Inversion of initial dominance relationships following the interchange of roles of resident and intruder within pairs of male swordtail fish (Xiphophorus helleri)

This experiment consisted of 75 different pairs composed of two male adults Xiphophorus helleri meeting each other twice. On the first occasion, one of the fish was familiarized with the meeting place for 3h (resident) while its opponent was familiarized with another aquarium (intruder). Upon dominance of one individual over the other, the pair members were separated and returned to their respective home groups for 168 hours (7 days). After this period of separation, the same pair members were reunited and met while roles had been reversed: the initial resident became the intruder, and the initial intruder was given prior-residency. Individuals in the initial resident role defeated the initial intruder in a significant majority of cases (76%). On their second meeting, the newly established dominance relationship was noted in favour of the new resident in a significant majority of cases (82%), and in a reversed direction as compared to the initially established dominance order. This shows that prior-residence is a powerful determinant of dyadic dominance outcome in Xiphophorus males when fish show minimal size differences

Outcome of dyadic conflict in male green swordtail fish, Xiphophorus helleri: effects of body size and prior dominance

The relative contribution of prior experience and of size asymmetries to the determination of dyadic dominance between unfamiliar individuals was examined using pairs of green swordtail fish, Xiphophorus helleri. Three experiments were conducted to assess the extent to which superiority in size could override potential handicaps resulting from prior experience. These results indicated that prior experience accounted for dyadic dominance when the size advantage of a previously subordinate over a previously dominant opponent was less than 25 mm2. However, as the lateral surface of the subordinate fish increased, neither previous experience nor size differences clearly accounted for the outcome of dyadic conflict. Even when the size advantage of subordinate opponents was in the 126-150 mm2 range, size differences did not adequately explain the outcome. In conflicts between large previously subordinate and smaller dominant fish, there was evidence for an inverse linear relation between the effects of size and the likelihood of establishing dyadic dominance. In general, males with prior experience as subordinates had to be at least 40% larger than a previously dominant fish to win a significant proportion of conflicts. These results indicate that prior agonistic experience and body size effects can be additive when at the advantage of one opponent. These factors can also cancel each other out when in opposition, at least when size differences are not extreme. The results also confirm the main effect of both factors as well as their interaction in the determination of conflict outcomes for X. helleri

Conflict outcome in male green swordtail fish dyads (Xiphophorus helleri): Interaction of body size, prior dominance/subordination experience and prior residency

The relative contribution of asymmetries in prior experience, size, and prior residency to the determination of dyadic dominance between unacquainted individuals was examined using pairs of green swordtail fish, Xiphophorus helleri. Four types of encounters were staged between an intruder and a smaller resident: (1) both had experienced prior victory; (2) both had experienced prior defeat; (3) the intruder had experienced prior victory and the resident prior defeat; and (4) the intruder had experienced prior defeat and the resident prior victory. In a fifth condition in which two intruders met, one was a prior subordinate and the other a prior dominant smaller in size than its opponent. In all these encounters, the superiority in lateral surface of one fish varied between 0 to 30% over that of its opponent. Results showed that (1) when size differences between contestants were within the range of 0-10% and there was an asymmetry in prior social experience, conflicts were essentially resolved according to prior experience with prior winners systematically defeating prior losers; (2) prior residency of 3 hours was an advantage only when both opponents had experienced prior defeat before meeting and when size asymmetries were small (e.g. <20%). It was not an advantage between prior winners or between a prior winner and a prior loser; (3) when large size asymmetries existed (e.g. 20-30%), size uniquely determined dominance outcome and nullified other advantages or disadvantages due to prior social experience and prior residency; and (4) at intermediate levels of size asymmetries (e.g. 10-20%), size partially cancelled any advantage due to a prior victory, and gradually beacme the most important factor in accounting for victories

Relation between dominance rank, prior agonistic intensity and subsequent aggressive levels in winners and losers of dyads of male Green swordtail fish (Xiphophorus helleri)

Aggressive scores obtained in a mirror test 1h before an encounter were found to be a good predictor of victory in male Xiphophorus dyads showing less than 5% size differences. Out of 36 dyad members showing higher aggressive scores at pre-test, 28 obtained victory in the subsequent encounter. It was found that future winners were more aggressive than future losers to their own image in mirror tests before their encounter. Initial individual aggressive levels in mirror tests were also found to be a function of the rank the individuals occupied in their home hierarchies. The higher the rank, the higher was the individual aggressive level as measured by mirror pre-tests, as well as by post-tests. This relationship applied to future winners, as well as to future losers. The level of aggression reached during agonistic encounter was not a function of the social ranks the opponents occupied in their home hierarchies. Males in dyads composed of two omegas fought as fiercely as males in dyads of two alphas or two betas. No significant relationship was noted between the initial individual aggressive scores at mirror pre-test and the levels of aggression reached during encounters. We found in winners the existence of a significant correlation between the aggressive level they reached during agonistic encounter and a subsequent increase in aggressive levels at mirror tests 1h and 24h after victory. The more intense the agonistic encounter, the more important the subsequent increase in aggressive level in winners; an increase which was still detectable 24h after victory. However, prior alpha winners were apparently not as sensitive as prior betas and prior omegas to the aggressive level reached during the encounter since their mirror scores obtained after victory did not change when compared to their baseline at pre-test. After defeat, losers did not show any significant change in aggressive scores in mirror tests. Moreover, it was found that encounters in which a 1h resident met an intruder were in general less aggressive than encounters between two intruders. Experiential effects are discussed as instances of learning and generalisation

DES DIFFÉRENCES LIÉES AU SEXE DANS LES STRATÉGIES DE RÉPARTITION SPATIALE CHEZ DES POISSONS PORTE-ÉPÉE (XIPHOPHORUS HELLERi) MAINTENUS EN CAPTIVITÉ

The swordtail fish is a species particularly abundant in fresh water of Mexico and Central America. It is an ovoviviparous species, not really territorial which shows nip&#64979;right order. In this research, significant differences of spatial distribution have been found according to the position in the nip&#64979;right order and according to the sex of the fish. These differences bind with two external variables: the presence of sexual partners and the space available for the fish. The dominating males prefer a space partition allowing access to the females more than a compartment allowing access to more space in volume. They also chase their subordinates in the contiguous compartment of the aquarium. Females swordtails prefer the bigger compartment independently of the presence of conspecific males. These results are discussed in the light of reproductive strategies particular to each sex

Penning ionization-FT-ICR: Application to diesel fuel analysis

International audienceThe Penning ionization (PeI) source uses atoms of rare gases or molecules (N2) excited to give a flux of metastable atoms or molecules (A*) able by collision to ionize a target molecule (M) on the condition that the process is exothermic (i.e., IE(M) < EE(A)). As electron ionization, PeI allows the ionization of apolar species such as saturated hydrocarbons yielding molecular ions. In this work we present the application of vacuum PeI source coupled with a FT-ICR instrument for the characterization of a diesel fuel. Argon and krypton, as metastable gas, allow reducing significantly the fragmentation extent compared to electron ionization. Unlike with an atmospheric pressure source, the use of a vacuum source allows a good control of the ionization conditions with the absence of oxygen or other reactant such as water

Réchauffement climatique et morue de l'Atlantique

National audienceL'utilisation d'un nouveau modèle d'habitat a permis d'évaluer les changements passés et potentiels de la probabilité de présence de la morue en Atlantique nord, dans le contexte du réchauffement climatique. Les résultats montrent que les mouvements biogéographiques attendus varient en intensité et en vitesse selon la zone géographique considérée et le scénario climatique envisag