 degrees C. The killer strain EMBRAPA-91B and a commercial wine killer yeast K-1 were employed to examine the sensitivity of the isolated yeasts on YEPD-MB and MA-MB at 18 degrees C. The sensitivity and neutral characteristics of yeasts were shown to be dependent on the medium and the killer strain. Interactions, including K-R-, K-R+ and K+R+ strains, simultaneously, have revealed that some K-R+ strains appear to protect the K-R- strain against the killer toxin. Sensitive dead cells, although to a less extent, also exhibited similar protection. Kinetic studies have shown that the maximum specific growth rates were higher for the 20B YEPD-MB-sensitive strains (mu(max) = 0.517 h-1) than for both the 91B (mu(max) = 0.428 h-1) and K-1 (mu(max) = 0.466 h-1) killer strains. The protective capacity of neutral or sensitive cells that contaminate a fermentation, as well as the higher maximum specific growth rate of sensitive yeasts, besides other factors, may preclude the dominance of a killer strain. This protective capacity may also reduce the risk of a sensitive inoculum being killed by wild-type killer yeasts in open non-sterile fermentation.

Effect of prey density on behaviour and development of the predatory mosquito, Toxorhynchites towadensis

AbstractThe effect of prey density on feeding behaviour, killing behaviour, and development of the predatory mosquito, Toxorhynchites towadensis, was investigated in the laboratory. The number of prey consumed per larva increased toward an upper asymptote as prey density increased. Prey consumption curves during fourth instar were concave at low prey densities but convex at high prey densities. This phenomenon was not observed during other instars. Killing without consuming any part of prey occurred at prey densities of 20 per container and over. The number of prey killed but not consumed increased linearly with the number of unconsumed prey in the container. Prey acquisition behaviour was not affected by prey densities during the prepupal period. Developmental time from first instar to adult emergence decreased with increasing prey densities, but remained constant at densities of 10 per container and over. Adult size increased with increasing prey densities but there was no effect at prey densities of 20 and over.

The role of serotonergic neuron system in the mouse killing behavior (muricide) of the rat

The role of serotonergic neuron system in the mouse killing behavior (muricide) of the rat

Heterogeneous binding and killing behaviour of human gamma/delta-TCR+ lymphokine-activated killer cells against K562 and Daudi cells.

Effector-target conjugates, formed by coincubation of lymphokine-activated killer (LAK) cells with either K562 or Daudi cells, were separated from single cells by Percoll sedimentation. The occurrence of various CD molecules (CD3, CD56, CD57, CD16, gamma/delta-TCR) was compared in both fractions. Only LAK cells expressing the gamma/delta T cell receptor (TCR) were found in a significantly increased percentage in fractions containing conjugates indicating that gamma/delta-TCR+ LAK cells were preferably bound to target cells at the time of separation. In order to determine whether gamma/delta-TCR+ LAK cells also show a preferred killing activity against the targets, cultures enriched with or depleted of gamma/delta-TCR+ cells were established. Against K562 cells, gamma/delta-TCR(+)-enriched cultures showed a greatly reduced killing activity compared to LAK bulk cultures or cultures depleted of gamma/delta-TCR+ cells. Using Daudi cells as targets the enriched fraction revealed a slightly increased killing activity compared to bulk cultures or depleted fractions. Preincubation of gamma/delta-TCR+ LAK cells with anti-gamma/delta or anti-CD3 mAb resulted in a distinct increase of the killing activity against K562 cells, but in only a slightly enhanced activity against Daudi cells. It is postulated that gamma/delta-TCR+ LAK cells use the same adhesion mechanism for both targets but that only Daudi cells express a specific ligand for the gamma/delta-TCR. Occupation of the gamma/delta-TCR/CD3 complex by mAb, however, seems to substitute for the absent epitope on K562 cells by eliciting stimulatory signals in gamma/delta-TCR+LAK cells which, in combination with the binding stimulus, trigger cytolytic activity.

Evaluation of xanthotoxol for central nervous system activity

Xanthotoxol (XT), 8-hydroxypsoralen, exhibited dose-graded sedative activity in dogs, cats, rats, mice and hamsters. At doses of 5–20 mg/kg intraperitoneally (i.p.) in cats and 3–100 mg/kg orally (p.o.) in dogs, XT blocked predatory mouse/rat killing behavior. In mice, XT (10–300 mg/kg i.p.) exhibited a dose-dependent reduction in locomotor activity but was less potent in this regard than reference diazepam (10–100 mg/kg i.p.). XT in mice (0.1–10.0 mg/kg i.p.) and in hamsters (0.1–10.0 mg/kg p.o.) antagonized amphetamine-induced hypermobility but was less potent than diazepam. XT elevated the electrical threshold in foot-shock-induced fighting behavior in rats. XT (0.1–30.0 mg/kg p.o.) potentiated pentobarbital-induced narcosis in hamsters at otherwise subeffective doses of pentobarbital. Conditioned avoidance responses in rats were not significantly altered with 1–3 mg/kg i.p. and 30–100 mg/kg p.o. doses of XT but 300 mg/kg p.o. blocked both conditioned and unconditioned response. Doses of 100–1000 mg/kg i.p. of XT in mice were used to study 48-h acute toxicity of XT and its LD 50 was estimated to be 468 mg/kg. Doses of 10, 40 and 80 mg/kg p.o. were used to study the chronic toxicity of XT in rats for 6 months and no side effects or abnormalities in reproductive activity or endocrine integrity were noted. The F 1 generation of rats from 6-month XT-treated parents were free of teratogenic effects.

Canine carnassials: character displacement in the wolves, jackals and foxes of Israel

Previous research implies that competitive character displacement in felids and mustelids of Israel is expressed by canine size. Anatomy and observed killing behaviour of canids suggest that canines in this group are less adapted for the stylized role they play in felids and mustelids. Thus we hypothesized that character displacement, if it exists in canids, should not be manifested more clearly by canine size than by other traits. Five sympatric and at least partially syntopic canids occupy Israel, while in North Africa the largest (wolf) and smallest (Blanford's fox) are absent. Sexual size dimorphism in Israeli canids is generally less than in felids and mustelids (in which we analysed each sex as a separate ‘morphospecies’), so we used mixed-sex samples to represent each species. The three largest species (wolf, golden jackal and red fox) are also represented by Middle Palaeolithic samples in Israel, and all three had larger carnassial lengths then. Carnassial lengths, canine diameters and skull lengths are all remarkable evenly spaced among the five recent species in Israel. In Egypt, no trait manifests significant equality. Despite regional fluctuations in size, the carnassial length ratios of the three smaller species (foxes) are strikingly constant (1.18–1.21) throughout the region, while the ratios for the three larger species (wolf, jackal and red fox), sympatric only in Israel, are larger (1.33–1.34). Finally, mean carnassial length of jackals is constant across North Africa, while skull length and canine diameter both increase from Algeria through Egypt. All three traits are larger in Egypt than in Israel. We tentatively ascribe the equal ratios in Israel to competitive character displacement, though this hypothesis is speculative because of numerous lacunae in knowledge of diet, killing behaviour, available resources and extent of food limitation. Furthermore, humans have greatly affected range, density and ecology of wolves and jackals in the last century. Larger sizes in the Palaeolithic may well be manifestations of Bergmann's rule. The constancy of carnassial length in North African jackals, notwithstanding a longitudinal cline in CBLs of these populations, and the constant ratio between jackal and red fox carnassial length are both consistent with a hypothesis of character release in the absence of the wolf.

Neural control of predatory aggression in wild and domesticated animals

The neural mechanisms of predatory aggression in laboratory animals were investigated in a variety of rodents and members of the order Carnivora. Experimental enhancement of brain serotonin (5-HT) blocked killing behavior in rats, mice, mink and silver foxes, indicating that there is a 5-HT inhibiting mechanism of predatory aggression in animals of different species. Suppressed killing behavior, at least in some strains of mice, does not depend for expression on the inhibitory effect of the brain 5-HT system, but is caused by the low tonus of the system activating predatory behavior. Long-term satiation of mink increased the level of 5-hydroxyindole acetic acid in the lateral hypothalamus and amygdala and enhanced the latency of predatory aggression. It is suggested that 5-HT represents a dietary responsive endogenous factor regulating predatory behavior in carnivores. Selection of Norway rats over many generations for tamed behavior towards man (domestication) leads to an increase in level and turnover of 5-HT in the midbrain and hypothalamus, but does not change predatory aggression. Substantially reduced defensive behavior of domesticated rats is thus unconnected with the neural mechanism of predatory aggression.

Are rats with genetic absence epilepsy behaviorally impaired?

Absence seizures in humans are characterized by unresponsiveness to external stimuli and inactivity. However, in typical generalized non-convulsive epilepsy in children, intellectual capacities are considered to be normal. Wistar rats from an inbred strain with spontaneous absence-like seizures were compared with rats from the outbred control strain in various behavioral tasks in order to detect possible impairments related either to the absence epilepsy or to occurrence of spike and wave discharges (SWD). Spontaneous circadian locomotion, exploratory activity in an open field, social interactions with an unfamiliar conspecific and mouse killing behavior were similar in both strains. Avoidance learning in a shuttle box or food reinforced learning in a Skinner test were unimpaired or even improved in epileptic rats. During performance of a learned task either in the Skinner box or in a conditioned sound-bar pressing task, SWD were suppressed in epileptic rats as long as they were working for reinforcement. SWD reappeared when the motivation to perform the task had declined: unresponsiveness to a conditioned stimulus was then observed during SWD. These data are in agreement with observations commonly described in children with typical genetic absence epilepsy.

Alterations of serotonin neurotransmission and inhibition of mouse killing behavior: II. Effects of selective and reversible monoamine oxidase inhibitors of type A

Three groups of rats were tested for mouse killing behavior after IP injection of selective and reversible type A monoamine oxidase inhibitors. The rats were either spontaneous killers, or non-killers which acquired killing behavior following para-chlorophenylalanine treatment or electrolytical destruction of dorsal and median raphe nuclei. Moclobemide (para-chloro-N-(2-morpholinoethyl)-benzamide), cimoxatone (3-(4-(3-cyanophenyl-methoxy)phenyl)-5-(methoxy) -2-oxazolidinone, MD 780515), toloxatone (5-(hydroxymethyl)- 3-(3-methylphenyl)-2-oxazolidinone) and amiflamine ((+)-4-dimethylamino-2, alpha-dimethylphenethyl amine, FLA 336 (+)) were used as selective and reversible monoamine oxidase inhibitors of type A. Cimoxatone, toloxatone and amiflamine inhibited mouse killing behavior of spontaneous killer rats without apparent sedation, whereas moclobemide was not efficient at doses which did not decrease locomotor activity. A similar inhibition of mouse killing behavior was obtained in spontaneous and serotonin depleted killer rats. The results are discussed in relation to the behavioral expression of serotoninergic supersensitivity in the three groups of killer rats described earlier using serotonin agonist and uptake inhibitors.

Canine tooth strength and killing behaviour in large carnivores

Bending strength of upper canine teeth is examined among living canids, felids, hyaenids and several extinct species including sabretooth cats, borophagine dogs and the dire wolf, Canis dirus. The tooth is modelled as a cantilever with an elliptical cross‐section. Using beam theory, the bending strength of the upper canine is calculated given a constant force applied to the canine tip. Results indicate that felids and hyaenids have relatively stronger canines than canids, particularly in bending about the anteroposterior (AP) rather than the mediolateral axis. It is suggested that canine shape reflects the forces produced during killing and feeding. As shown by an analysis of jaw muscle moment arms, felids and hyaenids have relatively stronger bites than canids. Moreover, the canines of hyaenids and felids are perhaps more likely to contact bone during feeding and killing and consequently may be subjected to larger and more frequent bending moments about the AP axis. The canines of sabretooth cats are shown to be more similar in shape and strength characteristics to those of living canids than felids, whereas those of the borophagine dogs and the dire wolf are closer to modern hyaenas.

Inhibition of mouse killing behavior by serotonin-mimetic drugs: Effects of partial alterations of serotonin neurotransmission

Rats which do not kill mice and which require mouse killing behavior after partial lesion of the serotonin neurotransmission, either by p-chlorophenylalanine treatment or by electrolytical lesions of dorsal and median raphe nucleus, were treated by IP injection of serotonin-mimetics. The following drugs were used: 5-methoxy-N-N-dimethyl-tryptamine and 8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide, serotonin-agonists, fluoxetine and citalopram, inhibitors of serotonin uptake. All these serotonin-mimetics inhibit mouse killing behavior without apparent secondary effects. When these compounds were tested on killer rats, a stronger antimuricidal effect was observed in rats having altered serotonin neurotransmission. These results support a role for the serotoninergic supersensitivity in a model of aggressive behavior.

Adrenal modulation of parental behavior in neonatally gonadectomized C57BL/6J male mice

C57BL/6J male mice ordinarily kill neonatal mouse pups even if they are rendered androgen deficient by neonatal castration. Experiment 1 showed that adrenalectomy during adult life significantly decreased the tendency of neonatally gonadectomized males to kill newborns. Experiment 2 demonstrated that testosterone exposure (via silastic implants) during adult life prevented the effects of adrenalectomy in that killing was elevated and retrieving was reduced in neonatally gonadectomized males. Adrenal androgens may be responsible for maintaining killing behavior in neonatally castrated C57BL/6J male mice.

Spontaneous mouse killing rats: Gentling and food deprivation result in killing behavior almost identical to that of rats with medial hypothalamic lesions

Rats that were found to kill a mouse spontaneously were divided into two groups. One group was left untreated and allowed free access to food while the other was gentled for 15 min/day and given only 15 g of food/day. Nonkilling rats were induced to kill mice by lesions of the medial hypothalamus. Seven to ten days after being divided into groups or subjected to brain lesions, each rat's behavior toward a series of stimuli was observed. The stimuli were a live mouse, a second live mouse, a freshly killed mouse, and a cotton wad. Food-deprived/gentled spontaneous killers and rats induced to kill by medial hypothalamic lesions each tended to attack with higher intensities and lower latencies than control spontaneous killers. The food-deprived/gentled spontaneous killers and lesion-induced killers (but not the control spontaneous killers) also attacked a dead prey moved vertically and then held onto the prey with sufficient intensity that their feet would leave the floor of the cage before they would release their grip on the prey. It is argued that the behavior of food-deprived spontaneous killers may constitute a more valid model of spontaneous mouse killing than that of sated spontaneous killers. The close correspondence between behavior toward a prey by lesion-induced killers and food-deprived spontaneous killers suggests that the lesion-induced killers fit this model of mouse killing remarkably well.

Serotonin's influence on predatory behavior of highly aggressive cba and weakly aggressive DD strains of mice

The effects of serotonin were studied on locust-killing behavior of mice from low (DD) and high (CBA) predatory aggressive strains. 5-HTP injected intraperitoneally (50 and 100 mg/kg) or 5-HT administered into the lateral ventricle (10 μg) significantly reduced locust-killing behavior in highly aggressive CBA mice. Imipramine (20, 30, and 40 mg/kg) elicited a dose-dependent inhibitory effect on predatory behavior. Fluoxetine (10 and 20 mg/kg) alone had a slight influence on locust-killing behavior but potentiated the action of the subthreshold dose of 5-HTP (25 mg/kg). Pretreatment with the blocker of 5-HT2 type receptors methysergide (2 mg/kg) abolished the inhibitory effect of 5-HTP. These finding indicate that serotonin of the brain exerts an inhibitory effect on predatory behavior in mice. In contrast, neither lesion of the dorsal raphe nucleus (although significantly depleting the brain serotonin) nor treatment with methysergide (2 mg/kg) induced locust-killing behavior in weakly aggressive DD mice. Low predatory aggressiveness in DD mice is suggested to be related to the low tonus of the mechanisms activating killing behavior rather than to excessive serotonergic inhibitory influences.

The Effects of Chronic Treatment and Withdrawal of Cns Depressants on Aggressive Behavior

Young adult CD-1 male mice were housed in individual cages throughout the study. Groups of 10 to 20 mice were given gradually increasing doses of delta-9-tetrahydrocannabinol (THC) at 6.25 to 25 mg/kg i.p., trifluoperazine (TFP) at 6 to 12 mg/kg p.o., phenobarbital sodium (PS) at 20 to 35 mg/kg p.o., morphine sulfate (MS) at 5 to 20 mg/kg i.p., methaqualone (MQ) 10 to 20 mg/kg p.o. or chlordiazepoxide (CDP) 10 to 25 mg/kg p.o. over four to six weeks to develop tolerance of these drugs. Following the development of tolerance, the drugs were withdrawn. On the fourth day of withdrawal, a young (3-4 weeks old) male mouse was introduced into the cage. When the intensity of the attack was measured by the percentage of animals that killed the intruder within four hours. The results indicated 0 to 4 percent in the controls, 50-54 percent for THC, 50 percent for TFP, 42 percent for PS and 57 percent for MS. In contrast, no killing behavior was exhibited by these mice after treatment with MQ or CDP. These data suggest that enhanced aggressive behavior, elicited by withdrawal from certain psychotropic drugs, may be measured by the killing (muricidal) behavior of isolated mice.

Effects of ethanol withdrawal on muricidal behavior

When naive rats of our colony were individually housed for 1 month with free access to laboratory chow and water as drinking fluid, 6% exhibited muricidal behavior. When naive rats of the same colony were similarly housed but received ethanol 20% in water as the sole source of drinking fluid (ll.5 g ethanol/kg/day), the percentage of killer rats was the same. However, when the rats were housed in similar conditions and submitted to a 1-day ethanol withdrawal, the percentage of muricidal rats increased to 25%. Ethanol intake in the same conditions as described above did not change muricidal behavior of spontaneous killers and did not induce killing behavior in nonkiller animals. GABA-mimetic agents administered IP blocked ethanol withdrawal-induced killing behavior as well as spontaneous muricidal activity.

Incidence of pup killing and parental behavior in virgin female and male rats (Rattus norvegicus): Differences between Wistar and Sprague-Dawley stocks.

The responses toward young shown by males and nulliparous females differed substantially between two outbred stocks of laboratory rats. Sprague-Dawley females showed maternal behavior either spontaneously (35% of the naive rats) or through concaveation (92% of the initially neutral virgins). Of the Wistar females, however, only 10% showed maternal behavior spontaneously, and only 29% of the neutral virgins came to behave maternally during 15 days of concaveation. Prepubertal cohabitation with lactating rats did not facilitate maternal responsiveness in adulthood in the Wistar virgin females. Of the Sprague-Dawley males, 50% showed paternal behavior spontaneously, and only 4% killed the young. Among the Wistar males, however, only 4% showed paternal behavior spontaneously, and 76% killed pups. Such profound differences between outbred stocks of rats may be a source of discrepancies between the results of studies dealing with the induction of parental behavior in nonlactating rats.

Incidence of pup killing and parental behavior in virgin female and male rats (Rattus norvegicus): Differences between Wistar and Sprague-Dawley stocks.

Incidence of pup killing and parental behavior in virgin female and male rats (Rattus norvegicus): Differences between Wistar and Sprague-Dawley stocks.