Communication and Travel Coordination in Wild Bonobos

Group movement is often governed by simple, decentralized rules. From swarming locusts to crowds of commuters, self-organization often eliminates the need for a more explicit form of coordination. Passive, local cues, however, cannot explain group movement in many circumstances, especially among populations exhibiting low spatial cohesion and highly differentiated social relationships. The research presented in this dissertation examines communication and travel patterns of wild bonobos (Pan paniscus), a species of great ape with a highly fluid ‘fission-fusion’ social structure, in which individuals from a single social group regularly divide into smaller subgroups (‘parties’). In Chapters 1 and 2, we investigate the long-distance vocalizations that bonobos use to communicate between separated parties. We find that call combinations, but not single call types alone, were associated with particular patterns of inter-party movement. Specifically, individuals who were highly motivated to approach and join another party produced ‘whistle-high hoot’ combinations, while individuals motivated to recruit others to their own party produced distinct ‘low hoot-high hoot’ combinations. In Chapter 3, we turn our focus to ‘branch drag’ displays, a form of within-party communication. Bonobos performed these displays before traveling to distant feeding trees, but not prior to shorter bouts of travel, thus potentially providing individuals with information about subsequent group movement. Results from all three chapters demonstrate that bonobos use particular signals to facilitate movement patterns that are typical of fission-fusion societies. Furthermore, we suggest that the unpredictable nature of such a social structure may have favored individuals who are able to flexibly produce signals related to movement in order decrease the uncertainty associated with fission-fusion dynamics, and thereby reduce the costs of group coordination

The Cost of Living in Poverty: Long-Term Effects of Allostatic Load on Working Memory

Compared to their middle-income peers, adolescents reared in poverty perform less accurately on neurocognitive tasks. Previous research has not delineated an underlying mechanism that would account for these deficits in cognition. Allostatic load is a likely contributor as physiological stress in the brain disrupts neurogenesis, decreases the connections between dendrites, and induces atrophy in areas essential for working memory. The interplay between poverty, allostatic load, and working memory has not been previously studied. The current investigation examines the influence of cumulative, physiological "wear and tear" (at ages 9 and 13) on working memory functioning (at age 17), in a low- and middle-income sample (N= 68 and 102 per group, respectively). As predicted, proportion of life spent in poverty was inversely related to working memory functioning, with decreased accuracy for individuals living in persistent poverty. This pathway was fully mediated by increased allostatic load in childhood and early adolescence. These findings have implications for future health and education policies, and have provided preliminary evidence for the role of allostatic load on neurocognitive functioning

Partial Information Decomposition via Deficiency for Multivariate Gaussians

Bivariate partial information decompositions (PIDs) characterize how the information in a "message" random variable is decomposed between two "constituent" random variables in terms of unique, redundant and synergistic information components. These components are a function of the joint distribution of the three variables, and are typically defined using an optimization over the space of all possible joint distributions. This makes it computationally challenging to compute PIDs in practice and restricts their use to low-dimensional random vectors. To ease this burden, we consider the case of jointly Gaussian random vectors in this paper. This case was previously examined by Barrett (2015), who showed that certain operationally well-motivated PIDs reduce to a closed form expression for scalar messages. Here, we show that Barrett's result does not extend to vector messages in general, and characterize the set of multivariate Gaussian distributions that reduce to closed-form. Then, for all other multivariate Gaussian distributions, we propose a convex optimization framework for approximately computing a specific PID definition based on the statistical concept of deficiency. Using simplifying assumptions specific to the Gaussian case, we provide an efficient algorithm to approximately compute the bivariate PID for multivariate Gaussian variables with tens or even hundreds of dimensions. We also theoretically and empirically justify the goodness of this approximation.Comment: Presented at ISIT 2022. This version has been updated to reflect the final conference publication, including appendices. It also corrects technical errors in Remark 1 and Appendix C, adds a new experiment, and has a substantially improved presentation as well as additional detail in the appendix, compared to the previous arxiv versio

Cross-population variation in usage of a call combination: evidence of signal usage flexibility in wild bonobos

The arbitrary relationship between signifier and signified is one of the features responsible for language’s extreme lability, adaptability, and expressiveness. Understanding this arbitrariness and its emergence is essential in any account of the evolution of language. To shed light on the phylogeny of the phenomenon, comparative data examining the relationship between signal form and function in the communication systems of non-humans is central. Here we report the results of a study on the production and usage the whistle-high hoot call combination (W + HH) from two distant populations of wild bonobos (Pan paniscus): Lui Kotale, DRC, and Kokolopori, DRC. We find that the context in which bonobos produce the W + HHs varies systematically between populations. Our results suggest that variation in W + HH production may represent an example of signal-adjustment optionality, a key component of arbitrariness