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Waeber P.O., & Hemelrijk C.K. (2003). Female Dominance and Social Structure in Alaotran Gentle Lemurs. Behaviour, 140(10), 1235–1246.
Abstract: Abstract:
Lemur social systems have the striking social feature, that adult females consistently evoke submissive behaviour of adult males. In the Alaotran gentle lemur, Hapalemur griseus alaotrensis, however, female dominance has not been studied yet. Here we confirm female dominance over males on the basis of a 5-month field study of the social behaviour of four groups, in the Lake Alaotra marshland of eastern Madagascar. Further, we found that dominant individuals initiated aggressive interactions significantly more often than lowerranking ones, they initiated group movements more often and higher-ranking individuals were groomed more often. The spatial configuration was remarkable, since individuals were closer in space to those more distant in rank.
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Van Doorn G.S., Hengeveld G.M., & Weissing F.J. (2003). The Evolution of Social Dominance I: Two-player Models. Behavior, 140(10), 1305–1332.
Abstract: A difference in dominance rank is an often-used cue to resolve conflicts between two animals without escalated fights. At the group level, adherence to a dominance convention efficiently reduces the costs associated with conflicts, but from an individual's point of view, it is difficult to explain why a low ranking individual should accept its subordinate status. This is especially true if, as suggested by several authors, dominance not necessarily reflects differences in fighting ability but rather results from arbitrary historical asymmetries. According to this idea, rank differentiation emerges from behavioural strategies, referred to as winner and loser effects, in which winners of previous conflicts are more likely to win the current conflict, whereas the losers of previous conflicts are less likely to do so. In order to investigate whether dominance, based on such winner and loser effects, can be evolutionarily stable, we analyse a game theoretical model. The model focuses on an extreme case in which there are no differences in fighting ability between individuals at all. The only asymmetries that may arise between individuals are generated by the outcome of previous conflicts. By means of numerical analysis, we find alternative evolutionarily stable strategies, which all utilize these asymmetries for conventional conflict resolution. One class of these strategies is based on winner and loser effects, thus generating evolutionarily stable dominance relations even in the absence of differences in resource holding potential.
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McGuigan, M. P., & Wilson, A. M. (2003). The effect of gait and digital flexor muscle activation on limb compliance in the forelimb of the horse Equus caballus. J Exp Biol, 206(Pt 8), 1325–1336.
Abstract: A horse's legs are compressed during the stance phase, storing and then returning elastic strain energy in spring-like muscle-tendon units. The arrangement of the muscle-tendon units around the lever-like joints means that as the leg shortens the muscle-tendon units are stretched. The forelimb anatomy means that the leg can be conceptually divided into two springs: the proximal spring, from the scapula to the elbow, and the distal spring, from the elbow to the foot. In this paper we report the results of a series of experiments testing the hypothesis that there is minimal scope for muscle contraction in either spring to adjust limb compliance. Firstly, we demonstrate that the distal, passive leg spring changes length by 127 mm (range 106-128 mm) at gallop and the proximal spring by 12 mm (9-15 mm). Secondly, we demonstrate that there is a linear relationship between limb force and metacarpo-phalangeal (MCP) joint angle that is minimally influenced by digital flexor muscle activation in vitro or as a function of gait in vivo. Finally, we determined the relationship between MCP joint angle and vertical ground-reaction force at trot and then predicted the forelimb peak vertical ground-reaction force during a 12 m s(-1) gallop on a treadmill. These were 12.79 N kg(-1) body mass (BM) (range 12.07-13.73 N kg(-1) BM) for the lead forelimb and 15.23 N kg(-1) BM (13.51-17.10 N kg(-1) BM) for the non-lead forelimb.
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Van Doorn G.S., Hengeveld G.M., & Weissing F.J. (2003). The Evolution of Social Dominance II: Multi-Player Models. Behavior, 140(10), 1333–1358.
Abstract: The social hierarchies observed in natural systems often show a high degree of transitivity. Transitive hierarchies do not only require rank differentiation within pairs of individuals but also a higher level ordering of relations within the group. Several authors have suggested that the formation of linear hierarchies at the group level is an emergent property of individual behavioural rules, referred to as winner and loser effects. Winner and loser effects occur if winners of previous conflicts are more likely to escalate the current conflict, whereas the losers of previous conflicts are less likely to do so. According to this idea, an individual's position in a hierarchy may not necessarily reflect its fighting ability, but may rather result from arbitrary historical asymmetries, in particular the history of victories and defeats. However, if this is the case, it is difficult to explain from an evolutionary perspective why a low ranking individual should accept its subordinate status. Here we present a game theoretical model to investigate whether winner and loser effects giving rise to transitive hierarchies can evolve and under which conditions they are evolutionarily stable. The main version of the model focuses on an extreme case in which there are no intrinsic differences in fighting ability between individuals. The only asymmetries that may arise between individuals are generated by the outcome of previous conflicts. We show that, at evolutionary equilibrium, these asymmetries can be utilized for conventional conflict resolution. Several evolutionarily stable strategies are based on winner and loser effects and these strategies give rise to transitive hierarchies.
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Wittig, R. M., & Boesch, C. (2003). The Choice of Post-conflict Interactions in Wild Chimpanzees (Pan troglodytes). Behaviour, 140(11), 1527–1559.
Abstract: Some costs of conflicts remain after an aggressive interaction has been terminated. Postconflict management in social living animals can reduce those costs by means of a variety of interactions implemented after aggression (e.g.reconciliation, consolation, redirected aggression). Each post-conflict interaction (PCI) provides different advantages and disadvantages, although the functions may sometimes overlap. Individuals can therefore choose a PCI to achieve the most favourable outcome within a given conflict situation. We examined 876 dyadic aggressive interactions among 18 wild chimpanzees (Pan troglodytes verus) of both sexes in the Tai National Park, Céte d'Ivoire. We investigated which conflict-condition led to which type of PCI and related the choice of PCI to its advantages and disadvantages. Tai chimpanzees used reconciliation to resolve conflicts among high value partners and when approaching the former opponent was unlikely to entail further aggression. Consolation seemed to substitute for reconciliation, when were opponents low value partners or approaching the former opponent was too risky, such as when further aggression was likely. Tai chimpanzees renewed aggression after undecided conflicts and when losers were unexpected. They used redirected aggression after long conflicts, possibly because friendly PCIs were likely to fail. However, Tai chimpanzees continued with business as usual when conflicts were very short, and they avoided further interactions when the accessibility of the resource was unlimited. Tai chimpanzees appeared to follow a clear-cut evaluation process as they seemed to weigh advantages against disadvantages for the appropriate choice of PCI.
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Milgram, N. W. (2003). Cognitive Experience and Its Effect on Age-Dependent Cognitive Decline in Beagle Dogs. Neurochemical Research, 28(11), 1677–1682.
Abstract: Test-sophisticated beagle dogs show marked age sensitivity in a size discrimination learning task, with old and senior dogs performing significantly more poorly than young dogs. By contrast, age differences in learning were not seen in dogs naive with respect to neuropsychological test experience. These results indicate that old animals benefit less from prior cognitive experience than young animals, which is an example of an age-dependent loss in plasticity. This finding also suggests that behaviorally experienced animals are a more useful model of human cognitive aging than behaviorally naive animals. We also looked at the effect of a program of behavioral enrichment in aged dogs. One year of enrichment did not lead to significant differences, but after 2 years the behaviorally enriched group performed significantly better than the control group. The effect after 2 years indicates that a prolonged program of cognitive enrichment can serve as an effective intervention in aged dogs. These findings demonstrate that cognitive abilities in aged animals can be modified by providing behavioral experience, indicating that cognitive abilities remain moderately plastic, even in very old animals.
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Hall, C. A., Cassaday, H. J., & Derrington, A. M. (2003). The effect of stimulus height on visual discrimination in horses. J. Anim Sci., 81(7), 1715–1720.
Abstract: This study investigated the effect of stimulus height on the ability of horses to learn a simple visual discrimination task. Eight horses were trained to perform a two-choice, black/white discrimination with stimuli presented at one of two heights: ground level or at a height of 70 cm from the ground. The height at which the stimuli were presented was alternated from one session to the next. All trials within a single session were presented at the same height. The criterion for learning was four consecutive sessions of 70% correct responses. Performance was found to be better when stimuli were presented at ground level with respect to the number of trials taken to reach the criterion (P < 0.05), percentage of correct first choices (P < 0.01), and repeated errors made (P < 0.01). Thus, training horses to carry out tasks of visual discrimination could be enhanced by placing the stimuli on the ground. In addition, the results of the present study suggest that the visual appearance of ground surfaces is an important factor in both horse management and training.
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Gulotta, M., Rogatsky, E., Callender, R. H., & Dyer, R. B. (2003). Primary folding dynamics of sperm whale apomyoglobin: core formation. Biophys J, 84(3), 1909–1918.
Abstract: The structure, thermodynamics, and kinetics of heat-induced unfolding of sperm whale apomyoglobin core formation have been studied. The most rudimentary core is formed at pH(*) 3.0 and up to 60 mM NaCl. Steady state for ultraviolet circular dichroism and fluorescence melting studies indicate that the core in this acid-destabilized state consists of a heterogeneous composition of structures of approximately 26 residues, two-thirds of the number involved for horse heart apomyoglobin under these conditions. Fluorescence temperature-jump relaxation studies show that there is only one process involved in Trp burial. This occurs in 20 micro s for a 7 degrees jump to 52 degrees C, which is close to the limits placed by diffusion on folding reactions. However, infrared temperature jump studies monitoring native helix burial are biexponential with times of 5 micro s and 56 micro s for a similar temperature jump. Both fluorescence and infrared fast phases are energetically favorable but the slow infrared absorbance phase is highly temperature-dependent, indicating a substantial enthalpic barrier for this process. The kinetics are best understood by a multiple-pathway kinetics model. The rapid phases likely represent direct burial of one or both of the Trp residues and parts of the G- and H-helices. We attribute the slow phase to burial and subsequent rearrangement of a misformed core or to a collapse having a high energy barrier wherein both Trps are solvent-exposed.
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Mettke-Hofmann, C., & Gwinner, E. (2003). Long-term memory for a life on the move. Proc. Natl. Acad. Sci. U.S.A., 100(10), 5863–5866.
Abstract: Evidence is accumulating that cognitive abilities are shaped by the specific ecological conditions to which animals are exposed. Long-distance migratory birds may provide a striking example of this. Field observations have shown that, at least in some species, a substantial proportion of individuals return to the same breeding, wintering, and stopover sites in successive years. This observation suggests that migrants have evolved special cognitive abilities that enable them to accomplish these feats. Here we show that memory of a particular feeding site persisted for at least 12 months in a long-distance migrant, whereas a closely related nonmigrant could remember such a site for only 2 weeks. Thus, it seems that the migratory lifestyle has influenced the learning and memorizing capacities of migratory birds. These results build a bridge between field observations suggesting special memorization feats of migratory birds and previous neuroanatomical results from the same two species indicating an increase in relative hippocampal size from the first to the second year of life in the migrant but not in the nonmigrant.
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Tang, A. C., Reeb, B. C., Romeo, R. D., & McEwen, B. S. (2003). Modification of Social Memory, Hypothalamic-Pituitary-Adrenal Axis, and Brain Asymmetry by Neonatal Novelty Exposure. The Journal of Neuroscience, 23(23), 8254–8260.
Abstract: Although corticosterone (a stress hormone) is known to influence social behavior and memory processes, little has been explored concerning its modulatory role in social recognition. In rats, social recognition memory for conspecifics typically lasts <2 hr when evaluated using a habituation paradigm. Using neonatal novelty exposure, a brief and transient early life stimulation method known to produce long-lasting changes in the hypothalamic-pituitary-adrenal axis, we found that social recognition memory was prolonged to at least 24 hr during adulthood. This prolonged social memory was paralleled by a reduction in the basal blood concentration of corticosterone. The same neonatal stimulation also resulted in a functional asymmetry expressed as a greater right-turn preference in a novel environment. Rats that preferred to turn right showed better social recognition memory. These inter-related changes in basal blood corticosterone concentration, turning asymmetry, and social recognition memory suggest that stress hormones and brain asymmetry are likely candidates for modulating social memory. Furthermore, given that neonatal stimulation has been shown to improve learning and memory performance primarily under aversive learning situations, the neonatal novelty exposure-induced enhancement in social recognition broadens the impact of early life stimulation to include the social domain.
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