Outcome Of Agonistic Interactions Research Articles

Redefining dominance calculation: Increased competition flattens the dominance hierarchy in dairy cows

Dominance hierarchies are known for mitigating conflicts and guiding priority of access to limited resources in gregarious animals. The dominance hierarchy of dairy cows is typically investigated using agonistic interactions, often monitored at the feed bunk right after fresh feed delivery when competition is high resulting in frequent interactions. Yet, the outcome of agonistic interactions during times of high competition may be more influenced by cows' high valuation of fresh feed than their intrinsic attributes, such that the dominance hierarchy constructed using agonistic interactions under high versus low competition times might differ. We tested how the structure of the dominance hierarchy changes in relation to different levels of competition in a dynamic group of 48 lactating dairy cows over 10 mo, with 6 cows exchanged every 16 d for a total of 159 cows. Using a validated algorithm we continuously detected the actor and reactor of replacement behaviors in 30 feed bins as cows competed for feed. We also calculated the percentage of occupied feed bins to characterize competition at the moment of each replacement. These data were combined to create hierarchies using Elo ratings, separately for 25 occupancy levels ranging from 13% to 100%. For each 1% rise in feeder occupancy, hierarchy steepness fell by 2.41 × 10-3 ± 9.71 × 10-5 (SE), and the percentage of dyads where both cows replaced each other rose by 0.13% ± 0.01%. At the highest feeder occupancy level in comparison to the lowest one, we observed 7.57% more dyads in which the dominant individual (those won more interactions at the lowest feeder occupancy) started to lose proportionally more. The magnitude of decrease in the winning rate of the dominant individual in those dyads also got amplified by 1.06 × 10-3% ± 1.37 × 10-4% (SE) for each 1% increase in feeder occupancy. These findings illustrate how inferred hierarchies vary with competition, with high competition flattening the hierarchy due to increased success of subordinate animals. We suggest that during heightened competition, increased valuation of resources can affect competitive success more than the individual's intrinsic dominance attributes. We recommend against calculating dominance hierarchies based on agonistic interactions during periods of high competition alone, and more generally urge researchers to differentiate agonistic interactions based on context when constructing dominance hierarchies.

White matter fractional anisotropy in a nonhuman primate model of early Alzheimer’s Disease‐like neuropathology: Relationships with social status and physiologic measures of stress responses

AbstractBackgroundPsychosocial stress is associated with micro‐ and macrostructural brain changes that may increase risk of Alzheimer’s disease (AD). White matter (WM) appears particularly vulnerable, and changes in white matter integrity are an early sign of AD pathogenesis. Cynomolgus macaques (Macaca fascicularis) have complex central nervous systems and naturally develop early AD‐like neuropathology with age. Female macaques form social status hierarchies in which subordinates exhibit behavioral and physiological signs of stress, and increased stress‐related pathologies similar to humans. Nonhuman primate studies provide a useful platform in which to assess relationships between stress and brain health is a well‐controlled environment with limited outside influences. Thus, these nonhuman primates are useful translational models for studying relationships of psychosocial stress with early AD‐like neuropathology.MethodUsing diffusion tensor imaging, we examined the relationship between psychosocial stress and fractional anisotropy (index of WM microstructural integrity (FA)) in 38 middle‐aged female cynomolgus macaques living in small social groups. Subjects were classified as either dominant or subordinate based upon the outcomes of agonistic interactions. FA in several regions of interest (ROIs): splenium, body, and genu of the corpus callosum (CC), frontal, temporal, occipital, and total cerebral and cerebellar white matter was assessed in relation to social status and several contemporaneous measures of stress physiology (blood pressure, resting cortisol, and heart rate variability (HRV)).ResultRepeated measures ANOVA using left and right ROIs as a repeated measure showed that dominants had significantly higher FA than subordinates in the genu and splenium of the CC, and the occipital and frontal cortices (all p<0.05). Dominants also had higher FA, on average, in the body of CC (p = 0.07) and cerebrum (p = 0.10), although these differences were not significant. Dominants and subordinates did not differ in temporal or cerebellar FA (both p>0.7). FA was inversely correlated with blood pressure, directly correlated with HRV (p’s<0.05), but not correlated with serum cortisol.ConclusionPsychosocial stress of subordination, as well as physiologic indices of stress responses, was associated with diminished WM integrity in several brain regions. These studies lay the groundwork for investigations of interventions on psychosocial stress to reduce AD risk later in life.

White Matter Fractional Anisotropy in a Nonhuman Primate Model of Early Alzheimer’s Disease‐like Neuropathology: Relationships with Social Status and Physiologic Measures of Stress Responses

AbstractBackgroundPsychosocial stress is associated with micro‐ and macrostructural brain changes that may increase risk of Alzheimer’s disease (AD). White matter (WM) appears particularly vulnerable, and changes in white matter integrity are an early sign of AD pathogenesis. Cynomolgus macaques (Macaca fascicularis) have complex central nervous systems and naturally develop early AD‐like neuropathology with age. Female macaques form social status hierarchies in which subordinates exhibit behavioral and physiological signs of stress, and increased stress‐related pathologies similar to humans. Nonhuman primate studies provide a useful platform in which to assess relationships between stress and brain health is a well‐controlled environment with limited outside influences. Thus, these nonhuman primates are useful translational models for studying relationships of psychosocial stress with early AD‐like neuropathology.MethodUsing diffusion tensor imaging, we examined the relationship between psychosocial stress and fractional anisotropy (index of WM microstructural integrity (FA)) in 38 middle‐aged female cynomolgus macaques living in small social groups. Subjects were classified as either dominant or subordinate based upon the outcomes of agonistic interactions. FA in several regions of interest (ROIs): splenium, body, and genu of the corpus callosum (CC), frontal, temporal, occipital, and total cerebral and cerebellar white matter was assessed in relation to social status and several contemporaneous measures of stress physiology (blood pressure, resting cortisol, and heart rate variability (HRV)).ResultRepeated measures ANOVA using left and right ROIs as a repeated measure showed that dominants had significantly higher FA than subordinates in the genu and splenium of the CC, and the occipital and frontal cortices (all p<0.05). Dominants also had higher FA, on average, in the body of CC (p=0.07) and cerebrum (p=0.10), although these differences were not significant. Dominants and subordinates did not differ in temporal or cerebellar FA (both p>0.7). FA was inversely correlated with blood pressure, directly correlated with HRV (p’s<0.05), but not correlated with serum cortisol.ConclusionPsychosocial stress of subordination, as well as physiologic indices of stress responses, was associated with diminished WM integrity in several brain regions. These studies lay the groundwork for investigations of interventions on psychosocial stress to reduce AD risk later in life.

Body size and canine size do not confer a competitive advantage in male rhesus macaques

Male armaments are hypothesized to have evolved under intrasexual selection. Such traits may function as signals, weapons, or both, in male–male mating competition. Primate sexually dimorphic canine teeth and body size are two potentially weaponized traits whose function as a signal and/or weapon remains unclear, largely due to the difficulty of collecting detailed measurements of morphology on large free-ranging mammals. Rhesus macaques, Macaca mulatta, are an interesting study system in which to investigate how such traits function because they experience relatively low levels of direct male–male mating competition compared to other members of their subfamily. Furthermore, male dominance rank is largely based on a queuing system rather than on the outcome of intermale aggressive encounters. We leveraged a novel data set of behavioural observations and morphometric data from free-ranging rhesus macaques to investigate the function of sexually dimorphic canine teeth and body mass as weapons and/or signals. We tested whether canine height or body mass was correlated with dominance rank, whether similarity in any of these factors influenced the occurrence or outcome of agonistic interactions between male–male dyads and whether either of these traits predicted the likelihood of winning an agonistic interaction. Neither canine height nor body mass was related to dominance rank. Similarity in dominance rank, but not in morphology, predicted the occurrence of agonism between dyads. Agonistic encounters between males more similar in dominance rank were more likely to be characterized by aggression rather than submission. Dominance rank, but not canine height or body mass, predicted the likelihood of winning an agonistic interaction. Our results suggest that canine height and body mass do not confer a strong competitive advantage in male rhesus macaques and add to a growing body of evidence indicating that weaponized traits do not always seem to function either in fights or as signals in male–male combat.

Psychosocial stress increases risk for type 2 diabetes in female cynomolgus macaques consuming a western diet

Chronic psychosocial stress is associated with increased risk of many chronic diseases including type 2 diabetes mellitus. However, it is difficult to establish a causal relationship between stress and diabetes in human studies because stressors often are self-reported and may be distant in time from metabolic consequences. Macaques are useful models of the effects of chronic psychosocial stress on health and may develop obesity and diabetes similar to human beings. Thus, we studied the relationships between social subordination stress – a well-validated psychological stressor in macaques – and body composition and carbohydrate metabolism in socially housed, middle-aged female cynomolgus monkeys (Macaca fascicularis; n = 42). Following an 8-week baseline phase, the monkeys were fed a Western diet for 36 months (about equivalent to 10 human years). Social status was determined based on the outcomes of agonistic interactions (X¯= 33.3 observation hours/monkey). Phenotypes collected included plasma cortisol, body composition, circulating markers of glucose metabolism, activity levels, and heart rate variability measured as RMSSD (root of mean square of successive differences) and SDDN (standard deviation of beat to beat interval) after 1.5- and 3-years on diet. Mixed model analyses of variance revealed that aggression received, submissions sent, and cortisol were higher, and RMSSD and SDNN were lower in subordinates than dominants (social status: p < 0.05). After 3 years of Western diet consumption, fasting triglyceride, glucose and insulin concentrations, calculated insulin resistance (HOMA-IR), body weight and body fat mass increased in all animals (time: all p’s < 0.05); however, the increase in fasting glucose and HOMA-IR was significantly greater in subordinates than dominants (time x social status: p’s < 0.05). Impaired glucose metabolism, (glucose > 100 mg/dl) incidence was significantly higher in subordinates (23%) than dominants (0%) (Fisher’s exact test, p < 0.05). These findings suggest that chronic psychosocial stress, on a Western diet background, significantly increases type 2 diabetes risk in middle-aged female primates.

Male dominance relationships in an extremely large chimpanzee community at Ngogo, Kibale National Park, Uganda

Abstract Male dominance hierarchies occur in many group-living primates and some non-primate mammals. Variation in aspects of agonistic relationships such as how many dyads show bidirectionality in aggression leads to variation in dominance hierarchies along a continuum from egalitarian (relatively small agonistic power differences between adjacently-ranked individuals, shallow hierarchies) to despotic (relatively large differences, steep hierarchies). Ranks usually depend mostly or entirely on individual characteristics that influence fighting ability (e.g., body size) and show inverse-U shaped relationships to age. However, coalitionary support sometimes also influences ranks. Chimpanzees (Pan troglodytes) form multi-male, multi-female communities within which males compete for status. Males typically form dominance hierarchies, and data from multiple study show that rank is positively related to paternity success. Males also often form coalitions and some dyads form long-term alliances. Effective coalitionary support can help individuals improve and maintain their ranks, and some evidence supports the hypothesis that coalitionary aggression generally, and the positions that males hold in coalitions networks specifically, influences paternity success. Hierarchy steepness varies among communities and within communities over time; variation in the number of prime-aged males per community is a likely source of this variation. Long-term data from an extremely large chimpanzee community with unusually many males, at Ngogo, Kibale National Park, Uganda, are largely consistent with previous analyses of male chimpanzee dominance hierarchies, but show several notable contrasts. Males at Ngogo formed significantly linear hierarchies and hierarchy steepness was greater than expected if the outcomes of agonistic interactions were random. However, variation in steepness did not show the significant inverse relationship to the number of “prime-aged” males documented for other chimpanzee communities and average steepness was high given the large number of males. Ranks showed an inverse-U shaped relationship to age, although individual rank trajectories varied considerably, but males attained their highest lifetime ranks at later ages and maintained relatively high ranks to later ages than those at other chimpanzee research sites. Two measures of coalition networks, strength and Bonacich power, showed significant positive relationships with male ranks. Strength is the rate at which males joined coalitions. Bonacich power is a measure of network centrality that assesses a male’s relational power, or influence (Bonacich, 1987): a male with high Bonacich power formed coalitions with relatively many other males who were also central in the coalition network, i.e., he was strongly connected to powerful others. On average, males also attained maximum values for these and other network measures relatively late and maintained relatively high values to relatively late ages. High coalition network strength, Bonacich power, and eigenvector centrality early in adulthood were associated with high peak ranks at later ages. However, the direction of causality between participation in coalition networks and ranks is not yet clear, and the effects of body size on dominance ranks and individual rank trajectories remains to be explored. Ngogo is a favourable habitat for chimpanzees and survivorship there is unusually high; this presumably facilitates the ability of males to maintain high competitive ability longer than at other sites and shifts rank trajectories toward older ages and leads to relatively steep hierarchies despite the fact that many male dyads have similar competitive ability. Future work will assess the impact of coalitions on dominance relationships in more detail and the relationship of coalitionary aggression to paternity success.

Intensity, rate, and outcome of agonistic interactions in harbor seals (Phoca vitulina concolor) vary with density on haul-out ledges

Due to successful conservation efforts, several marine mammal populations have increased in the past 40 years, leading to the possibility of increased competition for resources. We evaluated competition for haul-out space in western Atlantic harbor seals ( Phoca vitulina concolor ) by assessing agonistic interactions at 2 haul-out sites in Casco Bay, Maine. We predicted that intensity and rate of interactions increase as density increases, larger seals win more interactions than smaller seals do, seals already occupying a space win more interactions than arriving seals, and intensity of interactions is higher during molt but rates are higher during post molt. During molt at Gunpoint Ledge, 1 of the 2 sites, intensity of interactions decreased as density increased, but the pattern reversed during post molt. Rate of interactions peaked at intermediate density. Size and age class did not affect outcomes of interactions, but seals that already occupied space won more interactions than expected by chance. Interaction rate was higher during molt versus post-molt seasons. Harbor seals may experience increased competition for limited haul-out space as populations continue to grow, with seals occupying space outcompeting intruders.

Effect of phenology on agonistic competitive interactions between invasive and native sheet-web spiders

The phenologies of introduced relative to native species can greatly influence the degree and symmetry of competition between them. The European spider Linyphia triangularis (Clerck, 1757) (Linyphiidae) reaches very high densities in coastal Maine (USA). Previous studies suggest that L. triangularis negatively affects native linyphiid species, with competition for webs as one mechanism. We documented phenological differences between L. triangularis and three native species that illustrate the potential for the reversal of size-based competitive advantage over the course of the year. To test whether relative size influences interaction outcome, we allowed a resident spider to build a web and then introduced an intruder. We examined whether the outcomes of agonistic interactions over the webs were influenced by the species of the resident (invasive or native), the relative size of the contestants, and the species × size interaction. We found that the importance of relative size differed among species. In interactions between L. triangularis and each of two native species, size played a greater role than resident species on the outcome of interactions, suggesting that competitive advantage reverses over the season based on phenology-related size differences. Linyphia triangularis had a negative impact on the third species regardless of relative size.

The socio-matrix reloaded: from hierarchy to dominance profile in wild lemurs.

Dominance hierarchy influences the life quality of social animals, and its definition should in principle be based on the outcome of agonistic interactions. However, defining and comparing the dominance profile of social groups is difficult due to the different dominance measures used and because no one measure explains it all. We applied different analytical methods to winner-loser sociomatrices to determine the dominance profile of five groups of wild lemurs (species: Lemur catta, Propithecus verreauxi, and Eulemur rufus x collaris) from the Berenty forest (Madagascar). They are an excellent study model because they share the same habitat and an apparently similar dominance profile: linear hierarchy and female dominance. Data were collected over more than 1200 h of observation. Our approach included four steps: (1) by applying the binary dyadic dominance relationship method (I&SI) on either aggressions or supplant sociomatrices we verified whether hierarchy was aggression or submission based; (2) by calculating normalized David’s scores and measuring steepness from aggression sociomatrices we evaluated whether hierarchy was shallow or steep; (3) by comparing the ranking orders obtained with methods 1 and 2 we assessed whether hierarchy was consistent or not; and (4) by assessing triangle transitivity and comparing it with the linearity index and the level of group cohesion we determined if hierarchy was more or less cohesive. Our results show that L. catta groups have got a steep, consistent, highly transitive and cohesive hierarchy. P. verreauxi groups are characterized by a moderately steep and consistent hierarchy, with variable levels of triangle transitivity and cohesion. E. rufus x collaris group possesses a shallow and inconsistent hierarchy, with lower (but not lowest) levels of transitivity and cohesion. A multiple analytical approach on winner-loser sociomatrices other than leading to an in-depth description of the dominance profile, allows intergroup and cross-species comparisons.

Hierarchical decision making: resource distribution exhibits stronger effect on crayfish dominance relationships and shelter occupation than prior social experience and resource ownership

The outcome of agonistic interactions is critical to the acquisition of vital resources. These behaviours can be influenced by several intrinsic and extrinsic factors, and multi-faceted studies are necessary for ecologically relevant studies. The aim of this study was to combine the effects of past social experience, resource ownership, and the distribution of shelter resources to examine the combination of these effects on various measures of agonism in crayfish (Orconectes rusticus). Crayfish were assigned to one of three social conditioning treatments (naïve, subordinate, dominant) and then introduced to an arena where they were assigned to a resident or intruder treatment. An intruder shelter was then positioned 20, 60 or 120 cm from the resident shelter. We found that resource distribution (shelter distance) played a larger role in influencing agonistic behaviour than did past social experience or current social status.

The relationship between the comb and social behaviour in laying hens

The question of whether attributes of the combs of laying hens have any consistent relationship with dominance behaviour has yet to be answered unequivocally. This study sought to address this by investigating whether a relationship existed between the competitive ability of hens within stable groups and the size or colour of their combs. Pullets ( n = 120, Hy-line ® Variety Brown) were allocated randomly to eight groups of 15 hens for 32 weeks. Over this period the length and height of each hen's comb was measured regularly to estimate the total comb area and hens were weighed. In weeks 3–10 the aggressive interactions between hens in each group were observed to calculate a behavioural dominance score (David's score) for each hen. This score was based on the outcome of agonistic interactions with other group members; and accounts for the relative strengths of all opponents. Thus dominance scores reflected the competitive ability of hens from their overall within-group fighting success. The luminance, purity and dominant wavelength of the colour of each hen's comb was measured in week 27 using a telespectroradiometer. Hens with higher dominance scores had larger combs than those with lower dominance scores (gradient of slope = 0.008 ± 0.002, P < 0.001); this relationship was consistent across the experiment. There was no association between body weight and dominance score but there was a significant inverse relationship between dominance score and the dominant wavelength of the comb (gradient of slope = −0.067 ± 0.023, P < 0.01). This indicated that hens with combs perceived by humans as more yellow-red than pure red were generally more successful competitors. Further research is required to ascertain whether or not hens utilise this information on comb size and the underexplored area of comb colour to assess the competitive ability of their opponents.

Method for Assigning Categorical Rank in Female Pan troglodytes schweinfurthii via the Frequency of Approaches

Establishing the order of a dominance hierarchy among female chimpanzees (Pan troglodytes) is complicated by the fact that they often forage solitarily, and aggressive interactions between them occur infrequently. Authors of previous studies have typically ranked females via the direction of submissive pant-grunts and the outcome of agonistic interactions. Given that higher rank correlates with higher reproductive success in female chimpanzees, assessing rank is important but may be limited by sparsely populated dominance matrices. I tested the hypothesis that rank predicts the direction of female approaches. There is a significant relationship among Gombe females between the frequency with which a female was approached and her dominance rank. Dominant females approached other females less often than they were approached. Though approached frequencies failed to meet the criteria for formal rank indicators, they may be useful as real indicators of subordination. Because approach interactions occur far more frequently than pant-grunts, they may be useful in assigning categorical rank when traditional dominance metrics are limited.

Correlation of dominance as determined by agonistic interactions with feeding order in cats

To determine whether the direction of dominance as determined by agonistic interactions away from food was different from the direction of dominance as determined by access to a resource in cats. 28 cats. Dyadic relationships and hierarchy formed from observation of agonistic interactions away from food were compared with those formed from interactions at the food bowl. A cat was scored as subordinate to another cat if it lost 3 of 3 interactions or lost > or = 75% of the interactions when > 3 interactions occurred. Cats were observed for 449.4 hours. Hierarchy rank determined by agonistic interactions away from food was significantly correlated with rank determined by interactions at the food bowl. In 27 of 31 dyads, the direction of dominance was the same for food bowl and agonistic relationships, which was significant. In post hoc analyses, when considering the relationship between 2 cats, the heavier cat most likely ranked higher in each hierarchy; however, age was not significantly correlated with either hierarchy. On the basis of dyadic information, the older cat in a dyad was more often dominant in agonistic interactions. Males had a higher mean dominance rank than females; however, sex had no effect on rank determined by interactions at the food bowl. Factors influencing dominant-subordinate relationships are of interest for understanding and treating behavior problems such as aggression and resource control. The outcome of agonistic interactions away from food was related to, but not perfectly correlated with, the outcome of interactions at the food bowl, although winners of those agonistic interactions tended to have control of food.

Agonistic Behaviour in Crayfish: The Importance of Sensory Inputs

AbstractCrayfish have well developed sense organs, but clear-cut relationships with their behavioural use have hardly been established. We studied the possible use of vision, olfaction, and touch during agonistic behaviour, assuming that the outcome of agonistic interactions primarily depends on the input from one of these sensory organs. Agonistic encounters were studied in triads of crayfish, intact and with reversible blockage of vision, olfaction, or touch. Tension actions (threat, strike, fight, or avoidance) categorized as positive or negative depending on the crayfish initiating them, allowed us to identify the dominant and submissive animals. The contribution of sense organs to the outcome of interactions was tested during agonistic behaviour by blocking them (one at a time) after the establishment of a hierarchy (after-experiments) of before it (before-experiments). Under control conditions, a large number of contacts allowed animals to establish a dominance order on the first day of agonistic interactions, and the number of positive contacts between animals diminished in subsequent days. Visual or chemical blockage in after-experiments did not change the dominance order, but positive contacts decreased or increased, respectively. Blinded-before animals established a dominance order in the first 3 days of agonistic interactions showing an elevated number of positive contacts during the observation period. A similar result occurred in anosmic-before animals. Results from crayfish in which antennae were immobilized were similar to those from controls. Results suggest that at least two sensory modalities are necessary to gather information about conspecifics. Once the order is established (learned) any one of the senses is sufficient to maintain it. We speculate that if a chemical compound is involved in the maintenance of the dominance order, it is released after localization of a conspecific by vision or touch, a manoeuvre that could minimize expenditure of a costly resource.

Consistency of individual behavioural characteristics of dairy cows in their home pen

The aim of this study was to identify reliable individual behavioural characteristics of dairy cows based on aspects of their spontaneous behaviour and their reactions towards behavioural tests performed in their home pen. The parameters measured were supposed to reflect how easily the behaviour of subjects is influenced by environmental stimuli. In addition, their overall activity and aspects of their agonistic behaviour were recorded. It was hypothesised that reliable measures of these behavioural characteristics are consistent over time and across situations. The spontaneous behaviour of 31 subjects kept in a loose-housing system was recorded throughout four consecutive days at intervals of 5 min using a telemetric system. For each cow, the total amount of locomotion/standing, the mean duration of lying periods, and an index reflecting the day-to-day variation of behavioural activity was calculated. An agonistic-index was calculated based on the outcome of agonistic interactions (i.e. pushes followed by a displacement) at the feeding rack. The reaction of subjects towards environmental stimuli was experimentally tested by a visual obstacle test, a tail fixation test, and an air puff test. All recordings were repeated three times at an interval of 1 month each. The duration of lying periods ( r s from 0.435 to 0.726), the time of locomotion/standing ( r s from 0.522 to 0.677), the agonistic-index ( r s from 0.449 to 0.658), and the reaction towards the air puff test ( r s from 0.535 to 0.782) were significantly correlated between repetitions. The reactions towards the visual obstacle were significantly correlated between the first and the second test repetition (exploration: r s=0.491, latency to cross: r s=0.496), and the values of both measures decreased across repetitions (both P<0.01). The reaction towards the tail fixation was not consistent over time ( r s from 0.083 to 0.562). All measures of the spontaneous behaviour were significantly correlated with one another ( r s from 0.457 to 0.715 and from −0.512 to −0.582), except the agonistic-index which did not correlate with the duration of locomotion/standing ( r s=−0.112). There was hardly any consistent relationship neither within the measures of the behavioural tests nor between the measures of the spontaneous behaviour and the behavioural tests. It is concluded that the measures of the spontaneous behaviour form reliable individual characteristics. Such measures may be useful to predict the stress responsiveness of individuals in advance.

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.

Role of Familiarity in Structuring Male–Male Social Interactions in the Cockroach Gromphadorhina portentosa (Dictyoptera: Blaberidae)

We examined the influence of prior social experience on the outcome of agonistic interactions between male Madagascar hissing cockroaches, Gromphadorhina portentosa (Schaum). Males were placed randomly in pairs and allowed to form stable dominance-subordinance associations (original pairs). Two types of social conditions were then examined. Treatment pairs were composed of either familiar males (the males were re-paired with the same male that they had interacted with previously) or unfamiliar individuals (males were paired with a male that they had not interacted with previously). Males in familiar pairs maintained their rank during subsequent interactions. However, males in unfamiliar pairs lost their rank, indicating that familiarity of the opponent and not past experience of winning or losing an encounter determined the outcome of interactions. We also compared the behavior of individual males in the treatment groups with their behavior in the original pairings. Previously dominant males decreased their levels of aggression and hissed less when interacting with unfamiliar opponents. Previously subordinate males were more aggressive and hissed more in unfamiliar pairs. As a result, overall levels of behavior displayed in pairs of males did not differ. Aggression and hissing appear to be important in the maintenance, rather than the establishment, of relationships between G. portentosa males. We also discuss the possibility that agonistic hissing functions in individual discrimination rather than as a status cue.

Heat and social stress effects on pig immune measures1

Forty-eight domestic pigs were used to evaluate the effects of heat and social stress on immune indices. Pigs were brought together in groups of three per pen and video-taped for the first 72 h. Video tapes were viewed to determine time spent in aggressive and submissive behaviors. Social status of each pig was determined from outcomes of agonistic interactions. Pens of pigs were housed in either a thermoneural (control, 24 degrees C) or heat-stress (33 degrees C) air temperature. Immune measures were determined from blood samples obtained on d 0, 7, 14, 21, and 28 after grouping. Social status had an effect (P < .05) on lymphocyte proliferation in response to pokeweed mitogen: socially intermediate pigs had a higher proliferative response than socially dominant or subordinate pigs. Many immune measures showed a significant interaction between heat and social stress over days of the study. Generally, socially dominant or submissive pigs had alterations in immune function (elevated numbers of neutrophils, decreased antibody production) compared with socially intermediate pigs. In conclusion, heat and social stress interact in their effect on the pig's immune system. Although one might have predicted immunosuppression among submissive pigs, there also seemed to be immunological costs to dominant pigs as well. These data also have implications in design of stressor research in that social behavior should be measured or controlled.

Measuring Dominance and Constructing Hierarchies: An Example Using Mule Deer

AbstractImportant issues that are still unresolved in the study of animal social groups are how dominance is measured and how individuals are ranked. Based on observations of mule deer (Odocoileus hemionus hemionus), we constructed hierarchies for the same 26 bucks using five potential correlates of dominance and three measures based on the outcome of agonistic interactions. Data for each of six behavior measures were converted to ranks by six different numerical techniques.Different measures of behavior resulted in different hierarchies. This was especially so when the hierarchy based on sparring rates was compared to hierarchies based on other criteria. Although our results showed that dominance is not a unitary concept, several measures of dominance were highly correlated with one another. Thus, one measure, in some instances, may be a good but imperfect predictor of dominance defined by other criteria.For data sets based on index scores or rates of performing behavior, the mean difference and standard‐error difference ranking methods had distinct advantages. Both produced equally weighted ranks that minimized the effects of sampling errors.

Effects of ovariectomy, social instability and social status on female Macaca fascicularis social behavior

The effects of ovariectomy, social instability and social status on affiliative and agonistic behavior were studied in 44 females housed in 10 unimale groups. Five of the groups contained ovariectomized females and five groups contained intact females. The membership among three groups of intact females (n=13) and three groups of ovariectomized females (n=13) was reorganized every three months (unstable), and the other groups were left undisturbed (stable) for the 22 month study. The behavior of each female was recorded during 160 (stable) or 190 (unstable) 15 min focal observations of each subject. The social status of each female was determined by outcomes of agonistic interactions. It was hypothesized that the effects of social instability and status would be more pervasive than the effects of ovariectomy. It was found that ovariectomy reduced interfemale affiliation and increased male-female agonism. Social instability increased submissions to males and females and time spent alone, and decreased interfemale affiliation. Dominant animals were more aggressive and less submissive than subordinates. Thus, ovariectomy influenced both isosexual and heterosexual social interaction, implying mediation of these behaviors, at least in part, by ovarian hormones.