Abstract: Coordination of primate group movements by individual group members is generally categorized as leadership behavior, which entails several steps: deciding where to move next, initiating travel, and leading a group between food, water sources, and rest sites. Presumably, leaders are able to influence their daily foraging efficiency and nutritional intake, which could influence an individual's feeding ecology and long-term reproductive success. Within anthropoid species, females lead group movements in most female-bonded groups, while males lead groups in most nonfemale-bonded groups. Group leadership has not been described for social prosimians, which are typically not female-bonded. We describe group movements in two nonfemale-bonded, lemurid species living in southeastern Madagascar, Propithecus diadema edwardsi and Eulemur fulvus rufus. Although several social lemurids exhibit female dominance Eulemur fulvus rufus does not, and evidence for female dominance is equivocal in Propithecus diadema edwardsi. Given the ecological stresses that females face during reproduction, we predict that females in these two species will implement alternative behavioral strategies such as group leadership in conjunction with, or in the absence of, dominance interactions to improve access to food. We found that females in both species initiated and led group movements significantly more often than males did. In groups with multiple females, one female was primarily responsible for initiating and leading group movements. We conclude that female nutritional needs may determine ranging behavior to a large extent in these prosimian species, at least during months of gestation and lactation.

Abstract: Demonstrating the ability to ‘copy’ the behavior of others is an important aspect in determining whether social learning occurs and whether group level differences in a given behavior represent cultural differences or not. Understanding the occurrence of this process in its natural context is essential, but can be a daunting task in the wild. In order to test the social learning hypothesis for the acquisition of leaf swallowing (LS), a self-medicative behavior associated with the expulsion of parasites, we conducted semi-naturalistic experiments on two captive groups of parasite-free, naïve chimpanzees (Pan troglodytes). Individuals in the group were systematically provided appropriate stimuli (rough hispid leaves) identical to those used by chimpanzees in the wild. Individuals initially responded in a variety of ways, ranging from total aversion to normal chewing and swallowing. Over time, however, the two groups adopted different variants for inserting and folding the leaves in the mouth prior to swallowing them (complete and partial LS), following the specific method spontaneously displayed by the first and primary LS models in their respective groups. These variants were similar to LS displayed by chimpanzees in the wild. Using the option-bias method, we found evidence for social learning leading to group-level biased transmission and group-level stabilization of these two variants. This is the first report on two distinct cultural variants innovated in response to the introduction of natural stimuli that emerged and spread spontaneously and concurrently within two adjacent groups of socially housed primates. These observations support the assertion that LS may reflect a generalized propensity for ingesting rough hispid leaves, which can be socially induced and transmitted within a group. Ingesting an adequate number of these leaves induces increased gut motility, which is responsible for the subsequent expulsion of particular parasite species in the wild. Cultural transmission and maintenance of LS within a group and associative learning by the individual of the positive consequences of this otherwise non-nutritive mode of ingestion is proposed to be the pivotal link between this feeding propensity and its maintenance as a self-medicative behavior by great apes in the wild.

Abstract: Altruism poses a problem for evolutionary biologists because natural selection is not expected to favor behaviors that are beneficial to recipients, but costly to actors. The theory of kin selection, first articulated by Hamilton (1964), provides a solution to the problem. Hamilton's well-known rule (br > c) provides a simple algorithm for the evolution of altruism via kin selection. Because kin recognition is a crucial requirement of kin selection, it is important to know whether and how primates can recognize their relatives. While conventional wisdom has been that primates can recognize maternal kin, but not paternal kin, this view is being challenged by new findings. The ability to recognize kin implies that kin selection may shape altruistic behavior in primate groups. I focus on two cases in which kin selection is tightly woven into the fabric of social life. For female baboons, macaques, and vervets maternal kinship is an important axis of social networks, coalitionary activity, and dominance relationships. Detailed studies of the patterning of altruistic interactions within these species illustrate the extent and limits of nepotism in their social lives. Carefully integrated analyses of behavior, demography, and genetics among red howlers provide an independent example of how kin selection shapes social organization and behavior. In red howlers, kin bonds shape the life histories and reproductive performance of both males and female. The two cases demonstrate that kin selection can be a powerful source of altruistic activity within primate groups. However, to fully assess the role of kin selection in primate groups, we need more information about the effects of kinship on the patterning of behavior across the Primates and accurate information about paternal kin relationships.

Abstract: Great ape gesture has become a research topic of intense interest, because its intentionality and flexibility suggest strong parallels to human communication. Yet the fundamental question of whether an animal species’ gestures carry specific meanings has hardly been addressed. We set out a systematic approach to studying intentional meaning in the gestural communication of non-humans and apply it to a sample of orangutan gestures. We propose that analysis of meaning should be limited to gestures for which (1) there is strong evidence for intentional production and (2) the recipient’s final reaction matches the presumed goal of the signaller, as determined independently. This produces a set of successful instances of gesture use, which we describe as having goal–outcome matches. In this study, 28 orangutans in three European zoos were observed for 9 months. We distinguished 64 gestures on structural grounds, 40 of which had frequent goal–outcome matches and could therefore be analysed for meaning. These 40 gestures were used predictably to achieve one of 6 social goals: to initiate an affiliative interaction (contact, grooming, or play), request objects, share objects, instigate co-locomotion, cause the partner to move back, or stop an action. Twenty-nine of these gestures were used consistently with a single meaning. We tested our analysis of gesture meaning by examining what gesturers did when the response to their gesture did not match the gesture’s meaning. Subsequent actions of the gesturer were consistent with our assignments of meaning to gestures. We suggest that, despite their contextual flexibility, orangutan gestures are made with the expectation of specific behavioural responses and thus have intentional meanings as well as functional consequences.

Abstract: Place learning abilities represent adaptations that contribute also to foraging efficiency under given spatio-temporal conditions. We investigated if this ability in turn constrains decision making in two sympatric vole species: while the herbivorous common vole (Microtus arvalis) feeds on spatio-temporally predictable food resources (e.g. roots, tubers and shoots of plant tubers), the omnivorous bank vole (Myodes glareolus) additionally subsists on temporally unpredictable food resources (e.g. insects and seeds). Here, we compare the spatial reference memory and working memory of the two species. In an automated operant home cage with eight water places, female voles either had to learn the fixed position of non-depletable places (reference memory task) or learn and avoid previously visited water places depleted in a single visit (win-shift task). In the reference memory task, Microtus females required significantly more choices to find all water places, initially performed slightly worse than Myodes females, and displayed slightly lower asymptotic performance. Both species were highly similar in new learning of the same task. In the more complex win-shift task, asymptotic performance was significantly lower in Microtus (72% correct) than in Myodes (79%). Our results suggest that both vole species resemble each other in their efficiency to exploit habitats with low spatio-temporal complexity but may differ in their efficiency at exploiting habitats with temporally changing spatial food distributions. The results imply that spatial ability adjusted to specific food distributions may impair flexible use of habitats that differ in their food distribution and therefore, decrease a species’ chances of survival in highly dynamic environments.