Browsing by Department "Evolutionary Anthropology"
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Item Open Access A 3D Geometric Morphometric Investigation of Relatedness in the Modern Human, Chimpanzee, and Homo naledi Postcranial Skeleton(2023) Rossillo, Amanda NoelleStudies of skeletal variation form the basis of our understanding of our species’ history and diversity. This most commonly takes the form of comparative, between- species studies aimed at reconstructing phylogenetic relationships. However, studies of within-species variation can provide insights into relatedness at smaller scales, which can shed light on important microevolutionary processes and be used to identify closely related individuals in the absence of DNA. This dissertation assesses the relationship between genetic and skeletal variation within groups of related and unrelated Homo sapiens and Pan troglodytes, with the aim of better understanding the population sampled by the seemingly homogenous Homo naledi assemblage from the Dinaledi Chamber in Rising Star Cave, South Africa. The hypotheses tested were: 1) closely related individuals exhibit less skeletal variation compared to unrelated individuals, and 2) the Dinaledi assemblage exhibits less morphological variation than H. sapiens and P. troglodytes at the species level, more closely resembling a single population.
Skeletal variation within a subset of H. sapiens from the crypt of Christ Church in Spitalfields, London (17-19th centuries A.D) with documented genealogies and the Gombe population of P. t. schweinfurthii was compared to species-wide baselines and the H. naledi assemblage. The data consisted of 3D models of 556 postcranial elements (first metacarpal (Mc1), proximal femur, talus, calcaneus, and navicular) from 187 individuals that were generated from surface scanners or downloaded from MorphoSource.
This dissertation employed a relatively new 3D geometric morphometric workflow that captures the entire shape of an element through the use of an automated landmarking program and feature-aware registration process. Two hundred pseudolandmarks were automatically and optimally placed on each element. Following alignment, multiple univariate and multivariate statistical analyses were used to quantify shape variation within and between the three species, including distributions of Euclidean distances, Procrustes distances to the mean shapes, Principal Components Analyses (PCA), Between-Group PCA, and Discriminant Function Analyses. The coefficient of relationship was used to represent genetic distance between known genetic relatives within modern humans.
The results of the within-species analyses of skeletal variation support Hypothesis 1 in both modern humans and chimpanzees, though the signal of relatedness is differentially expressed within and across elements. In modern humans, the calcaneus can be used to distinguish known close relatives from distantly related and unrelated individuals. The navicular and femur were also found to be relatively good indicators of relatedness. Within chimpanzees, the talus is the most effective at distinguishing the Gombe population from the species-wide chimpanzee sample, followed by the calcaneus and femur. Within H. naledi, the talus varied the least while the navicular varied the most, though the high levels of variation found in the navicular and Mc1 are likely due to the state of preservation of these elements. The results of the interspecies analyses are more ambiguous. When considering the best preserved elements, the H. naledi talus varies the least within the three species, while the femur varies more than those of either H. sapiens or P. troglodytes at the species level. Hypothesis 2 is thus supported for the talus while rejected in the femur, suggesting that it cannot be rejected as a whole and that the patterns of homogeneity previously observed within H. naledi are more nuanced than previously recognized.
Item Open Access A Mechanical Analysis of Suspensory Locomotion in Primates and Other Mammals(2016) Granatosky, Michael ConstantineFor primates, and other arboreal mammals, adopting suspensory locomotion represents one of the strategies an animal can use to prevent toppling off a thin support during arboreal movement and foraging. While numerous studies have reported the incidence of suspensory locomotion in a broad phylogenetic sample of mammals, little research has explored what mechanical transitions must occur in order for an animal to successfully adopt suspensory locomotion. Additionally, many primate species are capable of adopting a highly specialized form of suspensory locomotion referred to as arm-swinging, but few scenarios have been posited to explain how arm-swinging initially evolved. This study takes a comparative experimental approach to explore the mechanics of below branch quadrupedal locomotion in primates and other mammals to determine whether above and below branch quadrupedal locomotion represent neuromuscular mirrors of each other, and whether the patterns below branch quadrupedal locomotion are similar across taxa. Also, this study explores whether the nature of the flexible coupling between the forelimb and hindlimb observed in primates is a uniquely primate feature, and investigates the possibility that this mechanism could be responsible for the evolution of arm-swinging.
To address these research goals, kinetic, kinematic, and spatiotemporal gait variables were collected from five species of primate (Cebus capucinus, Daubentonia madagascariensis, Lemur catta, Propithecus coquereli, and Varecia variegata) walking quadrupedally above and below branches. Data from these primate species were compared to data collected from three species of non-primate mammals (Choloepus didactylus, Pteropus vampyrus, and Desmodus rotundus) and to three species of arm-swinging primate (Hylobates moloch, Ateles fusciceps, and Pygathrix nemaeus) to determine how varying forms of suspensory locomotion relate to each other and across taxa.
From the data collected in this study it is evident the specialized gait characteristics present during above branch quadrupedal locomotion in primates are not observed when walking below branches. Instead, gait mechanics closely replicate the characteristic walking patterns of non-primate mammals, with the exception that primates demonstrate an altered limb loading pattern during below branch quadrupedal locomotion, in which the forelimb becomes the primary propulsive and weight-bearing limb; a pattern similar to what is observed during arm-swinging. It is likely that below branch quadrupedal locomotion represents a “mechanical release” from the challenges of moving on top of thin arboreal supports. Additionally, it is possible, that arm-swinging could have evolved from an anatomically-generalized arboreal primate that began to forage and locomote below branches. During these suspensory bouts, weight would have been shifted away from the hindlimbs towards forelimbs, and as the frequency of these boats increased the reliance of the forelimb as the sole form of weight support would have also increased. This form of functional decoupling may have released the hindlimbs from their weight-bearing role during suspensory locomotion, and eventually arm-swinging would have replaced below branch quadrupedal locomotion as the primary mode of suspensory locomotion observed in some primate species. This study provides the first experimental evidence supporting the hypothetical link between below branch quadrupedal locomotion and arm-swinging in primates.
Item Open Access Adaptive Motivations Drive Concern for Common Good Resources(2019) Bowie, Aleah CHumans universally demonstrate intrinsically motivated prosocial behavior towards kin, non-kin ingroup members, and strangers. However, humans struggle to extend the same prosocial behavior to more abstract concepts like future-others and non-human species. The Adaptive Motivation Hypothesis posits that humans evolved intrinsic motivations to act prosocially towards more tangible social partners like those within an individual’s ingroup, but prosocial behavior towards more distant and abstract partners is constrained by ecological certainty. Prosocial behavior towards these more abstract concepts is more variable and more likely motivated by extrinsic reward. This dissertation aims to examine the development of motivations for prosocial behavior towards these more abstract concepts. My studies rely on common goods games as a proxy for examining behavior towards abstract recipients of prosocial behavior. Common goods are any resource like forests or fisheries that are non-excludable to a population, but rivalrous. In-demand common goods require cooperation of humans to ensure sustainable use in order to avoid depletion. Chapter One examined how children in three populations that differed in ecological certainty behaved in a common goods game where they were asked to contribute portions of their personal endowment to the maintenance of a forest. Participants were either provided a high extrinsic motivation, a low extrinsic motivation, or no extrinsic motivation for contributing to the maintenance of the common good. Results show that overall, children of all ages were more motivated to contribute to abstract recipients when extrinsic motivation is high. However, noticeable variation in behavior between populations was driven by ecological and cultural differences. Chapter Two examined whether aggregated extrinsic rewards increased contributions to common goods in a sample of children aged six to fourteen. Results suggest that both information about personal loss and delay in an acquiring resource together dramatically increase children’s contributions to common goods within both experimental and real-world contexts. Chapter Three explores whether making a typically abstract social partner more tangible increases an individual’s prosocial behavior towards said partner. Results for Chapter Three, conducted with a population in the Democratic Republic of the Congo, find that increasingly the tangibility of an abstract population marginally increases prosocial behavior in children but not in adults. Together, the results of these studies have implications improved understanding of the development of prosocial motivations in school age children, as well as applications to understanding motivations for socially conscious behavior in the face of environmental and conservation dilemmas.
Item Open Access Biomechanics of Vertical Clinging and Grasping in Primates(2012) Johnson, LauraPrimates and many other animals that move in an arboreal environment often cling, sometimes for long periods, on vertical supports. Primates, however, face a special challenge in that almost all primates bear nails on the tips of their digits rather than claws. Squirrels and other arboreal animals possess claws and/or adhesive pads on their digits in order to hold their weight on vertical substrates. Assuming the ancestral primate was arboreal and lost claws prior to the radiation of primates this paradox has important implications and raises a significant question about living primates and early primate evolution: how can primates maintain vertical postures without claws and how did early primates meet this challenge? Primate vertically clinging and grasping postures (VCG) have been studied in the wild and theoretical models of VCG postures have been described. This dissertation builds on this work, by studying the biomechanics of VCG postures in primates. Based on mechanical models, it was hypothesized VCG posture in primates will vary in three ways.
Hypothesis 1: Species with different morphological features associated with different locomotor modes will vertically cling and grasp in different ways.
Hypothesis 2: As substrate size increases, primates will place their arms to the side of the support and adjust posture and muscle recruitment in order to maintain a necessary tangential to normal force ratio to resist gravity.
Hypothesis 3: On substrates of the same relative size, larger animals should be less effective at maintaining VCG postures due to scaling relationships between muscle strength and body mass.
The sample consisted of multiple individuals from eight strepsirrhine species at the Duke Lemur Center. The sample varied in locomotor mode--habitual vertical clinging and leaping (VCL) compared to less specialized arboreal quadrupeds--and body mass--100 to 4,000 grams. Subjects were videorecorded while holding VCG postures on substrates of increasing size. Substrate preference data were calculated based on frequency and duration of VCG postures on each substrate. Qualitative kinematic data were recorded for a maximum of thirty trials per individual, per substrate. Angular data were calculated for forelimbs and hindlimbs from these videos for ten trials per individual per substrate. In addition, kinetic data from an imbedded force transducer were collected for two species that vary in locomotor mode, but not body mass.
There are several significant and relevant results from this study that address both primate functional anatomy and locomotor evolution. Hypothesis one was supported by hand and hindlimb joint postures, shown to be highly sensitive to locomotor mode. VCL primates exhibited deeply flexed limbs and more hand grasping (wrapping around the substrate) versus parallel hand postures and use of bowed finger postures compared to less specialized primates. Kinetically, species were shown to bear the majority of their weight in their hindlimbs relative to their forelimbs. The forelimb joints and foot showed little variation by habitual locomotor mode. Hypothesis two found support in that species tend to prefer smaller substrates, clinging less frequently for shorter durations as substrate size increases. Hand posture changed as size increased, as primates (except for the slow lorises) in this study grasped with their pollex on smaller substrates, but the pollex disengaged in grasping on larger substrates. Hypothesis three was not supported; body mass did not influence VCG postures.
Taken together, the finding that the forelimb held a wide range of postures on each substrate size for all species and played a limited role in weight-bearing suggests the forelimb free to move (to adjust posture and or forage). The hindlimb plays a more specific role in weight-bearing and is more sensitive to variations in primate anatomy. Additionally, these findings lead to hypotheses concerning the relatively short pollexes of primates, and that the ancestral primate was smaller than 100g and preferred small substrates as found in a fine-branch niche.
Item Open Access Bite Into This: Preliminary Analysis of Jaw-Adductor Muscle Architecture and Bite Force Measured from DiceCT Images in Tupaia and Strepsirrhine Primates(2017-05-10) Jain, KavitaFeeding is a complex behavior involving the synchronization of the mandible, maxilla, muscles of mastication and temporomandibular joint. I quantify the anatomy and three-dimensional architecture of the jaw adductor muscles in a sample of strepsirrhine primates in order to examine how bite force vectors relate to body size, jaw morphometrics, and diet. I hypothesized that species feeding on tough, stiff foods will generate high vertical bite forces on the Phase I Shearing Plane. Additionally, I evaluated (1) the relationship between the vertical component of bite forces to body mass, (2) if muscle fibers were arranged to provide the largest mechanical advantaged in producing a vertical component of bite force, and (3) how tooth wear affects performance estimates. I found that vertical bite forces were higher on the Phase I Crushing Plane. Furthermore, there was a link between body mass and vertical bite force; muscle fibers may be angled to provide a mechanical advantage depending on diet; and tooth wear did seem to influence the occlusal planes, thus affecting performance estimates. The data here provide important in situ estimates for the vertical component of bite force, muscle force, and the vertical component of joint forces which can be compared to and combined with similar studies to determine the best method of muscle analysis and force estimates. Understanding how the jaw adductor system functions we can evaluate and estimate how this system and the environment around it (through diet) has influenced the evolution of the skull.Item Open Access Body Mass Prediction from Dental and Postcranial Measurements in Primates and Their Nearest Relatives(2017) Yapuncich, Gabriel StephenTo evaluate alternative hypotheses for the role of mass and muscle-induced forces in joint construction, the allometric scaling relationships of the articular facets of the talus were estimated with phylogenetic regressions. Many articular surfaces scale with significant positive allometry, suggesting that mass-induced forces are an important influence for the bony architecture of synovial joints.
Using a large sample of primates and their nearest living relatives, body mass prediction equations were generated from the articular facet areas of the talus and calcaneus. Those facets that scaled with positive allometry were both accurate and precise. Compared to previously published prediction equations, the novel equations developed for this study were substantially more reliable.
Several methodological debates for body mass prediction were also evaluated. Prediction equations had their highest correlations when species with greater than a 20% difference between sexes are represented by both males and females. Using dental measurements from cercopithecoids housed at the National Museum of Natural History, predictive accuracy was maximized when body mass was predicted using a mean value estimated from a robust sample. Even when only a single individual was represented, tests of predictive accuracy using primates with associated body masses from several localities (Hacienda La Pacifica, Costa Rica; Gombe Stream National Park, Tanzania; Amboseli Reserve, Kenya; and the Duke Lemur Center) demonstrated that prediction equations provide more accurate predictions of species mean values than individual-specific values.
The importance of longitudinal change in body mass was evaluated by comparing coefficients of variation for individual and mean body mass of the populations at La Pacifica, Gombe, and the Duke Lemur Center. Individual coefficients of variation were significantly greater than the population coefficients of variation, which suggests that mean body masses are more stable “targets” of prediction.
Finally, the novel prediction equations were applied to a sample of sympatric primates with associated dental and postcranial elements from the middle Eocene of Wyoming, including Notharctus tenebrosus, Smilodectes gracilis, Omomys carteri, and Hemiacodon gracilis. New body mass predictions suggest two pairs of similarly sized primates: N. tenebrosus and S. gracilis (~2500g), and O. carteri and H. gracilis (~400g). Thus, niche partitioning between closely related taxa was probably achieved through differences in diets, rather than differences in body mass.
Item Open Access Characterizing sleep-wake cycles in dogs (Canis lupus familiaris) using daytime activity levels, sex, and temperament: a longitudinal comparison(2024-04-12) Sandberg, EmilyAcross many species, sleep patterns are associated with variables such as age, sex, daytime activity levels, and temperament. Yet, current research lacks an in-depth characterization of dog sleep patterns and how they vary according to these variables during the critical developmental period of young puppyhood. Such studies are crucial in order to establish dogs as a model organism for studies of sleep and for additional applications in the realms of dog welfare and training. In the present study, we characterized how often and for how long young dogs wake, as well as their barking patterns during sleep. We evaluated sleep behaviors for dogs aged 8-18 weeks and determined longitudinal patterns using a sample of Canine Companions service-dogs-in-training (N=21). Video recordings of dogs were analyzed using a novel coding scheme to determine duration and frequency of awake bouts and barking. Mixed-effects logistic regression models reveal that awake-bout length (minutes) and frequency did not vary significantly by weeks of age, daytime activity levels, or temperament. However, we did find significant sex differences in awake bout length (p<0.009). These results suggest distinct daytime and nighttime temperaments, as well as the importance of this developmental period for developing adultlike sleep patterns. Further study is required to examine sleep behaviors in puppies beyond 18-weeks to better understand how adultlike patterns emerge and the stability of the patterns observed in this study.Item Open Access Dental Ecometrics as a Proxy of Paleoenvironment Reconstruction in the Miocene of South America(2017) Spradley, Jackson PlesIn this dissertation I compile modern mammalian faunal lists, as well as ecomorphological measurements on living marsupials and rodents, to relate the diversity of small mammals, specifically the distributions of their dental topographies, to the climates in which they are found. The emphasis of this dissertation is to demonstrate the potential of distributions of dental topography metrics as proxies for the reconstruction of paleoenvironments in the Miocene of South America.
In Chapter 2, I compile complete, non-volant mammalian species lists for 85 localities across South America as well as 17 localities across Australia and New Guinea. Climatic and habitat variables were also recorded at each locality using GIS spatial data. Additionally, basic ecological data was collected for each species, including: diet, body size, and mode of locomotion. Niche indices that describe the relative numbers of different ecologies were calculated for each locality. These indices then served as the predictor values in a handful of regression models, including regression trees, random forests, and Gaussian process regression. The Australian/New Guinean localities were used as a geographically and phylogenetically independent for the purposes of testing the models derived from South America.
As for the dental ecomorphological analysis, I use three separate measures of dental topography, each of which measures a different component of dental topography; relief (the Relief Index, or RFI), complexity (orientation patch count rotated, OPCR), and sharpness (Dirichlet normal energy, DNE). Together, these metrics quantify the shape of the tooth surface without regard for tooth size. They also do not depend on homologous features on the tooth surface for comparative analysis, allowing a broad taxonomic sample as I present here. After a methodological study of DNE in Chapter 3, I present correlative studies of dental topography and dietary ecology in marsupials and rodents in Chapters 4 and 5, respectively. Finally, using the same localities from Chapter 2, I analyze the distributions of dental topography metrics as they relate to climate and habitat.
Results suggest that sharpness and relief are positively correlated with a higher amount of tough foods—such as leaves or insects—in the diet of marsupials, and that relief is positively correlated with grass-eating in rodents. The distributions of all three metrics show some utility when used as a proxy for climatic variables, though the distributions of RFI in marsupials and OPCR in rodents demonstrate the best correlations.
Overall, this dissertation suggests that dental topography can be used to discriminate dietary categories in a wide variety of mammalian groups, and that the distributions of dental ecometrics can be used as proxies for paleoenvironment reconstruction. This may eliminate the need to reconstruct behavior in individual taxa in order to construct ecological indices for fossil mammalian communities, thus offering a more direct avenue to reconstructing past environments.
Item Open Access Descending Locomotion in Primates(2019) Perchalski, Bernadette AlycePrimates are an order of mammals that lack claws. Therefore, arboreal primates must apply opposing pressures with their digits to grasp supports and move through their habitats. This requirement may affect the mechanics of specific aspects of arboreal travel, such as descent, in the locomotion of primates compared to clawed non-primates, and may have influenced the evolutionary selective pressures that primates experienced over time. It has been hypothesized that larger primates are less likely to descend supports headfirst than smaller primates and clawed non-primates, however, this phenomenon has never been considered in a comparative context. Knowing how body size, anatomical proportions, and environment interact to affect locomotor behaviors is central to linking morphology with behavior, such as when evaluating hypotheses of primate origins.
This thesis analyzed descending locomotion in nine species of strepsirrhine primates that occupy four locomotor categories: large arboreal generalists, representing above branch quadrupeds weighting over 1 kg; small arboreal generalists, representing above branch quadrupeds under 1 kg; slow climbers; and vertical clingers and leapers. Primates were video recorded moving on supports ranging from horizontal to vertical in 15° increments. I tested specific hypotheses about gait and kinematic changes in response to declines that have been observed in primates moving down supports as steep as approximately 30° to see if these patterns would be replicated in primates moving on steeper support orientations.
I found that primates under 1 kg always used headfirst descent on all supports. For primates above 1 kg, body size appeared to be an important factor in determining behavior, but it also appeared that anatomical differences might have enabled one of the largest species in the sample, Varecia variegata, to perform vertical headfirst descent, while relatively smaller species like Lemur catta were not observed to use this behavior on supports greater than 45°. Within these large arboreal generalists, increases to individual age also seemed to drive behaviors away from headfirst descent in favor of tail first descent. Frequencies of headfirst descent were compared to other mechanisms of descent, such as tail first descent, were scored for a total of 3139 observed descents. These observations were incorporated into a Bayesian multilevel model that included information on the support condition (including orientation and diameter), morphological information for each species (average intermembral index and foot proportions), as well as individual mass and age. The model was then used to predict the probability of headfirst descent on various supports in simulated ancestral primates that exemplified different hypotheses of primate origins. It was found that features including body mass, support orientation, and foot and limb proportions greatly affected the predicted probabilities of headfirst descent. Large primates with lower intermembral indices and smaller feet were least likely to use headfirst, especially as supports became more steeply angled. Species that were smaller, with relatively longer arms or larger feet tend to use headfirst descent most frequently, even on vertical supports. The model predicted less headfirst descent in the very smallest primates on near horizontal supports, driven by observations of leaping in the smallest species in this sample.
Headfirst descents were analyzed for footfall patterns to evaluate temporal aspects of gait, and to test the hypothesis that limb phase should decrease as supports become steeper and that contact period with the support should increase, and relatively more so for the forelimbs than hind limbs. It was found that limb phase did significantly decrease across the sample as support orientation became steeper, and that both forelimb and hind limb contact times increased as proportion of the total stride period, although the forelimb did not increase relatively more than the hind limb in many species.
Headfirst descents were then analyzed for changes to kinematic aspects of gait including effective limb length, joint angles at key points during the stride, limb excursions, and velocity. I found that as supports became steeper primates across the sample reduced trunk inclination bringing the body parallel to the support and reducing the distance of the center of mass from the support, consistent with pitch-avoidance strategies. The forelimb remained compliant and highly protracted with increasing support orientation; the hind limb did not remain complaint and instead became significantly retracted in primates travelling on supports of 60° and steeper. Speed was generally reduced as support orientation increased.
Overall this study demonstrated that strepsirrhine primates capable of headfirst descent span a range of body masses up to approximately 4 kg in this sample. Across this range of body masses common strategies for traveling headfirst on supports included adopting slow trotting gaits with extended periods of hind limb retraction and forelimb protraction. Species that did not perform headfirst descent may have been limited in their ability to perform this behavior by aspects of their anatomy, such as having relatively short arms or less developed muscles for pedal grasping compared to species that were more adept at headfirst descent.
Placing these results into an evolutionary context, a small primate ancestor would be least impacted in its ability to navigate using headfirst descent on supports of all angles, whereas a larger ancestral primate might have been limited in the arboreal supports it could have navigated headfirst. Leaping may have been an alternative to grasping mediated headfirst descent in very small early primates, while alternatives to headfirst descent, such as tail first decent, that were only observed in larger species might have emerged later as various primate lineages increased in body mass but retained the characters of primate origins, grasping feet and nails.
Item Open Access Differential habitat use as a behavioral thermoregulatory strategy in lemurs(2014-05-09) Arcia Ramos, JaniaIn order to reduce the energetic cost of controlling internal body temperatures physiologically, animals engage in “behavioral thermoregulatory activities.” These strategies include changing postures, social huddling, and moving to different levels of the forest canopy in response to environmental changes. For lemurs, behavioral thermoregulation can be especially important to be able to cope with the daily and seasonal climatic variations of their habitat because they have a lower basal metabolic rate than other primates. In this study, we analyzed the patterns of temperature and humidity variation throughout the forest at the Duke Lemur Center and then analyzed how individuals of Propithecus coquereli and Lemur catta use these variations as a strategy for behavioral thermoregulation. We found that generally temperatures tended to decrease deeper into the forest, with a few deviations from this pattern during fall, and for different forest coverage. We also found that humidity generally increased deeper into the forest, although this pattern reversed for the deciduous enclosures during the fall months. When analyzing how the lemurs use the forest in response to temperature variation, we found that contrary to what we expected, individuals preferred to spend the majority of their time at “edge” or “out” of the forest for all temperatures, and spent very little time at the interior of the forest (30m or 60m). This was also the case when we controlled for sun exposure levels. However, individuals did employ other behavioral thermoregulatory strategies, including increasing extended postures during hotter temperatures and increasing tucked postures during cooler ones, yet there was no clear relationship between the employment of this strategy and the use of forest depth. Possible explanations for the data were explored, including the effect of human interaction. In order to establish more concise patterns for the use of microhabitat selection as a form of behavioral thermoregulation, further research should increase the range of temperatures and the length of the study.Item Open Access Dispersal and Integration in Female Chimpanzees(2015) Walker, Kara KristinaIn 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.
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.
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.
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.
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.
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.
Item Open Access Do females have friends? The nature of social bonds among female chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania(2014-05-08) McLellan, KarenChimpanzee (Pan troglodytes schweinfurthii) females have traditionally been viewed as asocial and solitary, but recent evidence suggests that they are more social than previously believed and may develop differentiated social bonds like their more gregarious male counterparts. Here we use 38 years of long-term behavioral and spatial data from Gombe National Park, Tanzania to test whether chimpanzee females have differentiated social bonds and whether these bonds are primarily explained by spatial or social factors. We found that female association and grooming relationships were well differentiated. Kin dyads associated, ranged, and groomed preferentially, regardless of rank. Non-kin dyads associated at consistently lower rates than kin dyads, with rank difference likely playing a mediating role between spatial overlap and association preferences. These results demonstrate that strong social bonds do exist among female chimpanzees, but that these bonds are primarily among kin dyads.Item Open Access Do sex differences affect behavioral thermoregulatory strategies in lemur species?(2013) Hukins, Mariah S.Thermoregulation is the ability for an animal to maintain its internal body temperature. Due to the high costs of regulating temperature physiologically, behavioral thermoregulation is more energy efficient. While previous studies have characterized thermoregulatory behaviors in mammals, few have examined how sex differences influence thermoregulatory behaviors. Sex differences in energy costs can be attributed to the contrast in male and female parental investment. Females endure more energetic costs while pregnant as well as costs of lactation. Males on the other hand acquire smaller energetic costs for sperm production and male-male competition during the breeding season. Lemurs make for interesting models to test for sex differences in behavioral thermoregulation as they have relatively low metabolic rates and clear sex differences in parental investment. Here we test the hypothesis that females will exhibit greater use of thermoregulatory behaviors than males using 21 individuals from 3 species of lemurs (Lemur catta, Eulemur flavifrons, Eulemur mongoz) housed at the Duke Lemur Center. Data collection involved scan samples recording behavior, sun or shade exposure, substrate, individual identification, ambient temperature, wind and humidity. Data analysis indicates no clear sex difference in behavioral thermoregulation. Males and females both showed use of thermoregulatory behaviors through decreasing energy conserving behaviors as temperature increased. In some instances, females also displayed patterns opposite of what was expected. Data was further distinguished between breeders and non-breeders but no clear patterns were found. Overall, these results suggest no clear sex difference of behavioral thermoregulation.Item Open Access Does our perception of animals shape when we see all humans as being created equally?(2022) Zhou, WenHumans are paradoxical in their ability for extreme kindness and cruelty. The goal of this dissertation is to further uncover the psychological mechanism(s) that allow humans to accept harm directed at members of other groups. The human self-domestication hypothesis proposes that human unique forms of mentalizing evolved as a byproduct of selection for ingroup prosociality. Hare (2017) proposed that late in human evolution Homo sapiens bonded more closely with ingroup members and more skillfully read the mental states of others. Moral and cultural behaviors expanded, and modern human behavior emerged. However, more closely bonded groups tend to perceive outgroup strangers as more threatening. It became advantageous to deny some forms of human-unique mental states to individuals from threatening groups. In this way emotional and moral constraints on violence toward other humans can be escaped. The potential for lethal aggression and harm toward outgroup strangers became even more extreme as a result. According to this model there should be strong psychological links between group identity, mental state attribution, moral exclusion, and a willingness to harm others. Two main mechanisms have been proposed to provide this link. The first is dehumanization or the ability to deny fully human emotions and mental abilities to another person or group of people (Haslam, 2006). The second is social dominance orientation or the perception of a hierarchy between different human groups (Sidanius & Pratto, 2001). Together these mechanisms can override individual characteristics that lead to concern. Group identity alone can be used to indicate inferiority or less than human status. Moral exclusion and harm can follow. More recently a third moderating factor has been proposed. Costello & Hodson (2010) proposed that beliefs about animals strongly shape tendencies to dehumanize. Seeing animals as having human-like minds negates the negative impact of dehumanization since being nonhuman is so similar to being human. In Chapter 1, I combine this evolutionary model with the proposed mechanisms that drive the worst forms of group-based aggression to propose the Dehumanization of Inferior Groups (DIG) Hypothesis. The DIG hypothesis suggests the perception of other groups of humans is strongly modulated by how we view the minds of other animals, their relationship with each other and our relationship to them. Our minds evolved to distinguish between humans and animals, but we develop the ability to categorize some members of our own species as more animal-like. We also evolved to categorize the relative equality or inequality of different groups. This includes groups of animals that can be perceived as different but equal or ranked hierarchically. How we perceive different groups of animals will relate to how hierarchically we view different groups within our own species. The present dissertation seeks to provide initial tests of the DIG hypothesis. To do so, I used experiment-based surveys, investigating behavioral patterns of adults and school age children. In Chapter 2, I assessed dehumanizing tendency in adults and children, revealing that variety of humanness representations can elicit dehumanization in both age groups. Similar to the links seen in previous investigations of adults, children’s willingness to dehumanize is related to their acceptance that other groups can be inferior and more deserving of punishment. In Chapter 3, I examined the association between the perception of animal-to-human similarity and dehumanization. Results in adults and children showed that highlighting mental similarities between animals and humans could narrow down the perceived animal-human divide. However, in both age group, this manipulation does not attenuate dehumanization or the intergroup biases associated with it. Chapter 4 explored the association between the treatment of other human groups and the treatment of animals in a variety of participants who were engaged in different relationship with animals. I found that people who endorsed discrimination of dog breeds also endorsed group-based discrimination in human society. Moreover, positive contact with dogs is associated with disapproval of group-based inequality. Together, these findings suggest that the perception of human intergroup relations and the perception of relationship among animal groups are dependent upon similar cognitive processes. The studies presented here have implications for understanding psychological origins of dehumanization as well as designing interventions to promote intergroup tolerance.
Item Open Access Does posture at death reveal behavior patterns?(2018-04-24) Galvez, Ana IxchelStudies on functional morphology are common in the field of evolutionary anthropology. Many anthropologists observe and meticulously record the locomotor behavior of primates, categorize them, and seek to understand how their anatomical features either aid or constrain them in their movements. Correlations can be made between robust, funny-shaped, or non-existent skeletal features and the range of movement (ROM) capabilities of the animal. Using traditional methods of measuring cadaveric specimens in order to discern species-specific morphological features has been done for a long time, but no one has thought to look at cadaveric posture as a method of inferring behavior in strepsirrhine primates. This study utilized 3D digital models of articulated hands to measure hand angles as a proxy for hand posture, with the goal of determining if death posture covaries with bony morphology and locomotor behavior. We found that the hand angle measurement protocol developed for this study can reliably measure ROM and that there is statistically significant evidence of unequal variance between species attributed to species-specific differences in posture. Principle Components Analysis (PCA) conducted on carpal morphology indices yielded some strong, grouped correlations, suggesting that there are interspecific variances attributed to the length or robustness of certain carpal features. Not all species plotted where they were expected to based on their locomotor category, so we cannot prove there is a significant correlation between morphology and behavior. Nor were the trends strong enough to prove a correlation between hand posture and carpal form. However, it is still possible these methods can be refined and utilized to infer behavior in fossil primates in the future.Item Open Access Encephalic Arterial Canals and Their Functional Significance(2020) Harrington, Arianna RoseA fundamental question in evolutionary anthropology asks how the human brain evolved. Characterized as relatively large and energetically taxing, numerous hypotheses have been proposed to explain how the human brain has evolved to its current size through tradeoffs to improve fitness by increasing behavioral complexity while minimizing caloric costs. The comparative method has been a key approach to testing these hypotheses, but a major hinderance has been the lack of directly measured brain metabolic rates for many comparable species. This dissertation takes an anatomical approach to predict brain metabolic rates from osteological specimens, utilizing the following proposed relationships: 1) that the brain is supplied by arteries (encephalic arteries) which travel through bony canals, 2) the size of the canal reflects the size of the artery within, 3) the size of the artery is proportional to blood flow rate, and 4) encephalic blood flow rate is proportional to brain metabolic rate.
Radii of encephalic arterial canals of a growth series of humans (n= 305 individuals) and of adult mammals (n=329 species) were measured from cadaveric computed tomography scans and osteological specimens, and blood flow rates were predicted using anatomical and physiological equations previously published in the literature. The major goals of this dissertation were to better evaluate the use of encephalic arterial canals in the prediction of brain metabolism and to characterize how mammals vary in their brain size, encephalic blood flow rates, brain metabolism, and whole body metabolism to test hypotheses which have been proposed to explain human and primate brain evolution.
The first research chapter finds that the blood flow rates predicted from the sizes of the encephalic arterial canals tracks the changes in brain metabolism during human growth. The second research chapter finds that patterns of variation in predicted blood flow rate, brain size, and body size across primates and other mammals suggest that predicted blood flow rates are reflecting the metabolic substrate supply needs of the brain. Furthermore, evidence is presented that the relative metabolic rate of the brains of primates is lower than many mammals of comparable brain size. The third research chapter utilizes phylogenetically informed Bayesian methods to predict brain metabolic rates from predicted blood flow rates, and finds that humans devote a high (although not always the highest) proportion of their basal metabolic rate (BMR) and total energy expenditure (TEE) to brain metabolism, even compared to other primates. In turn, primates tend to have elevated predicted brain metabolic rates relative to their BMR and TEE compared to most other mammal groups.
Combined, the evidence presented within this dissertation suggests that 1) osteologically derived predictions of blood flow rates present a viable alternative to understanding patterns of variation in brain metabolic rates during human ontogeny and among mammalian samples, and 2) compared to many other mammals, humans and other primates have evolved physiological mechanisms to reduce the mass-specific metabolic rate of their relatively large, energy-hungry brains.
Item Open Access Endocranial volume and shape variation in early anthropoid evolution(2014) Allen, Kari LeighFossil taxa are crucial to studies of brain evolution, as they allow us to identify evolutionary trends in relative brain size and brain shape that may not otherwise be identifiable in comparative studies using only extant taxa, owing to multiple events of parallel encephalization among primate clades. This thesis combines indirect and direct approaches to understanding primate evolution, by evaluating variation in the endocranial morphology of extant primates and their fossil representatives. I use a comparative approach to examine the relationships between interspecific adult endocranial volume and shape, and brain evolution and cranial form among extant primate clades and their fossil representatives. The associations are evaluated via phylogenetically informed statistics perfomed on volumetric measurements and three-dimensional geometric morphometric analyses of virtual endocasts constructed from micro-CT scans of primate crania. Fossil taxa included in these analyses are: 1) anthropoids Parapithecus, Aegyptopithecus (Early Oligocene, Egypt), Homunculus and Tremacebus (Early Miocene, Argentina), and 2) Eocene euprimates Adapis and Leptadapis (Eocene adapoids, France), and the Rooneyia (Eocene omomyoid, Texas).
The first part of this work (Chapter 2) explores variation in residual mass of brain components (taken from the literature) among primates, and evaluates the correlated evolution of encephalization and brain proportions with endocast shape, quantified via three-dimensional geometric morphometric techniques. Analyses reveal a broad range of variation in endocast shape among primates. Endocast shape is influenced by a complex array of factors, including phylogeny, body size, encephalization, and brain proportions (residual mass of brain components). The analysis supports previous research, which concludes that anthropoids and tarsiers (Haplorhini) share the enlargement of several key brain regions including the neocortex and visual systems, and a reduction of the olfactory system. Anthropoids further differ from strepsirrhines in endocranial features associated with encephalization--a more flexed brain base, an inferiorly deflected olfactory fossa--and those associated with brain proportions--a small olfactory fossa, and a more caudally extended cerebrum that extends posteriorly past the cerebellar poles. Tarsiers are unique in having a mediolaterally broad and rostro-caudally short endocast with an attenuated anterior and middle cranial fossae. This morphology is likely related to the extreme orbital enlargement in this taxon, which limits anterior expansion of the endocranium. Finally, despite the correlation between residual endocranial volume and endocast shape among modern primates, early anthropoid fossils demonstrate a disconnect between these factors in sharing key features of endocast shape with extant anthropoids at a relatively small brain size.
The second part of this thesis (Chapter 3) explores the relationship between craniofacial organization--cranial base angle, facial size, facial hafting--and encephalization via the lens of the Spatial Constraints and Facial Packing Hypotheses. These hypotheses predict that interspecific adult variation in encephalization correlates with endocranial shape such that a larger brain for a given body size will be more "globular" or spherical in shape. These hypotheses futher predict that basicranial angle covaries with encephalization and that the relative size of the endocranium and facial skeleton will have an antagonistic effect on basicranial angle and facial hafting. Results show that various measures of globularity have inconsistent and weak relationships to phylogeny, encephalization, and basicranial flexion, owing to a diversity of clade-specific scaling patterns between the maximum length, breadth, and width of the endocast. Among extant primates, there is weak but significant evidence to suggest that both facial size and encephalization influence variation in basicranial flexion. Considering the fossil specimens in isolation, their relative ranks in encephalization, basicranial flexion, and midline facial size and shape follow the pattern expected from the Spatial and Facial Packing Hypotheses outlined above; however, relative to modern species, the early fossil anthropoids have more flexed cranial bases and shorter facial skeletons at much smaller level of encephalization than seen in modern anthropoids.
Together, the extant data suggest a moderately conserved pattern of correlated evolution among endocranial size, endocranial shape, brain proportions, and craniofacial organization, which may explain differences in endocranial and facial shape between extant strepsirrhine and anthropoid primates; however, the fossil record for early anthropoid evolution demonstrates that a shift towards key anthropoid-like traits of the endocranium, basicranium, and facial skeleton were initiated early in anthropoid evolution, with subsequent encephalization occurring within and among members of this clade. Thus, these anthropoid cranial traits evolved in tandem with changes in the relative size of brain components, rather than absolute or relative brain size alone. Basicranial flexion, facial length and orientation are influenced by both: 1) shifts in endocranial shape associated with changes in brain proportion--accounting for the initiation of the anthropoid-like craniofacial plan early in the evolution of the clade--and 2) encephalization, which influenced subsequent morphological divergence among extant anthropoid groups.
Item Open Access Evidence of self-domestication in wild coyotes?(2017-12-01) Brooks, JamesWhile the evolution of cognition is still poorly understood, the self-domestication hypothesis proposes that psychology can evolve due to natural selection on temperament that leads to expanded developmental windows and cascading phenotypic effects. This hypothesis has been proposed to apply to dogs, bonobos, and even humans based on evidence for increased prosociality and a host of phenotypic traits resembling by-products of experimental domestication found in each species. To date all evidence in support of the self-domestication hypothesis has comes from experiments and inferred past selection pressure in wild animals. No study has tested for natural selection favouring increased prosociality in current populations of wild animals. In the past decades many animals have been rapidly recolonizing environments densely populated by humans. Urbanization is predicted to select for nonhumans that are non-aggressive, less fearful, and even attracted to densely populated areas and humans more generally. Coyotes represent an ideal candidate species to test this hypothesis as they have increasingly expand into new urban habitats. Coyote behaviour is likely influenced by human activity. They are displaying highly plastic behaviour in feeding and sleep patterns while they are hybridizing with other canids, and are undergoing these behavioural changes very rapidly relative to evolutionary time. As an exploratory test for signals of coyote self-domestication in areas of varying human influence, we used data from camera traps deployed across North Carolina. We coded coyote behaviour toward the camera (notice/approach) to test for changes in temperament associated with level of human density. Initial results suggest wild coyotes have a tendency to approach trap cameras less often in the most remote habitats than coyotes in exurban areas. Although the findings are not conclusive, they provide reason to further test for a link between differential coyote temperament and degree of urbanization. It also suggests the feasibility of using behaviour recorded by camera traps to test predictions generated by cognitive evolutionary theory. This initial research provides the first results consistent with self-domestication in modern species undergoing rapid evolution due to natural selection.Item Open Access Evolution of Gene Regulation in Papio Baboons(2019) Vilgalys, Tauras PatrickChanges in gene regulation are thought to play an important role in primate evolution and divergence. In support of this hypothesis, comparative evidence clearly demonstrate that gene expression patterns differ between closely related species and tend to evolve under selective constraint. However, we know little about the evolutionary forces that shape gene regulation across primates, particularly outside of humans and the other great apes. To address this gap, my dissertation draws on population and functional genomic variation between baboon species and within an admixed wild baboon population to address two themes: (i) how is gene regulatory divergence related to genetic divergence? and (ii) to what extent has natural selection shaped regulatory variation? Using interspecific comparative approaches, I show that changes in DNA methylation accumulate with increasing sequence divergence. While most changes in methylation can be explained by genetic drift, a subset are likely to have evolved under positive selection. Then, using genomic data from admixed baboons, I show that interspecific changes in DNA methylation are linked to genetic effects on DNA methylation (i.e., methylation quantitative trait loci, meQTL) and differences in allele frequency between baboon species. I also show that changes in DNA methylation are associated with changes in gene expression. Finally, I identify genomic evidence for selection against admixture in baboons, especially near genes that are differentially expressed between species. Together, my work highlights the close relationship between genetic and gene regulatory divergence in baboons. It also emphasizes the importance of natural selection in shaping genetic and regulatory variation throughout primate evolution, including in a living model for admixture in our own lineage.
Item Open Access Experimental Analyses of the Relationship Between Semicircular Canal Morphology and Locomotor Head Rotations in Primates(2010) Malinzak, Michael DavidReconstructing locomotor patterns from fossils is crucial for understanding the origins of primates and important transitions in various primate clades. Recent studies suggest that the semicircular canals of the inner ear provide evidence about locomotion. The canals sense rotational head accelerations and drive reflexes essential for normal movement. Because bony aspects of canal morphology influence canal sensitivity, this system can be studied in osteologic specimens and fossils. Variation in canal morphology in living and, by inference, extinct primates has been attributed to interspecific differences in locomotor behavior. However, the manner in which movement selects for canal morphology is debated, alternative scenarios are plausible, and no relevant measurements are available documenting head movements in primates.
To refine proposed links between canal morphology and locomotor function, and to resolve conflicting functional interpretations, this study examines head rotations in lemurs and lorises exhibiting diverse locomotor behaviors. Three-dimensional kinematic analyses were used to characterize angular velocities of the head during locomotion. These data are used to test hypotheses concerning intraspecific, interspecific, and body-size dependent variation in head rotations. Cranial CT scans are used to model canal sensitivity to rotations in different directions. Observed patterns of head rotation are compared to predicted patterns of sensitivity to test hypotheses about the relationship between locomotor behavior and canal design.
Evaluation of existing locomotor inferences reveals that brain size exerts a significant effect on canal size and that the prevailing equations for predicting agility from body and canal size are highly inaccurate. Intraspecific comparisons between maps of observed angular velocity and predicted sensitivity allow identification of map types associated with different general locomotor modes and do not support existing hypotheses about the primary selective forces acting on canal morphology. The new data are used to formulate and test a novel "fast-accurate hypothesis" to explain why all vertebrates are more sensitive to rotations about some axes than others. The fast-accurate hypothesis stipulates that angular velocities presented about axes of mean sensitivity are most accurately interpreted by the brain, and that selection aligns axes of mean sensitivity with axes of habitually fast rotation because accurate perception of rapid rotations confers survival benefit. The fast-accurate hypothesis was used to predict which features of the canals should be correlated with high mean angular velocities of head movement. Novel equations that predict behavior from these newly identified canal morphologies were generated and found to outperform existing equations when tested on the original sample of 11 strepsirrhine species.
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