Due to high levels of exploitation, habitat loss and habitat degradation, Pan troglodytes has experienced such a significant population reduction over the past 20 to 30 years that it is now on the IUCN (International Union for the Conservation of Nature and Natural Resources) Red List of Endangered Species. The Nigerian chimpanzee, Pan troglodytes ellioti (Gray 1862), is the most endangered of the four subspecies of chimpanzee. It has the smallest distribution and smallest population size, estimated in 2011 to be between 3,500 – 9,000 individuals. P. t. ellioti was first recognized as a distinct subspecies in 1997, and in 2008 an Action Plan Study Group was set up with the goal to determine the priority sites for its conservation and the actions that should be taken to ensure its long-term survival. The Action Plan was published in 2011 and this thesis is timely as it begins to answer some of the questions deemed important in the action plan. The overall aim of this study was to explore the ecology and behaviour of a small, isolated montane population of P. t. ellioti with the aim of making a useful contribution to future recommendations for the management and conservation of this subspecies. Specifically, I estimated the density of chimpanzees in Ngel Nyaki Forest Reserve, Taraba State, Nigeria and investigated their nesting ecology, elementary technology, diet, seed dispersal and the viability of seeds dispersed by the chimpanzees. I estimated chimpanzee density by using a combination of direct (direct observation) and indirect methods using nest counts. My investigation of nesting ecology concentrated on identifying habitat variables that influenced choice of nesting site. I assessed elementary technology by locating and describing both manufactured artefacts and unmanufactured objects, and I then located evidence from the surrounding environment to establish details about their presence or absence. Chimpanzee diet was assessed using evidence from faecal samples and artefacts. In order to identify preferences and agents involved in removal of various seed species ingested and dispersed by chimpanzees I set-up a series of experiments using plots into which seed piles were added. Lastly, I compared the rate of germination of conspecific seeds which had been passed through a chimpanzee gut with those that had not been dispersed.

When considering the array of terrestrial locomotor behaviors, bipedalism is a particularly rare way of moving about the landscape. In fact, humans are the only obligate terrestrial mammalian bipeds. Therefore, understanding both how and why it evolved is particularly intriguing. However, there is debate over why the evolution of bipedalism occurred and there is a large gap in knowledge for the mechanisms that underpin the evolution of these adaptive morphologies. One complicating factor for sorting out which models best explain how our hominin ancestors became bipedal is that they all rely on the same set of traits. Moreover, many of the traits that are thought to be diagnostic of bipedalism are only linked by association and have not been experimentally tested. That is, they do not appear in non-human primates and other quadrupeds. Therefore, addressing why the evolution of bipedalism occurred requires understanding the adaptive significance of traits linked with bipedalism. In this dissertation, I use an experimental approach employing both human and animal models to explore links between morphology and behavior and to tease apart the adaptive significance of particular traits. For the human portion of the dissertation, I use an inverse dynamics approach (estimating muscle forces from kinematic, kinetic, and anatomical data) to determine how modern human anatomy functions while walking using ape-like postures to clarify the links between morphology and energy costs in different mechanical regimes to determine the adaptive significance of postcranial anatomy. The results from this portion of the dissertation suggest that adopting different joint postures results in higher energy costs in humans due to an increase in active muscle volumes at the knee. These results lead to two conclusions important for understanding the evolution of human bipedalism. One is that human anatomy maintains low energy costs of walking in humans compared to chimpanzees regardless of lower limb postures. Second, the results suggest that erect trunk posture may be an important factor in reducing energy costs, therefore indicating that lumbar lordosis (the curvature of the lower spine) is important for reducing costs. For the animal portion of the dissertation, I use rats as a model for the quadrupedal-to-bipedal transition and experimentally induce bipedal posture and locomotion under a variety of loading conditions to determine if traits consistent with the evolution of bipedalism occur and under what conditions. This experimental design also has the ability to determine if there is a role for developmental plasticity in generating bipedal morphology to help answer the question how the evolution of bipedalism occurred. I find that inducing bipedal behaviors in a quadrupedal animal generates morphology consistent with human bipedal traits and that loading conditions have specific effects in different skeletal elements and at particular joints. I also find that there is a plausible role for developmental plasticity in generating adaptive bipedal morphology in the earliest hominins. Overall, the results from the experimental procedures in this dissertation were able to clarify links between behavior and bipedal morphology, demonstrate a plausible role for developmental plasticity in early adaptation to bipedal behavior in australopiths, determine the adaptive significance of human postcranial anatomy, and the ways in which postcranial anatomy reduces costs.

This thesis aimed to address two main questions. First, considering that personality is frequently associated with cognitive abilities in humans, do chimpanzees’ personalities and cognitive capacities covary in ways similar to what is observed in humans, as well as older evolutionary cousins, rhesus macaques? Second, given that human and animal personality have previously been shown to relate to health and longevity, does personality in chimpanzees also relate to various measures of health? Chapter 1 provides an introduction to and brief history of comparative personality psychology, particularly in the context of intelligence research and psychosomatic medicine. Chapter 2 describes three studies with a group of 19 zoo-housed chimpanzees who interacted with touchscreen tasks over the course of 3 years of research. We found that high Conscientious chimpanzees were more likely to stick with the tasks, and performed better as a results, but once their extra experience was taken into account, their performance advantage disappeared. However, we also found associations between better interest and performance with high Openness, high Extraversion, and low Agreeableness. In Chapter 3 we examine performance in conjunction with personality, with 9 rhesus macaques. The macaques also engaged with touchscreen tasks, but were expert subjects and displayed plateau performance. We found consistent associations between many measures of performance and both high Openness and high Friendliness (which is similar to Extraversion). With Chapter 4 we transition to our studies of personality and health. Chapter 4 examines personality and longevity in a sample of 538 personality rated, captive chimpanzees. These chimpanzees were followed for between 6 and 23 years after being rated. We found that high Agreeableness chimpanzees were more likely to live longer, but no other personality traits had a significant impact on longevity. In Chapter 5, we compared biomarkers from samples of 177 chimpanzees housed at the Yerkes National Primate Research Centre, and 29,314 humans from the National Health and Nutrition Examination Survey. Both samples had been tested for the most common haematological and metabolic blood biomarkers, and we used these to assess stress in the form of allostatic load, between species. We found a similar structure of biomarkers in across humans and chimpanzees. In Chapter 6, we took our allostatic load measure from chapter 5 and looked at how it was associated with personality, in the same chimpanzee sample from the Yerkes Primate Centre, and in the longitudinal Midlife in the United States and Midlife in Japan biomarker study samples, which consisted of 993 and 382 individuals, respectively. We found that Agreeableness was associated with allostatic load in both human samples, whereas Dominance was associated with allostatic load in chimpanzees. Finally, Chapter 7 summarises the results presented in these five empirical chapters, and places our findings in the context of the existing literature. We discuss the limitations of the research, and offer some suggestions for future study.

付記する学位プログラム名: 霊長類学・ワイルドライフサイエンス・リーディング大学院 / 京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22295号 / 理博第4609号 / 新制||理||1661(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 古市 剛史, 教授 湯本 貴和, 教授 濱田 穣 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

In social primates, the acquisition and maintenance of social dominance may augment reproductive success while incurring immunological costs. This trade-off is hypothetically facilitated by hormones that modulate both status-enhancing behavior and immune function. In the three studies comprising this dissertation, I investigated hormonal mechanisms by which social dominance may reflect immune health, testing relationships between behavioral correlates of dominance rank, steroid hormone secretion, and immune activity in wild adult male chimpanzees (Pan troglodytes schweinfurthii). Between January 2016 and July 2017, I collected behavioral observations and urine samples from adult males at Ngogo in Kibale National Park, Uganda, home to the largest community of habituated wild chimpanzees yet described. In the first study, I assessed behavioral and anatomical mechanisms that may link dominance rank to the secretion of testosterone, the primary male sex hormone. Testosterone was positively correlated with dominance rank and creatinine, a product of muscle catabolism and noninvasive proxy for lean muscle mass. Contrary to expectations, testosterone was negatively correlated with overall rates of aggression, indicating that aggressiveness does not itself account for positive linear correlations between dominance and testosterone in this species. In the second study, I analyzed reproductively salient correlates of cortisol, a glucocorticoid hormone secreted in response to psychosocial and metabolic demands. Urinary measures of reproductive effort and immune challenge were positively correlated with cortisol, indicating adaptive energy allocation. Furthermore, dominance rank was positively correlated with urinary cortisol when c-peptide of insulin, as a measure of energy intake, was low. This indicates that high ranking males deprioritize energy intake in certain social contexts, including competition for sexually receptive mates. In the third study, I found that although urinary testosterone seemingly diminished immune function, high ranking males were less likely to die from severe acute immune challenge than low ranking conspecifics. My results provide evidence that mating effort increases immune challenge both by increasing testosterone secretion and reallocating energy away from immune function. However, despite the increased mating effort exhibited by high ranking males, social dominance does not incur notable immunological costs. On the contrary, social dominance likely reflects immunocompetence and male quality in nonhuman primates. / 2021-12-06T00:00:00Z

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付記する学位プログラム名: 霊長類学・ワイルドライフサイエンス・リーディング大学院 / 京都大学 / 新制・課程博士 / 博士(理学) / 甲第23747号 / 理博第4837号 / 新制||理||1692(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 平田 聡, 教授 伊谷 原一, 教授 村山 美穂 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

<p>To assess how the plasticity of the face processing system changes with age, we trained 8-year-olds, 10-year-olds, and adults to differentiate 10 chimpanzee faces at the individual level for 3 days by having them watch a child-friendly training video. Their improvement from baseline was compared to that of age- and gender-matched controls who completed the pre- and post-tests, but did not complete training. Improvement did not vary across age: 8-year-olds, 10-year-olds, and adults all showed similar improvement in accuracy at discriminating the 10 chimpanzee faces on which they were trained. This improvement resulted in the reduction of the own-species bias after training. However, the benefits of training did not generalize to novel exemplars. In addition, participants from both the training and control groups showed a practice effect: their accuracy at discriminating both chimpanzee and human faces improved from pre- to post-test. Taken together, these results demonstrate that the face processing system is somewhat plastic between 8 years of age and adulthood and suggest that this plasticity remains stable throughout this period of development.</p> / Master of Science (MSc)

Intestinal flora of wild chimpanzee has not been studied. Fecal flora analyses currently give insight to this environment. We collected feces from twelve human-habituated wild chimpanzees in each of three age groups: four juveniles, four sub-adults, and four adults. We analyzed fecal samples using Terminal-Restriction Fragment Length Polymorphism (T-RFLP) of amplified 16S rRNA genes to determine bacterial diversity present. Between 1 and 14 terminal-restriction fragments (T-RFs) were observed in each sample. A total of 26 unique T-RFs were produced from the samples and ranged in size from 92 to 837 base pairs (bps). Twenty-four of these T-RFs corresponded to five bacterial phyla: Actinobacteria, Bacteroidetes, Firmicutes, Mollicutes, and Proteobacteria, as well as uncultured and unidentified bacterial species. The remaining T-RFs corresponded solely to uncultured or unidentified bacteria. Firmicutes was the most common phylum, observed in 11 of the samples. Bacteroidetes was the second-most common phylum, detected in 8 of the samples. Principal Components Analysis (PCA) revealed a discrete clustering of 10 samples when looking at components one and two, and a clustering of 11 samples when looking at component three. These three components accounted for 72.5% of the variation within the data. Morisita indices were computed to compare T-RF profiles of two samples at a time, and were between 0 and 0.886. Results indicated that some fecal bacterial profiles were similar in the study group, but ultimately varied between samples when compared two at a time. Specific diet, physiology, and environmental reservoir exposure may play large roles in shaping such profiles. / Master of Science

<p>In chimpanzees, most females disperse from the community in which they were born to reproduce in a new community, thereby eliminating the risk of inbreeding with close kin. However, across sites, some females breed in their natal community, raising questions about the flexibility of dispersal, the costs and benefits of different strategies and the mitigation of costs associated with dispersal and integration. In this dissertation I address these questions by combining long-term behavioral data and recent field observations on maturing and young adult females in Gombe National Park with an experimental manipulation of relationship formation in captive apes in the Congo.</p><p>To assess the risk of inbreeding for females who do and do not disperse, 129 chimpanzees were genotyped and relatedness between each dyad was calculated. Natal females were more closely related to adult community males than were immigrant females. By examining the parentage of 58 surviving offspring, I found that natal females were not more related to the sires of their offspring than were immigrant females, despite three instances of close inbreeding. The sires of all offspring were less related to the mothers than non-sires regardless of the mother’s residence status. These results suggest that chimpanzees are capable of detecting relatedness and that, even when remaining natal, females can largely avoid, though not eliminate, inbreeding.</p><p>Next, I examined whether dispersal was associated with energetic, social, physiological and/or reproductive costs by comparing immigrant (n=10) and natal (n=9) females of similar age using 2358 hours of observational data. Natal and immigrant females did not differ in any energetic metric. Immigrant females received aggression from resident females more frequently than natal females. Immigrants spent less time in social grooming and more time self-grooming than natal females. Immigrant females primarily associated with resident males, had more social partners and lacked close social allies. There was no difference in levels of fecal glucocorticoid metabolites in immigrant and natal females. Immigrant females gave birth 2.5 years later than natal females, though the survival of their first offspring did not differ. These results indicate that immigrant females in Gombe National Park do not face energetic deficits upon transfer, but they do enter a hostile social environment and have a delayed first birth. </p><p>Next, I examined whether chimpanzees use condition- and phenotype-dependent cues in making dispersal decisions. I examined the effect of social and environmental conditions present at the time females of known age matured (n=25) on the females’ dispersal decisions. Females were more likely to disperse if they had more male maternal relatives and thus, a high risk of inbreeding. Females with a high ranking mother and multiple maternal female kin tended to disperse less frequently, suggesting that a strong female kin network provides benefits to the maturing daughter. Females were also somewhat less likely to disperse when fewer unrelated males were present in the group. Habitat quality and intrasexual competition did not affect dispersal decisions. Using a larger sample of 62 females observed as adults in Gombe, I also detected an effect of phenotypic differences in personality on the female’s dispersal decisions; extraverted, agreeable and open females were less likely to disperse. </p><p>Natural observations show that apes use grooming and play as social currency, but no experimental manipulations have been carried out to measure the effects of these behaviors on relationship formation, an essential component of integration. Thirty chimpanzees and 25 bonobos were given a choice between an unfamiliar human who had recently groomed or played with them over one who did not. Both species showed a preference for the human that had interacted with them, though the effect was driven by males. These results support the idea that grooming and play act as social currency in great apes that can rapidly shape social relationships between unfamiliar individuals. Further investigation is needed to elucidate the use of social currency in female apes.</p><p>I conclude that dispersal in female chimpanzees is flexible and the balance of costs and benefits varies for each individual. Females likely take into account social cues present at maturity and their own phenotype in choosing a settlement path and are especially sensitive to the presence of maternal male kin. The primary cost associated with philopatry is inbreeding risk and the primary cost associated with dispersal is delay in the age at first birth, presumably resulting from intense social competition. Finally, apes may strategically make use of affiliative behavior in pursuing particular relationships, something that should be useful in the integration process.</p> / Dissertation