Dyadic Encounters Research Articles

Seasonal changes in and effects of familiarity on agonistic behaviors of rat‐like hamsters (Cricetulus triton)

The seasonal changes in agonistic behaviors and effects of familiarity on agonistic behaviors in wild‐caught adult rat‐like hamsters (Cricetulus triton) were observed in dyadic encounters in a neutral arena. The aggression of opposite‐ and same‐sex encounters became higher or remained the same during the non‐breeding season. This indicates that the hamsters were solitary during both seasons. Familiarity increased the aggression in male–male encounters and decreased the aggression in female–female encounters during both seasons. Familiarity also increased the aggression in female–male encounters during the non‐breeding season and had no effect on the aggression in female–male encounters during the breeding season. These results may be related to the hamster’s social structure. The more agonistic acts both male and female hamsters had, the more frequently they marked using flank glands during both seasons. This implies that flank gland marking can be used to advertise status and can be assessed by opponents to reduce the agonistic costs.

Attack and defense in conspecific fighting in tree shrews (Tupaia belangeri)

AbstractPrinciples of conspecific defense have been analyzed for rodents, in which specific target sites for biting by attackers on defenders serve as an important determinant of the actions involved in both attacker and defender behavior. In an effort to determine the generality of these principles, attack and defensive behaviors and target sites for biting attack were evaluated in a nonrodent species, the tree shrew (Tupaia belangeri). Brief daily and repeated conspecific dyadic encounters between adult, socially experienced males (dominants, attackers), and adult, socially naive males (subordinates, defenders) that had been transferred into the territory of the dominants, produced a polarization of attack and defense. The dominant males showed chase, chase attack, jump attack, and biting behaviors, while the subordinates displayed flight and freezing. The vast majority of bites, as well as wounds and bruises, were on the subordinates’ backs. These patterns are very similar to those previously found in rats and mice and suggest that the organization of fighting, with targets of biting (or other painful) attack serving as an important determinant of both attacker (dominant) and defender (subordinate) behavior, may show considerable generality across nonrodent as well as rodent species. Although relatively few wounds were found after 28 days of repeated and daily encounters, the subordinate tree shrews show a variety of behavioral, neuroendocrine, and central nervous changes, indicating that they are stressed by these encounters per se. Aggr. Behav. 27:139–148, 2001. © 2001 Wiley‐Liss, Inc.

Segregation of colony odor in the desert ant Cataglyphis niger.

There are two separate, and presumably opposing, processes that affect colony odor in the desert ant Cataglyphis niger: (1) biosynthesis and turnover of these chemicals by individual ants, and (2) homogenization of colony odor through exchange of cues. The first increases signal variability; the latter decreases it. The impact of these factors was tested by splitting colonies and monitoring the profile changes occurring in the postpharyngeal glands (PPG) and cuticular hydrocarbons. From each of two polygynous nests four daughter colonies were formed, three monogynous and one queenless. Thereafter, 10 ants from each were randomly selected each month, for three successive months, for analyses of their PPG and cuticular hydrocarbons. From two colonies we also obtained ants from a known matriline. Over time, there was a shift in hydrocarbon profiles of both the PPG and cuticular washes in each of the tested colonies. Moreover, by subjecting selected hydrocarbon constituents to a discriminant analyses based on their relative proportions, all of the daughter colonies (queenright and queenless) were distinguishable from each other and from their respective mother colonies. In each of the queenright daughter colonies, the queen profile was indiscriminable from that of the workers and often was in the center of the group. Full sisters were clearly distinguishable from their nestmates, emphasizing the genetic versus environmental processes that govern colony odor. The effect of time was always superior to the separation effect in contributing to odor segregation. Comparison of the Mahalanobis distances indicated that the shift in hydrocarbon seems to proceed along parallel lines rather than in divergence. However, there was no overt aggression between ants that originated from the different subgroups in dyadic encounters. It appears that in this species a three-month separation pe riod is not sufficient to change the hydrocarbon profile beyond the recognition threshold.

Behavioural correlates of spatial distribution in Wagner's gerbil Gerbillus dasyurus (Rodentia, Gerbillinae)

Summary. - Spatial organization of Gerbillus dasyurus in the Central Negev (Israel) is characterized by isolated aggregations of several individuals within a homogeneous habitat. We studied the behavioural interactions between individuals from the same and from different aggregations in male-male and female-female dyadic encounters on neutral arena. We tested the hypothesis that between-individual relationships , in G. dasyurus populations are in accordance with the « dear enemy » phenomenon (individuals show more aggressive behaviour upon detecting strangers than when sensing neighbours). The number of cohesive interactions between gerbils was much higher than that of agonistic behaviours. Male opponents in neighbour dyads demonstrated both agonistic and cohesive interactions significantly less frequently than opponents in non-neighbour dyads. No significant difference either in manifestation or in frequency of behavioural items were found between neighbour and non-neighbour dyads of females. Male encounters were more asymmetric than female encounters in terms of defensive behaviour, but not in terms of offensive behaviour. No difference in behavioural asymmetry between neighbour and non-neighbour encounters of both sexes was found. It is noteworthy that the defensive asymmetry was significantly higher than offensive asymmetry in male encounters.

Distinguishing kinds of prior dominance and subordination experiences in males of green swordtail fish ( Xiphophorus helleri)

In experiments, there are usually two general ways of obtaining dominants and subordinates to test for the effect of recent experience upon ulterior behavior and dominance. One is to ‘impose’ such an experience on the contestants by a priori deciding which individual of the pair will become the dominant and which will become the subordinate through the use of rigged contests. The second technique is to let contestants ‘self-select’ the winner and loser by waiting for the spontaneous outcome of dyadic encounters between two usually well matched opponents. These two techniques of obtaining dominants and subordinates probably represent extreme cases on a single continuum of investment made by animals to settle dominance. To test this, we compared dominants and subordinates obtained from these two techniques in Xiphophorus fish males. It was found that pairs obtained through rigged contest (R) were much more aggressive in subsequent encounters than pairs in which the dominant and subordinate could self-select (S). They recuperated more rapidly from handling, initiated contact earlier, took more time to assess each other, and fought for a longer period of time. Prior-winners and prior-losers of the R condition more frequently relied on aggressive behavior during contest than that of the S condition. As a consequence, prior-winners and prior-losers of the R condition won equally the subsequent contest. On the contrary, prior-winners of the S condition defeated their prior-loser opponent in a majority of cases. These results can be tentatively explained by the following principle, winning or losing against a well matched opponent would leave more ‘experience’ than winning over a much weaker opponent, or losing to a much stronger one. This reinforces the hypothesis that prior-experiences are not qualitative states but come in various degrees.

Intraspecific behavioural interactions in Apodemus microps : a peaceful mouse?

Social interactions of captive Apodemus microps Kratochvil et Rosicky, 1952 were studied in dyadic encounters.

Locomotor performance and dominance in male Tree Lizards, Urosaurus ornatus

Abstract1. The importance of locomotor performance to the social status of male lizards may lie in its effect on the outcome of agonistic interactions and territorial contests. Presumably, dominant males are able to acquire and defend larger territories, encounter more potential mates and have greater reproductive success.2. Therefore, the hypothesis that dominance status should covary with locomotor performance was tested using the Tree Lizard, Urosaurus ornatus.3. Two components of locomotor performance, maximum sprint speed and stamina, in males were measured. The former variable was estimated as the fastest speed on a 0·25‐m length along a 2‐m long racetrack. The second variable was measured as the elapsed time a lizard could sustain a walking pace on a canvas belt moving at 0·50 km h−1.4. The relative social status of size‐matched males was independently determined by staging paired encounters in a novel arena. Dominance was measured by behavioural scores of aggression and submission.5. The dyadic encounters resulted in the unambiguous determination of dominant individuals for 48 of 50 trials. Dominant males were significantly faster than submissive males. In addition, endurance capacity of dominant males exceeded the submissive males.6. Dominance behaviour and locomotor performance are strongly associated. Although the exact underlying mechanism is unknown, the results suggest a link between hormones, performance and behaviour in territorial lizards.

Pituitary–adrenocortical responses to the first dyadic encounters in male rhesus monkeys: Effect of dominance relationship

Pituitary–adrenocortical responses to the first dyadic encounters in male rhesus monkeys: Effect of dominance relationship

Male–female interactions and socio-sexual isolation of Mus spicilegus toward two other species of east-European mice, M. macedonicus and M. m. musculus

Social and sexual interactions were analysed as potential behavioural processes assessing reproductive isolation between the mound-building mouse, Mus spicilegus, and two other wild species, M. macedonicus and M. musculus. Dyadic encounters among strange M. spicilegus individuals and between M. spicilegus and the two other species members were conducted with females in an oestrus state. In intraspecific M. spicilegus encounters, there was a high incidence of close contact behaviours initiated by the females. In interspecific encounters M. musculus males and females and M. macedonicus females showed social interest toward their M. spicilegus protagonists, whereas the later behaved in an unfriendly or aggressive manner. Thus socio-sexual interactions shown by the different species seem to be sufficient to prevent any attempt to mate interspecifically. Arguments in favour of recognition against reinforcement hypothesis are discussed.

Development of agonistic behaviour and vocalization in croaking gouramis

The development of agonistic behaviour and vocalization in the croaking gourami Trichopsis vittata was studied from hatching to sexual maturity (4 months of age). Initial interactions started when fry were 11 days old and consisted of approach and flight in a feeding context. More complex threat patterns appeared during dyadic encounters as fish grew older. Lateral display (spreading of median fins in a lateral position) first occurred during the third week, circling shortly afterwards and pectoral fin beating when fish were 7 weeks old. Rapid pectoral fin beating was first accompanied by sound emission at 8 weeks. Initially, croaking sounds were built up mainly of a series of single pulses, each one produced by one pectoral fin. Later, single pulses gave way to double pulses. Furthermore, pulse period and number of pulses increased, while the dominant frequency of croaks decreased significantly with age. After vocalization was established, frontal display, mouth biting and retreat behaviour occurred at the age of 10 weeks. Initially, young exhibited vertical bars which gave way to dots and horizontal bars at 8 weeks when fish started to vocalize. The order of appearance of behavioural patterns during ontogeny corresponds to the order of appearance in fights between adults. This is the first study demonstrating that the ontogenetic development of social signalling comprises characteristic changes in behaviour, vocalization and coloration in a teleost fish.

Sound production and reproductive behaviour of the armoured catfish Corydoras paleatus (Callichthyidae)

Sound production during reproductive behaviour, dyadic encounters and distress situations was investigated in the callichthyid catfish Corydoras paleatus. Sounds were broad-band, pulsed, acoustic signals produced during abduction of the pectoral spines. Only males emitted trains of sounds during courting and trains of sounds of shorter duration during dyadic encounters. Several males, which are usually smaller than females, courted one gravid female without obvious cooperation or competition between them. During mating, one previously vocalizing male clasped the female's barbels with one pectoral spine and inseminated the eggs. The number of successful spawnings, days until spawning, and number of eggs laid was not related to the number of males (one, two or three) combined with one female. Males did not behave aggressively towards each other during courting or in dyadic encounters. In distress situations, when fish were hand held, both sexes and juveniles produced single sounds. The dominant frequency was negatively correlated with body size and the sound duration was positively correlated with relative length of pectoral spines (standardized to body length). This acoustical behaviour in C. paleatus differs considerably from Hoplosternum thoracatum, a representative of the callichthyine subfamily, in which vocalization was observed during territorial behaviour in males and aggressive behaviour in both sexes. This is the first report of a major difference in vocalizing behaviour within one teleost family.

Aggressive experience affects the sensitivity of neurons towards pharmacological treatment in the hypothalamic attack area.

Early investigators of brain stimulation-evoked complex behaviours (attack, escape, feeding, self-grooming, sexual behaviour) reported that experience may affect the behavioural outcome of brain stimulation. This intriguing example of functional neuronal plasticity was later totally neglected. The present experiment investigated the behavioural outcome of in vivo microdialysis perfusion of the glutamate agonist kainate and/or the GABAA antagonist bicuculline into the hypothalamic attack area (HAA) of (1) animals naive to dyadic encounters; (2) animals with a recent aggressive experience (the probe being implanted 6-24 h after the last of a series of dyadic encounters); and (3) animals with an earlier aggressive experience (probe being implanted 2 weeks after the last aggressive experience). On the experimental day, rats received two 5-min infusions during a dyadic encounter lasting 35 min with an unknown opponent. Flow rate was 1.5-2 microliters/min, drug concentrations were 1.8 x 10(-5) and 1.5 x 10(-5) M for kainate and bicuculline, respectively. Behaviour was analysed before, during and after perfusions. Only the combined kainate + bicuculline treatment had significant effects on behaviour at the doses studied. A significant increase in aggressive behaviour was elicited only in animals with a recent aggressive experience, while naive animals and with an earlier experience responded to the treatments by grooming. These results appear to support early observations indicating that one important aspect of brain stimulation effects is previous experience.

D 1 dopamine receptors and the reversal of isolation-induced behaviors in mice

In a previous study, it was demonstrated that the high rates of social reactivity exhibited by isolated male mice in a dyadic encounter were mediated, at least in part, by an increased sensitivity of the D 1 dopamine receptors. The present research was guided by the hypothesis that the behavioral effects of isolation are reversible, and that changes in dopaminergic function support this reversibility. To this end, mice selectively bred for high and low levels of aggression were reared in isolation from weaning (21 days) to puberty (45 days), at which point they were either assigned to groups or left in isolation until day 69. By comparison to the continuous isolation condition, mice that eventually formed groups exhibited significantly less reactivity in a dyadic test conducted on day 69, showed a reduced response to dihydrexidine (DHX), and a decreased density of D 1 dopamine receptors. This experiment provided evidence for the plasticity of the neurobiological system supporting reactive responses, and confirmed the view that its functional organization is open to experientially-induced changes.

Natural Variation in Horn Size and Social Dominance and Their Importance to the Conservation of Black Rhinoceros

The importance of behavioral ecology to evolutionary theory, zoo biology, and animal husbandry is well recognized (Caro 1994; Krebs & Davies 1984), but, despite the prevalence of global biodiversity issues, its contribution to in situ conservation has been limited (Soule 1986; Ulfstrand 1996; Clenmmons & Buchholz 1997). Populations of the world's elephants and rhinoceros have been decimated by poaching; in Africa, rhino conservation measures increasingly rely on protection in heavily guarded reserves (Brett 1990). Extreme measures have included dehorning and shooting poachers. Although the case has been made that social status in black rhinos (Diceros bicornis) is unaffected by horn removal (Lindeque 1990), it is less than convincing because neither the internor intrasexual consequences of asymmetries in horn size on dominance have been studied. To understand horn function, models of sexual selection have been applied to dimorphic ungulates (Jarman 1983; Packer 1986; Clutton-Brock 1988), but predictions do not fit black rhinoceros because (1) the sexes are similar in horn and body size, (2) secondary sex ratios are equal, and (3) mortal fighting, the highest recorded for any mammal, results in about 50% of the males and 30% of the females dying from combat-related wounds (Berger 1994). We report field data on 52 black rhinoceros of known horn and body size and 442 dyadic encounters from three sites in northern Namibia. Our results suggest that intersexual dominance is female-biased, that intrasexual dominance is related to horn mass in males but not in females, and that where asymmetries between horned participants exceed 10 cm, larger horns confer

Interacción social y dominancia entre dos especies de ardillas del desierto Spermophilus spilosoma y Spermophilus mexicanos de una zona árida del norte de México.

La interacción social y la dominancia entre dos especies de ardillas, Spermophilus spilosoma y Spermophilus mexicanas fue estudiada bajo condiciones de cautiverio en la Reserva de la Biósfera de Mapimí. Las pruebas consistieron en colocar una pareja de individuos que se encuentra en una arena cuadrada. Dicho encuentro o enfrentamiento recibe el nombre de encuentro o confrontación diádica. En nuestro estudio se realizaron un total de 130 encuentros diádicos, los cuales fueron medidos por medio de dos índices: un índice agonista y un índice de tolerancia. Cada índice midió la frecuencia comportamental de las confrontaciones realizadas por los individuos. Los resultados mostraron que en encuentros intersaxuales los machos de ambas especies, fueron más agresivos durante el apareamiento mientras que las hembras lo fueron durante la lactancia. Ambas especies disminuyeron su índice de agresividad durante la prehibernación. En encuentros intraespecíficos S. spilosoma exhibió más comportamientos de tolerancia, mientras que S. mexicanus, ardilla agresiva y dominante, mostró un alto índice agonístico excluyendo a la otra especie de las arenas y limitando su distribución espacial. Concluyendo, podemos mencionar que nuestros resiultados muestran marcadas diferencias comportamentalas entre ambas especies lo que puede apoyar la hipótesis de una reciente colonización de S. mexicanus al área de estudio, así como también, el que puedan vivir en simpatría en condiciones naturales.

Interindividual Variability in Swiss Male Mice: Relationship between Social Factors, Aggression, and Anxiety

In the present study we carried out a series of experiments in Swiss albino male mice to investigate a) the effects of previous social experience on the levels of anxiety in the elevated plus-maze (EPM) and b) whether the response of males in the EPM differs in relation to the different social status. In Experiment 1 we tested in the EPM male mice that received different social experience. Results showed that individually housing generally increased measures of anxiety in the EPM compared with the group-housing condition. Moreover, aggressive males, screened during dyadic encounters in a neutral cage, displayed the highest levels of anxiety relative to the other experimental conditions. In Experiment 2 male mice remained group-housed and were observed to record their social status. Results showed that those animals rated as socially dominant displayed a higher level of EPM anxiety relative to subordinates. From an ethological perspective our findings may be interpreted in terms of coping strategies, with aggressive/dominant animals typified by higher levels of risk assessment and open-arm avoidance than defensive/subordinate animals.

Formation of Colony Odor in Ponerine Ant Pachycondyla apicalis

The mechanisms operating in the formation and maintenance of colony odor in the ponerine ant Pachycondyla apicalis were studied using radioactive tracers. Using [l-14C]acetate as a precursor, the de novo biosynthesis and distribution of pentane-extractable lipids within the ant's body were followed. Twenty-four hours after injection, newly synthesized alkanes, alkenes, as well as more polar lipids were found in the postpharyngeal gland, the epicuticle, and internally. Ants that had their mouths blocked with beeswax possessed significantly less radiolabeled lipids (all classes measured) in the postpharyngeal gland but had augmented levels in the internal pool and the epicuticle. Both hydrocarbons and more polar lipids were exchanged between the respective postpharyngeal glands and the epicuticle. The transfer to postpharyngeal glands was highest when both ants had an open mouth or when the recipient ant had an open mouth but the donor's mouth was blocked. This suggests that the transfer to the postpharyngeal gland in this species is by allogrooming and not by trophallaxis. Transfer to the cuticle was low and comparable in all treatments. Behavioral observations during the first 6 hr of the dyadic encounters and in intact colonies confirmed that the ants did not engage in trophallaxis. The level of transfer to the postpharyngeal gland in P. apicalis was significantly lower than in representatives of other Formicidae subfamilies studied so far. We attribute this difference to the evolution of trophallaxis in the higher Formicidae.

Intercolonial encounters and xenophobia in the common mole rat, Cryptomys hottentotus hottentotus (Bathyergidae): the effects of aridity, sex, and reproductive status

The ecological constraints prevalent in arid environments have promoted the evolution of social groups with a high reproductive skew in mole rat species occurring there. Outbred social bathyergids face conflict between maintaining colony integrity to enhance personal foraging success and hence survival, and dispersal to maTimizr individual lifetime reproductive success (LRS). This conflict will be a crucial determinant of the response of colony members to the presence of foreign conspecifics. We investigated how ecological constraints, sex, and reproductive status influence die outcome of meetings between foreign common mole rats (Cryptomys hottentotus hottentotus) in a series of dyadic encounters. Individuals from two localities, at the extremes of an aridity gradient, were used to assess the effects of aridity. The efFects of sex and reproductive status were investigated by trials between individuals of differing sex and status. The arid population revealed substantially higher levels of rejection than the mesic population. Sex and status played a significant role in moderating individual response. For both populations, encounters between different-sexed individuals produced lower levels of rejection than those between same-sexed individuals. For the mesic site, rejection was greatest for encounters between reproductive animals. Conversely, for the arid site, the levels of rejection were comparatively high and comparable for all combinations of reproductive status. Ecological constraints, sex, and reproductive status are significant factors in interactions between foreign common mole rats, ultimately influencing individual survival, colony integrity and the differential LRS of all colony members. Our results provide insight into die evolution and maintenance of family groups within the bathyergids.

Differential effects of chlordiazepoxide on aggressive behavior in male mice: the influence of social factors.

The present study examined the influence of prior social experience on the effects of chlordiazepoxide (CDP; 5.0, 10.0 and 20.0 mg/kg) on intrasexual aggression in male mice. Prior to drug testing, animals were either individually housed or screened in dyadic encounters in a neutral cage. This novel method yielded four experimental groups comprising animals with different social experiences and different aggressive/defensive characteristics: 1) individually-housed males (I): 2) aggressive males (A); 3) counter-attacking males (C), which actively responded to but did not initiate attack; and 4) defeated males (D). Twenty-four hours after screening, animals were treated with CDP and subjected to a resident-intruder test with untreated intruders. Results indicated that the lowest dose of CDP (5 mg/kg) increased aggressive behaviour but only in A males. At higher doses (10-20 mg/kg), CDP reduced attacks towards intruders in A, C and I, but not D, males. In A and C males, the antiaggressive action of CDP was associated with a prosocial effect (increased social investigation), whereas in I males, reduced aggression was associated with an increase in fear-related behaviours. As these differential effects of CDP on intermale aggression cannot be fully explained by differences in behavioural baselines, present data highlight the importance of experiential background as a powerful variable in determining behavioural responses to benzodiazepines. Present findings therefore suggest that an understanding of drug effects on social behaviour demands consideration of biological variability in phenotype.

Are staged dyadic encounters useful for studying aggressive behaviour of arvicoline rodents?

We investigated the aggressiveness of adult prairie voles (Microtus ochrogaster) in dyadic encounters staged in different types of arena trials to determine if responses differed (i) between neutral arena trials conducted in the laboratory and resident–intruder trials conducted in the field, (ii) between trials staged before and after 3 months of isolation from social contact, (iii) between voles reared in the laboratory and voles reared in the field, and (iv) among trials staged with the same individual over time. Though rodents are usually expected to be more aggressive on their own home range, female prairie voles tended to be more aggressive in neutral arenas. Males showed no difference in aggression between trials held in neutral arenas and trials held in arenas placed in their home ranges. Aggressiveness was not affected by 3 months of isolation for either males or females, suggesting that recent social cues may not strongly influence aggressive behaviour in this species. Voles reared in the laboratory were significantly more aggressive than those reared in enclosed field populations, which suggests that direct comparisons of field and laboratory studies of aggressive behaviour may be suspect. Individuals showed little change in aggressiveness when tested over several weeks in three trials with different opponents. We conclude that encounters staged in arenas provide standardized estimates of aggressiveness that are robust to differences in testing procedures and are repeatable over time. Therefore, their continued use seems warranted for studying aggressive behaviour of voles and lemmings.