Abstract: Lateralization of emotions has received great attention in the last decades, both in humans and animals, but little interest has been given to side bias in perceptual processing. Here, we investigated the influence of the emotional valence of stimuli on visual and olfactory explorations by horses, a large mammalian species with two large monocular visual fields and almost complete decussation of optic fibres. We confronted 38 Arab mares to three objects with either a positive, negative or neutral emotional valence (novel object). The results revealed a gradient of exploration of the 3 objects according to their emotional value and a clear asymmetry in visual exploration. When exploring the novel object, mares used preferentially their right eyes, while they showed a slight tendency to use their left eyes for the negative object. No asymmetry was evidenced for the object with the positive valence. A trend for an asymmetry in olfactory investigation was also observed. Our data confirm the role of the left hemisphere in assessing novelty in horses like in many vertebrate species and the possible role of the right hemisphere in processing negative emotional responses. Our findings also suggest the importance of both hemispheres in the processing positive emotions. This study is, to our knowledge, the first to demonstrate clearly that the emotional valence of a stimulus induces a specific visual lateralization pattern.

Abstract: We studied the relationship of reciprocity, gender, and racial composition (Caucasian, African American, cross-race) of adolescent friendship dyads to similarity and proximity in 136 young adolescents. We found that adolescents selected friends who were of the same gender and race and that female dyads were more similar than male dyads on verbal achievement and several personality dimensions. Caucasian dyads were more similar than African American dyads on verbal achievement, mental alertness, and dominance. African American adolescents had more contact with their best friends outside school, whereas Caucasian adolescent friends had more in-school contact. African American students had fewer reciprocal relationships than the Caucasian students. Cross-race friendships were less reciprocal than same-race friendships. Race and gender were important in determining friendship patterns. Similarity and proximity were more important than reciprocity in understanding early adolescent friendships.

Abstract: The relationship between social behaviour and skin injuries (caused by horns) of loose housed horned cows was investigated on 35 dairy farms. While the frequencies of two agonistic behaviour elements (push and chase away) were positively correlated with the occurrence of skin injuries, the frequencies of butting and homing were not. Butting appears to have an ambivalent motivation, in that its occurrence is correlated positively both with agonistic behaviour and with social licking. Horning showed a positive correlation with social licking only. Four groups of husbandry conditions that may be associated with the occurrence of social behaviour and of injuries were distinguished: i) herd management, with variables including problem solving management by the farmer, integration of new cows, and dealing with periparturient and oestrus cows; ii) human-animal relationship, with variables including ability to identify individual cows, frequency of brushing the cows, number of milkers, and frequency of personnel changes; iii) animal characteristics, with the variable of herd size; and iv) stable characteristics, with the variable of space per cow (m2). The relevance of the husbandry variables investigated here had been confirmed in a previous stepwise regression analysis (Menke 1996). The variables for herd management and human-animal relationship conditions correlated in a consistent way with the occurrence of agonistic behaviour and/or of injuries, while most of them also correlated in the opposite direction with the occurrence of social licking. Herd size correlated positively with agonistic behaviour, but negatively with social licking. Space per cow correlated negatively with agonistic behaviour and injuries. In more than 70 per cent of the herds investigated, the levels of agonistic behaviour and of skin injuries were low, implying that horned dairy cows can be kept with less risk than is often assumed. We argue that such risks strongly depend on management factors that can be improved.

Abstract: Brain asymmetry—i.e. the specialisation of each cerebral hemisphere for sensorimotor processing mechanisms and for specific cognitive functions—is widely distributed among vertebrates. Several factors, such as embryological manipulations, sex, age, and breeds, can influence the maintenance, strength, and direction of laterality within a certain vertebrate species. Brain lateralisation is a universal phenomenon characterising not only cerebral control of cognitive or emotion-related functions but also cerebral regulation of somatic processes, and its evolution is strongly influenced by social selection pressure. Diseases are well known to be a cost of sociality but their role in influencing behaviour has received very little attention. The present study investigates the influence of illness conditions as a source of variation on laterality in a social keystone vertebrate predator model, the lion. In a preliminary stage, the clinical conditions of 24 adult lions were assessed. The same animals were scored for forelimb preference when in the quadrupedal standing position. Lions show a marked forelimb preference with a population bias towards the use of the right forelimb. Illness conditions strongly influenced the strength of laterality bias, with a significant difference between clinically healthy and sick lions. According to these results, health conditions should be recognised as an important source of variation in brain lateralisation.

Abstract: In animal groups, collective movements emerge from individual interactions. Biologists seek to identify how characteristics of actors in these groups, and their relationships, influence the decision-making process. We distinguished two basic factors determining leadership in group choices: identity and state. We hypothesized that identity is more important to leadership in groups with stable relationships, which permit the development of habitual roles. In groups with fluid membership, particular individuals or subgroups are less likely to emerge as consistent leaders. Instead, we predicted that movement initiation in unstable groups depends on individual state at the time of the decision. We characterized how identity and reproductive state influenced leadership patterns in the movements of plains zebra. As in many other mammals, lactation in this species significantly alters water and energy needs. We investigated leadership in tightly knit harems and loosely bonded herds of multiple harems. Harem females tended to have habitual roles in the initiation of harem movement. In herds, however, we found no consistent leaders among harems. At both levels of social organization, lactation was a key determinant of leadership. In harems, lactating females were more likely to initiate movement than nonlactating females. In turn, harems containing lactating females were more likely to lead herd movements. Thus, we conclude that social relationships and reproductive state together shape the interactions that produce group behaviours. One benefit to lactating females of leading herd movements is preferential access to scarce water. Thus, leadership roles in group decisions may have fitness consequences.