Matching Items (6)
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In many social mammals, females who form close, differentiated bonds with others experience greater offspring survival and longevity. We still know little, however, about how females' relationships are structured within the social group, or whether connections beyond the level of the dyad have any adaptive value. Here, we apply social

In many social mammals, females who form close, differentiated bonds with others experience greater offspring survival and longevity. We still know little, however, about how females' relationships are structured within the social group, or whether connections beyond the level of the dyad have any adaptive value. Here, we apply social network analysis to wild baboons in order to evaluate the comparative benefits of dyadic bonds against several network measures. Results suggest that females with strong dyadic bonds also showed high eigenvector centrality, a measure of the extent to which an individual's partners are connected to others in the network. Eigenvector centrality was a better predictor of offspring survival than dyadic bond strength. Previous results have shown that female baboons derive significant fitness benefits from forming close, stable bonds with several other females. Results presented here suggest that these benefits may be further augmented if a female's social partners are themselves well connected to others within the group rather than being restricted to a smaller clique.

ContributorsCheney, Dorothy L. (Author) / Silk, Joan (Author) / Seyfarth, Robert M. (Author) / College of Liberal Arts and Sciences (Contributor)
Created2016-07-27
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Chimpanzees confer benefits on group members, both in the wild and in captive populations. Experimental studies of how animals allocate resources can provide useful insights about the motivations underlying prosocial behavior, and understanding the relationship between task design and prosocial behavior provides an important foundation for future research exploring these

Chimpanzees confer benefits on group members, both in the wild and in captive populations. Experimental studies of how animals allocate resources can provide useful insights about the motivations underlying prosocial behavior, and understanding the relationship between task design and prosocial behavior provides an important foundation for future research exploring these animals' social preferences. A number of studies have been designed to assess chimpanzees' preferences for outcomes that benefit others (prosocial preferences), but these studies vary greatly in both the results obtained and the methods used, and in most cases employ procedures that reduce critical features of naturalistic social interactions, such as partner choice. The focus of the current study is on understanding the link between experimental methodology and prosocial behavior in captive chimpanzees, rather than on describing these animals' social motivations themselves. We introduce a task design that avoids isolating subjects and allows them to freely decide whether to participate in the experiment. We explore key elements of the methods utilized in previous experiments in an effort to evaluate two possibilities that have been offered to explain why different experimental designs produce different results: (a) chimpanzees are less likely to deliver food to others when they obtain food for themselves, and (b) evidence of prosociality may be obscured by more “complex” experimental apparatuses (e.g., those including more components or alternative choices). Our results suggest that the complexity of laboratory tasks may generate observed variation in prosocial behavior in laboratory experiments, and highlights the need for more naturalistic research designs while also providing one example of such a paradigm.

ContributorsHouse, Bailey R. (Author) / Silk, Joan (Author) / Lambeth, Susan P. (Author) / Schapiro, Steven J. (Author) / College of Liberal Arts and Sciences (Contributor)
Created2014-09-05
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Although vocal production in non-human primates is highly constrained, individuals appear to have some control over whether to call or remain silent. We investigated how contextual factors affect the production of grunts given by wild female chacma baboons, Papio ursinus, during social interactions. Females grunted as they approached other adult

Although vocal production in non-human primates is highly constrained, individuals appear to have some control over whether to call or remain silent. We investigated how contextual factors affect the production of grunts given by wild female chacma baboons, Papio ursinus, during social interactions. Females grunted as they approached other adult females 28% of the time. Supporting previous research, females were much more likely to grunt to mothers with young infants than to females without infants. Grunts also significantly increased the likelihood of affiliative interactions among all partners. Notably, however, grunts did not simply mirror existing social bonds. Instead, they appeared to perform a very different function: namely, to serve as signals of benign intent between partners whose relationship is not necessarily close or predictable. Females were less likely to grunt to their mothers or adult daughters—the individuals with whom they shared the closest and least aggressive bonds—than to other females. In contrast, patterns of grunting between sisters were similar to those between nonkin, perhaps reflecting sisters’ more ambivalent relationships. Females grunted at higher rates to lower-ranking, than to higher-ranking, females, supporting the hypothesis that grunts do not simply signal the signaler’s level of arousal or anxiety about receiving aggression, but instead function as signals of benign intent. Taken together, results suggest that the grunts given by female baboons serve to reduce uncertainty about the likely outcome of an interaction between partners whose relationship is not predictably affiliative. Despite their limited vocal repertoire, baboons appear to be skilled at modifying call production in different social contexts and for different audiences.

ContributorsSilk, Joan (Author) / Seyfarth, Robert M. (Author) / Cheney, Dorothy L. (Author) / College of Liberal Arts and Sciences (Contributor)
Created2016-10-26
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Sexually selected infanticide is an important source of infant mortality in many mammalian species. In species with long-term male-female associations, females may benefit from male protection against infanticidal outsiders. We tested whether mountain gorilla (Gorilla beringei beringei) mothers in single and multi-male groups monitored by the Dian Fossey Gorilla Fund’s

Sexually selected infanticide is an important source of infant mortality in many mammalian species. In species with long-term male-female associations, females may benefit from male protection against infanticidal outsiders. We tested whether mountain gorilla (Gorilla beringei beringei) mothers in single and multi-male groups monitored by the Dian Fossey Gorilla Fund’s Karisoke Research Center actively facilitated interactions between their infants and a potentially protective male. We also evaluated the criteria mothers in multi-male groups used to choose a preferred male social partner. In single male groups, where infanticide risk and paternity certainty are high, females with infants <1 year old spent more time near and affiliated more with males than females without young infants. In multi-male groups, where infanticide rates and paternity certainty are lower, mothers with new infants exhibited few behavioral changes toward males. The sole notable change was that females with young infants proportionally increased their time near males they previously spent little time near when compared to males they had previously preferred, perhaps to encourage paternity uncertainty and deter aggression. Rank was a much better predictor of females’ social partner choice than paternity. Older infants (2–3 years) in multi-male groups mirrored their mothers’ preferences for individual male social partners; 89% spent the most time in close proximity to the male their mother had spent the most time near when they were <1 year old. Observed discrepancies between female behavior in single and multi-male groups likely reflect different levels of postpartum intersexual conflict; in groups where paternity certainty and infanticide risk are both high, male-female interests align and females behave accordingly. This highlights the importance of considering individual and group-level variation when evaluating intersexual conflict across the reproductive cycle.

ContributorsRosenbaum, Stacy (Author) / Hirwa, Jean Paul (Author) / Silk, Joan (Author) / Vigilant, Linda (Author) / Stoinski, Tara S. (Author) / College of Liberal Arts and Sciences (Contributor)
Created2016-02-10
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Humans are seemingly unique among the great apes with regard to their monogamous mating behavior. Since chimpanzees (Pan troglodytes) are humans closest living relative, understanding their actions may give insight into the evolutionary development of certain behaviors. In this paper, the mating behavior of chimpanzees will be evaluated in hopes

Humans are seemingly unique among the great apes with regard to their monogamous mating behavior. Since chimpanzees (Pan troglodytes) are humans closest living relative, understanding their actions may give insight into the evolutionary development of certain behaviors. In this paper, the mating behavior of chimpanzees will be evaluated in hopes of better understanding any similarities or differences compared to that of humans. Wild male chimpanzees have shown to reject solicitations from females at full swelling. The hypothesis being tested was that a male chimpanzee will reject a female who solicits a mating event due to age, rank, and parity. Long term data from Gombe National Park in Tanzania, Africa was used to test this. As expected, parous females were less likely to be rejected than nulliparous females, rejection was more likely if several other swollen females were present, and rejection was less likely if the female was higher-ranking/older. Surprisingly, it was found that younger males were more likely to reject females than prime males were. This was most likely due to the fact that almost always, higher-ranking males were also present, which may have deterred young males from mating. The results also showed that there was no effect of male rank and female reproductive state on the probability of rejection. The findings of this study may help to show a potential evolutionary step towards conscious mate selection as seen in humans.
ContributorsTrenter, Kayla Ashley (Author) / Gilby, Ian (Thesis director) / Silk, Joan (Committee member) / School of Molecular Sciences (Contributor) / School of Human Evolution & Social Change (Contributor) / Department of English (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
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Exposure to social and ecological adversity during sensitive windows of development often leadto disadvantageous outcomes in adulthood such as reduced social connectedness and shorter lifespan. Consequences of early life adversity can persist across generations. The mother is a crucial component of the early life environment for mammals and plays an

Exposure to social and ecological adversity during sensitive windows of development often leadto disadvantageous outcomes in adulthood such as reduced social connectedness and shorter lifespan. Consequences of early life adversity can persist across generations. The mother is a crucial component of the early life environment for mammals and plays an important role in shaping offspring development. The mechanisms underlying the associations between early life adversity, adult outcomes, and transgenerational effects are not well established, and the complexities of how early life environments shape the ways offspring prioritize different dimensions of development are only beginning to be understood. This dissertation leverages longitudinal data, detailed behavioral observations, fecal hormone sampling, and noninvasive estimates of infant body size to assess how early life experiences shape development and adult outcomes in a wild population of olive baboons (Papio anubis) in Laikipia, Kenya. Four dissertation papers address: 1) the relationship between a mother’s early life adversity and her maternal effort, physiology, and offspring survival; 2) how the maternal environment shapes the ways developing offspring allocate resources among play, behavioral independence, and growth; 3) the role of interaction style in mediating the relationship between early life adversity and adult female sociability; and 4) the relative importance of female competition over food, mates, and male caretakers. Results of these papers show early life adversity can have lasting consequences on maternal effort and physiology, which in turn shape offspring developmental trajectories. Females who experienced early life adversity were less likely to develop an interaction style that was associated with sociability. Finally, the energetic costs of lactation were the primary driver of female competition, and in light of findings in chacma and yellow baboons, this indicates evolution has finely tuned female baboons’ responses to the social and ecological pressures of their local environments. To better understand the complexities of early life experiences and developmental trajectories, it is important to leverage longitudinal data and create comprehensive models of the maternal environment and infant development.
ContributorsPatterson, Sam K (Author) / Silk, Joan (Thesis advisor) / Hinde, Katie (Committee member) / Langergraber, Kevin (Committee member) / Arizona State University (Publisher)
Created2021