Resolution of agonistic conflicts in dyads of acquainted green swordtails (Xiphophorus helleri): a game with perfect information.

Conflict resolution of acquainted opponents was compared to that of unacquainted ones in Xiphophorus helleri males. Under the Familiar condition, the 2 males which met had settled contest against each other in a previously staged encounter in another aquarium. Thus one opponent was previously the dominant pair member, the other its subordinate. Under the Unfamiliar condition, 2 males met which were not acquainted with each other but had independently undergone previous experience of victory or defeat. We tested the hypothesis that familiar pairs would conform to some behavioural predictions of an asymmetrical game with perfect information. As for unfamiliar pairs, being imperfectly informed of asymmetries at contest onset, they would have to acquire information on these during the course of interaction (asymmetrical game with assessment) or alternatively would have to persist for a certain time or cost (war of attrition). All expectations derived from an asymmetrical game with perfect information applied to familiar pairs but not to unfamiliar ones. In familiar pairs, all previous roles were reinstated without any escalation. Though previous winners predominantly defeated previous losers under both conditions of cognizance, this difference was more extreme in familiar dyads than in unfamiliar ones. This suggests that the respective roles were less clearly identified in the latter. The costs of conflicts, both in terms of aggressive behaviours used and in time, were also higher in unfamiliar pairs than in familiar ones. Unacquainted individuals required a longer period to assess each other. In addition, they had to rely on more pugnacious behaviour to settle disputes in comparison to acquainted pairs. As expected also, familiar pairs being already cognizant of initial respective roles were more characterized in terms of the behavioural patterns typical of each of these roles. Differences between ultimate winners and losers were clearer in acquainted pairs and appeared earlier during conflict. It was also possible earlier during contest to discriminate and predict ultimate winners from losers of acquainted pairs using behavioural interactions. In unacquainted pairs, ultimate winners could be forecasted using multivariate discriminant analyses, mainly by their offering resistance to future losers. A `war of attrition' did not fit to unacquainted pairs.

The role of hen's weight and recent experience on dyadic conflict outcome.

This study simultaneously varied experiences of recent victory or defeat, 2-h familiarity with the meeting place, and hen weight in order to understand their combined effects on the establishment of dyadic dominance relationships between hens not previously acquainted with each other. Three kinds of encounters were arranged: (i) a previous winner unfamiliar with the meeting place met a previous loser familiar with the meeting place (n=28 dyads); (ii) a previous winner met a previous loser, both unfamiliar with the meeting place (n=27); (iii) a previous winner familiar with the meeting place encountered a previous loser unfamiliar with the meeting place (n=28). The weight asymmetry was combined with these three types of encounters by selecting hens showing various weight differences, in favour of the recent loser in 54 dyads and of the recent winner in 29 dyads. Results indicate that recent victory or defeat experience significantly affected the outcome. Even an important weight asymmetry, or familiarity with the meeting place were not sufficient for a hen recently defeated to overcome an opponent that was previously victorious. A 2-h period of familiarization with the meeting place did not provide any significant advantage over unfamiliarity. Although a significant relationship was found to exist between comb and wattles areas and the initial and final statuses, examination of partial correlations indicates that the influence was from initial status to final status, rather than from comb and wattles to final status. These results suggest that more importance should be attributed to recent social experience in comparison to intrinsic factors in determining dyadic dominance in the hen.

The role of recent experience and weight on hen's agonistic behaviour during dyadic conflict resolution.

Recent victory or defeat experiences and 2-h familiarity with the meeting place were combined with size differences in order to better understand their effects on the behaviour leading to the establishment of dyadic dominance relationships between hens not previously acquainted with each other. Three kinds of encounters were videotaped: (i) A previous winner unfamiliar with the meeting place met a previous loser familiar for 2 h with the meeting place (n=12 dyads); (ii) as in (i) but both were unfamiliar with the meeting place (n=12); (iii) as in (i) but the previous winner was familiar with the meeting place while the previous loser was unfamiliar (n=13). The weight asymmetry was combined with these three types of encounters by selecting hens of various weight differences: In 29 dyads the recent loser was heavier than the recent winner and in eight dyads it was the reverse. Recent experience had a major influence upon both agonistic behaviour and dominance outcome. Hens that were familiar with the meeting site initiated attacks more frequently than their unfamiliar opponent but did not win significantly more often. Recent experience and site familiarity could be used to identify 80% of future initiators. Once the first aggressive behaviour had been initiated, it led to victory of its initiator in 92% of cases. Weight was not found to influence agonistic behaviour nor dominance outcome. However, hens with superior comb and wattles areas won significantly more initial meetings than opponents with smaller ones. In the final encounters, victory also went more frequently to the bird showing larger comb and wattles, which happened also to be the previous dominant in a majority of cases. The use of higher-order partial correlations as an ex post facto control for comb and wattles indicates that they were not influential upon agonistic behaviour nor on dominance outcome, but were simply co-selected with the selection of victorious and defeated birds in the first phase of the experiment designed to let hens acquire recent victory/defeat experience.

Relative importance of initial individual differences, agonistic experience, and assessment accuracy during hierarchy formation: a simulation study.

This simulation study explores some conditions leading to transitivity within dominance orders. Combinations of three parameters were varied to study their consequences upon hierarchy formation and upon the degree of linearity of resultant structures. The factors studied were: (1) the importance of initial resource holding potentials (RHPs); (2) changes brought in RHPs by successive victories and defeats; and (3) accuracy of RHP assessment made by opponents. Results show that initial differences in RHP always lead to perfectly transitive chains whose rank order reflects the importance of initial differences. Even when simulated animals make important errors while assessing each other during round robin tournaments, emerging dominance structures are perfectly linear and ranks obtained in the structure are highly correlated with initial values in RHPs. Moreover, accumulated experiences of victory and/or defeat alone always lead to perfectly linear hierarchies. Their combination with initial individual differences in RHP led to the same conclusion. Even when assessment was far from being perfect, not only perfect chains were formed but initial values in RHPs significantly influenced rank order when the contribution of victory and defeat to RHP was relatively unimportant. The higher the importance of victory and defeat to RHP as compared to that of initial RHP values, the lower was the correlation between initial RHP values and the ranks order reached by individuals in the resultant hierarchies. In general also, the lower the variation within initial RHPs, the lower was the correlation between initial RHPs and ranks in the hierarchy. At a given level of initial RHP dispersion, increasing the contribution of victory and defeat to RHP diminished the correlation between initial RHP values and obtained ranks. In addition, inaccurate assessment reduced the overall correlation, especially when dispersion of initial RHP values was low and the contribution of victory and defeat relatively unimportant. These results shed some light on the controversy about the respective roles of initial individual attributes and that of patterns of resolution in the formation of animal hierarchies. We present the emergence of social order within closed systems as those simulated here as a case of self-organization.

The role of individual differences and patterns of resolution in the formation of dominance orders in domestic hen triads.

This research compares the role of initial individual characteristics to that of patterns of resolution in which successive dominance relationships are established during the formation of triads in the domestic hen. Combining weight and comb size with prior victory or defeat in the site of encounter, we created three levels of asymmetries of characteristics for triads of hens. The effects of these asymmetries were then examined on the resultant hierarchies and on the order of conflict resolution within triads under two different conditions of assembly. In one condition (simultaneous triad), the three hens were simultaneously introduced to each other and could thus freely choose their opponent. In the other condition (step-assembled triad), the hen predicted to occupy the highest rank was left on standby and introduced once the other two hens had settled dominance. This condition disrupts the normal process of hierarchy formation by imposing the first sequence of dominance settlement. We found that the structure of triadic hierarchies can be predicted from individual characteristics existing prior to hierarchy formation. No difference in the resultant structures were found between conditions of introduction, though different paths of conflict resolution were followed indicating that individual differences had a more determining role on the resultant hierarchies than patterns of resolution. In addition to demonstrating that individual differences determine resultant triadic structures, the present results also show that the same end structures can be reached by following resolution paths that are not necessarily of the Double Dominance and Double Subordinance types as prescribed by Chase's model. It is also found that in the simultaneous condition hens select each other to form pairs. Therefore, individuals do not meet at random but choose each other as opponents. The two hens predicted from individual differences to occupy the highest ranks first settle dominance, followed by settlement between the winner of the previous encounter and the bystander.

Coherent use of information by hens observing their former dominant defeating or being defeated by a stranger.

This study examines the role of observation during the formation of triads in female domestic hens. Results indicate that during hierarchy formation, a hen observing agonistic interactions and conflict settlement between its former dominant and a stranger uses this information when in turn confronted by the latter. Under a first condition (E, n = 15 triads), bystanders witnessed their prior dominant being defeated by a stranger before being introduced to them. In a second condition (C1, n = 16 triads), bystanders witnessed the victory of their prior dominant over a stranger. In a third condition (C2, n = 15 triads), bystanders witnessed two strangers establishing a dominance relationship before being introduced to their prior dominant and to a stranger the former had just defeated. The behavioural strategies of bystanders depended on the issue of the conflict they had witnessed. Bystanders of the E condition behaved as having no chance of defeating the stranger. They never initiated an attack against it, and upon being attacked, readily submitted in turn to the stranger. On the contrary, bystanders of the C1 condition behaved as having some chances against the stranger. They initiated attacks in 50% of cases, and won 50% of conflicts against the stranger. Under condition C2, bystanders first initiated contact with the strangers in only 27% of cases, which approximates the average of their chances for defeating the stranger. However, bystanders finally defeated the strangers in 40% of cases. These results suggest that bystanders of conditions E and C1 gained some information on the relationship existing between their prior dominant and the stranger and that they used it coherently, perhaps through transitive inference, thus contributing to the existence of transitive relationships within the triads. Alternate explanations are examined.

The role of individual differences in the formation of triadic dominance orders of male green swordtail fish (Xiphophorus helleri).

Triads of Xiphophorus helleri males composed of a large prior winner (A), a small prior winner (α), and a small prior loser (ω) were formed. In one condition, A was used as bystander while in another condition it was the small ω. The bystander could see through a transparent partition and observe conflict settlement between the two other fish without interacting with them. As soon as a dominance relationship clearly emerged, the partition was raised and the fish on standby could establish dominance relationships with them. The most frequent triadic structures obtained were A ≻ α ≻ ω and A ≻ ω ≻ α, indicating that individual characteristics played a determinant role in hierarchy formation. Patterns of assembly depended on individual differences of the fish. The fact that the same dominance structures were reached through various patterns of assembly suggests that individual differences are more determinant than paths of resolution in Xiphophorus.

Selecting dominants and subordinates at conflict outcome can confound the effects of prior dominance or subordination experience.

Individuals with a previous experience of dominance are likely to be dominants in further encounters. To test this effect, individuals with a previous experience of dominance are used for the experiments. One way to obtain such individuals is to let opponents 'self-select': encounters between pairs of more or less equivalent opponents are staged and one selects ex post facto the dominant and subordinate from the ensuing conflict. This paper formally shows that the selection of dominant and subordinate animals modifies the dominance probability functions of the two corresponding sub-samples of animals. As a result, the propensity of previous winners to win again and of previous losers to repeat their loss can be attributed to this artefact rather than to prior social experience. This result has serious methodological implications. When one relies solely on selection to obtain winners and losers, equiprobability is no longer the appropriate null hypothesis against which prior social experience effects have to be tested. To clearly demonstrate the effect of dominance experience, one must show that prior winners defeat neutral opponents in at least two-thirds of all cases; reciprocally, to show that prior subordinate experience plays a role, prior losers must win in less than one-third of all fights against neutral opponents; finally, to conclude that a combined effect of the two kinds of prior experience is in operation, one must obtain that prior winners defeat prior losers in more than 83% of all planned conflicts. The present result does not imply that experience effects are not at work when the selection procedure is used, but that the procedure used to show their effects is inadequate because effects of experience on a subsequent encounter are confounded with those introduced by statistical selection.

The effect of prior victory or defeat in the same site as that of subsequent encounter on the determination of dyadic dominance in the domestic hen.

We examined the effect of prior victory or defeat in the same site as that of a subsequent encounter on the outcome of dyadic encounter of domestic hens by placing them in two situations. In the first set of dyads, two unacquainted hens having experienced prior victory were introduced in the site where one had experienced victory. In the second set, two unacquainted hens having experienced defeat were introduced in the site where one had recently lost. Results indicate that victories are equally shared between individuals with prior victory experiences, while familiarity with the meeting site did not give any advantage. However, hens having previously lost were disadvantaged when the encounter occurred in the same site as that of their prior defeat. This demonstrates that previous social experience in a site is more important on the outcome of subsequent encounters for losers than winners. Losers seem to associate the site with the stressful effect of losing or being more easily dominated.

Social and spatial structure in brook chars (Salvelinus fontinalis) under competition for food and shelter/shade.

Salmonids, outside their reproductive period, are seen to have two types of territory called "territorial mosaic" and "partial territory". The first aspect of this research aimed at identifying the type of territory established by mature brook chars in artificial streams. After this, the biological value of spacing out was studied with regard to two resources: food, and shelter/shade which gives protection. Three 5 X 1 X 1 m artificial streams were built on the edge of a natural brook which provided a continuous water supply. One hundred and fifty mature brook chars (Salvelinus fontinalis) taken from that brook were distributed into 30 colonies with 5 members apiece. Three experimental conditions were created, and 10 colonies were submitted to each of these. In the first experimental condition, the quality of shelter/shade differed in 3 sectors of the artificial streams, whereas the quantity of food remained the same for all 3. In the second experimental condition, the quality of shelter/shade was identical, while the quantity of food differed in the 3 sectors. In the last condition, conflict was created: the fish had to choose between an area which offered excellent shelter/shade but no food, one which provided ample nourishment but no shelter/shade, and one in which all those resources were present at intermediate levels. Observation of the 30 colonies revealed "partial territory" in all cases. These corresponded to more or less complete aggressive-dominance hierarchies. Almost every alpha established territory, and the number of territorial individuals progressively decreased throughout inferior ranks. Alphas had exclusive use of their territory. Lower-ranking individuals successfully defended their territory against their subordinates, but were unable to drive away higher-ranking conspecifics. Overall results also indicated that the highest- ranking brook chars in the aggressive-dominance hierarchies more frequently established their territories in sectors of the streams with good shelter/shade than in sectors with good alimentary conditions.

An experimental model of aggressive dominance in Xiphophorus Helleri (pisces, poeciliidae).

An experimental model was constructed using seven postulates derived from the experimental results of Zayan (1974, 1975a,b,c, 1976). The model specifies the relative importance of several asymmetries in predicting aggressive dominance in Xiphophorus helleri . These asymmetries concern difference between duellists with respect to: prior residence in the tested area (vs intrusion); immediate social experiences of dominance or submission; social isolation; individual familiarity and recognition. The predictions of the general model were checked experimentally and confirmed; a multiple orthogonal regression accounted for about 97% of the variance in our experimental results. The basic experimental results serving as postulates were confirmed and could be generalized; a new synthetic and predictive model was formulated concerning the determinants of aggressive dominance in Xiphophorus .

Test of magnetic sensitivity in seven species of European birds using a cardiac nociceptive conditioning procedure.

An attempt was made to show magnetic sensitivity in seven species of European birds captured during their migration. The test was done on the following species: Streptopelia turtur (N=8), Streptopelia decaocto (N=2), Corvus monedula (N=6); one individual of the following: Corvus corone c., Turdus philomelos, Turdus viscivorus, Anas penelope. Most of the individuals were first subjected to conditioning to a light stimulus. They were then subjected to differential nociceptive conditioning to 100 presentations of a magnetic stimulus (CS+) reversing the vertical Z component of the local magnetic field and 100 presentations of a control stimulus for artifacts (CS-). The two stimuli were randomly interdigited. Cardiac activity was used as an index of reactivity throughout the study. Results indicate that the magnetic stimuli were not used by the birds as a cue presaging the forthcoming shock. We discuss the validity of the stimuli and paradigms used to demonstrate magnetic sensitivity in birds. These negative findings are related to possible artifactual effects explaining suggestive results in homing and zugunruhe experiments, and to local processing of magnetic effects without access to higher processes such as learning and arousal regulations.