Abstract: To examine the nature of age-dependent cognitive decline, performance in terms of concurrent object discriminations was assessed in aged and nonaged Japanese monkeys (Macaca fuscata). Aged monkeys required more sessions and committed more errors than nonaged ones in the discriminations, even in simple object discriminations. Analyses of errors suggest that aged monkeys repeated the same errors and committed more errors when they chose a negative object at the 1st trial. A hypothesis analysis of behavior suggests that their incorrect choices were mainly due to object preference. Therefore, the impairment was probably caused by a failure to inhibit inappropriate responses. Together with previous neuropsychological findings, deficits of aged monkeys in the performance of object discriminations can be explained by dysfunction of the frontal cortex.

Abstract: BACKGROUND: Psychopathologies such as anxiety- and depression-related disorders are often characterized by impaired social behaviours including excessive aggression and violence. Excessive aggression and violence likely develop as a consequence of generally disturbed emotional regulation, such as abnormally high or low levels of anxiety. This suggests an overlap between brain circuitries and neurochemical systems regulating aggression and anxiety. In this review, we will discuss different forms of male aggression, rodent models of excessive aggression, and neurobiological mechanisms underlying male aggression in the context of anxiety. We will summarize our attempts to establish an animal model of high and abnormal aggression using rats selected for high (HAB) versus low (LAB) anxiety-related behaviour. Briefly, male LAB rats and, to a lesser extent, male HAB rats show high and abnormal forms of aggression compared with non-selected (NAB) rats, making them a suitable animal model for studying excessive aggression in the context of extremes in innate anxiety. In addition, we will discuss differences in the activity of the hypothalamic-pituitary-adrenal axis, brain arginine vasopressin, and the serotonin systems, among others, which contribute to the distinct behavioural phenotypes related to aggression and anxiety. Further investigation of the neurobiological systems in animals with distinct anxiety phenotypes might provide valuable information about the link between excessive aggression and disturbed emotional regulation, which is essential for understanding the social and emotional deficits that are characteristic of many human psychiatric disorders.

Abstract: Close associations between adult males and lactating females and their dependent infants are not commonly described in non-monogamous mammals. However, such associations [sometimes called friendships (Smuts 1985)] are regularly observed in several primate species in which females mate with multiple males during the fertile period. The absence of mating exclusivity among friends suggests that males should invest little in infant care, raising questions about the adaptive significance of friendship bonds. Using data from genetic paternity analyses, patterns of behavior, and long-term demographic and reproductive records, we evaluated the extent to which friendships in four multi-male, multi-female yellow baboon (Papio cynocephalus) groups in Amboseli, Kenya represent joint parental care of offspring or male mating effort. We found evidence that mothers and infants benefited directly from friendships; friendships provided mother–infant dyads protection from harassment from other adult and immature females. In addition, nearly half of all male friends were the genetic fathers of offspring and had been observed mating with mothers during the days of most likely conception for those offspring. In contrast, nearly all friends who were not fathers were also not observed to consort with the mother during the days of most likely conception, suggesting that friendships between mothers and non-fathers did not result from paternity confusion. Finally, we found no evidence that prior friendship increased a male’s chances of mating with a female in future reproductive cycles. Our results suggest that, for many male–female pairs at Amboseli, friendships represented a form of biparental care of offspring. Males in the remaining friendship dyads may be trading protection of infants in exchange for some resources or services not yet identified. Our study is the first to find evidence that female primates gain social benefits from their early associations with adult males.

Abstract: This review highlights two areas of particular interest in the study of social learning in fowl. First, the role of social learning in the development of feeding and foraging behavior in young chicks and older birds is described. The role of the hen as a demonstrator and possible teacher is considered, and the subsequent social influence of brood mates and other companions on food avoidance and food preference learning is discussed. Second, the way in which work on domestic fowl has contributed to an understanding of the importance of directed social learning is examined. The well-characterized hierarchical social organization of small chicken flocks has been used to design studies which demonstrate that the probability of social transmission is strongly influenced by social relationships between birds. The practical implications of understanding the role of social learning in the spread of injurious behaviors in this economically important species are briefly considered.

Abstract: The formation of collaborating pairs by individuals belonging to two different classes occurs in the contexts of reproduction and intea-specific cooperation as well as of inter-specific mutualism. There is potential for partner choice and for competition for access to preferred partners in all three contexts. These selective forces have long been recognised as important in sexual selection, but their impact is not yet appreciated in cooperative and mutualistic systems. The formation of partnerships between members of different classes has much in common with the conclusion of trade agreements in human markets with two classes of traders, like producers and consumers, or employers and employees. Similar game-theoretical models can be used to predict the behaviour of rational traders in human markets and the evolutionarily stable strategies used in biological markets. We present a formal model in which the influence of the market mechanism on selection is made explicit. We restrict ourselves to biological markets in which: (1) Individuals do not compete over access to partners in an agonistic manner, but rather by outcompeting each other in those aspects that are preferred by the choosing party. (2) The commodity the partner has to offer cannot be obtained by the use of force, but requires the consent of the partner. These two restrictions ensure a dominant role for partner choice in the formation of partnerships. In a biological market model the decision to cooperate is based on the comparison between the offers of several potential partners, rather than on the behaviour of a single potential partner, as is implicitly assumed in currently accepted models of cooperation. In our example the members of one class A offer a commodity of fixed value in exchange for a commodity of variable value supplied by the other class, B. We show that when the B-class outnumbers the A-class sufficiently and the cost for the A-class to sample the offers of the B-class are low, the choosiness of the A-class will lead to selection for the supply of high value commodities by the B-class (Fig. 3a). Under the same market conditions, but with a high sampling cost this may still be the evolutionariy stable outcome, but another pair of strategies proves to be stable too: relaxed choosiness of class A coupled with low value commodities supplied by class B (Fig. 3b). We give a number of examples of mating, cooperative and mutualistic markets that resemble the low sampling cost situation depicted in Fig. 3a.