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Description
The pattern and strength of genetic covariation is shaped by selection so that it is strong among functionally related characters and weak among functionally unrelated characters. Genetic covariation is expressed as phenotypic covariation within species and acts as a constraint on evolution by limiting the ability of linked characters to evolve independently of one another. Such linked characters are "constrained" and are expected to express covariation both within and among species. In this study, the pattern and magnitude of covariation among aspects of dental size and shape are investigated in anthropoid primates. Pleiotropy has been hypothesized to play a significant role in derivation of derived hominin morphologies. This study tests a series of hypotheses; including 1) that negative within- and among-species covariation exists between the anterior (incisors and canines) and postcanine teeth, 2) that covariation is strong and positive between the canines and incisors, 3) that there is a dimorphic pattern of within-species covariation and coevolution for characters of the canine honing complex, 4) that patterns of covariation are stable among anthropoids, and 5) that genetic constraints have been a strong bias on the diversification of anthropoid dental morphology. The study finds that patterns of variance-covariance are conserved among species. Despite these shared patterns of variance-covariance, dental diversification has frequently occurred along dimensions not aligned with the vector of genetic constraint. As regards the canine honing complex, there is no evidence for a difference in the pleiotropic organization or the coevolution of characters of the complex in males and females, which undermines arguments that the complex is selectively important only in males. Finally, there is no evidence for strong or negative pleiotropy between any dental characters, which falsifies hypotheses that predict such relationships between incisors and postcanine teeth or between the canines and the postcanine teeth.
ContributorsDelezene, Lucas (Author) / Kimbel, William H. (Thesis advisor) / Schwartz, Gary T (Committee member) / Spencer, Mark (Committee member) / Verrelli, Brian C (Committee member) / Arizona State University (Publisher)
Created2011
Description
This study examined the ontogeny of body mass (i.e. "growth") of Otolemur garnettii and Galago senegalensis. Growth is a proximate causal mechanism for adult size variation and growth patterns themselves can be the target of selection with adult size being the end result. Therefore, growth patterns of species can be the result of adaptation to species-specific social system, ecology, and life-history. The goals of this study were to: (1) Assess whether interspecific body mass variation was due to differences in growth rate, growth duration, a combination of the two, or neither; (2) test the hypothesis that sexual size dimorphism is attained by differences in relative growth rate as predicted by sexual selection theory; and (3) test the hypothesis that frugivorous O. garnettii grow at a relatively lower rate than gummivorous Go. senegalensis as predicted by an ecological risk aversion hypothesis. Growth rates and durations of Otolemur garnettii and Galago senegalensis males and females were compared both interspecifically and intraspecifically. The hypotheses regarding the ontogeny of sexual size dimorphism and the risk aversion hypothesis were not supported. O. garnettii males and females grow at an absolutely higher rate and for a longer duration compared to Go. senegalensis males and females respectively. O. garnettii females grow at a relatively higher rate compared to Go. senegalensis females as well. This may relate to weaning habits. O. garnettii infants are weaned during the dry season when feeding competition would be presumably high making large mass at weaning advantageous. While the growth of females might be strongly influenced by natural selection and competition for resources following weaning, the growth of males may be more strongly influenced by sexual selection relating to contest competition for females. Sexual size dimorphism results from differences in growth duration in O. garnettii and from differences in both growth duration and growth rate in Go. senegalensis. The results of this study highlight the need for more data on the growth patterns, mating and social systems, feeding competition, and life history schedules for these and other galagids. Study of how and why growth patterns have diverged through evolution is important in discerning the evolutionary history of each species.
ContributorsSchaefer, Melissa K (Author) / Nash, Leanne T. (Thesis advisor) / Marzke, Mary W. (Committee member) / Schwartz, Gary T. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Identifying the ecological role, or niche, that a species occupies within their larger community elucidates environmental adaptability and evolutionary success. This dissertation investigates the occupied niche of chimpanzees (Pan troglodytes schweinfurthii) living in an open, dry savanna-woodland environment by examining patterns of resource use and interspecific interactions. Data were collected October 2010--November 2011 at Issa, in the Ugalla region of western Tanzania, which is one of the driest, most open, and seasonal habitats inhabited by chimpanzees. Unlike most primatological studies which employ methods that include focal follows, this study focused instead on observing 'resource patches' for chimpanzees. Patch focals allow for the observation of all animals within a study area; capture resources that are not used by the study species; and are particularly well suited for unhabituated communities. In order to better understand relationships between environment and behavior, data collected at Issa are compared with published data from other chimpanzee populations. Issa chimpanzees were expected to have broader resource use than forest chimpanzees, as well as increased competition with other fauna, due to fewer available resources. However, in contrast to the assumption of food scarcity in dry habitats, dietary resources were available throughout the year. Like other populations, the diet of Issa chimpanzees consisted of mostly fruit, but unlike at other sites, the majority of plants consumed were woodland species. Additionally, although chimpanzees and other fauna shared spatial and dietary resources, there was only nominal overlap. These results point to extremely low levels of indirect competition between chimpanzees and other fauna. Despite extensive study of forest chimpanzees, little is known about their role within their faunal community in open, dry habitats, nor about how greater seasonality affects resource use. This project addresses both of these important issues and fosters novel approaches in anthropological studies, especially in reference to chimpanzee ecology and evolution. Understanding current chimpanzee behavioral relationships with their environments shapes hypotheses about their pasts, and also informs predictions about behaviors of similar taxa in paleo-environments. Lastly, examining the ecological role of chimpanzees within their larger communities will influence the formation of, as well as evaluate, conservation strategies.
ContributorsRussak, Samantha M (Author) / Reed, Kaye E (Thesis advisor) / Nash, Leanne T. (Committee member) / Schwartz, Gary T (Committee member) / Arizona State University (Publisher)
Created2013
Description
Extremely thick cranial vaults have been noted as a diagnostic characteristic of Homo erectus since the first fossil of the species was identified, but potential mechanisms underlying this seemingly unique trait have not been rigorously investigated. Cranial vault thickness (CVT) is not a monolithic trait, and the responsiveness of its layers to environmental stimuli is unknown. Identifying factors that affect CVT would be exceedingly valuable in teasing apart potential contributors to thick vaults in the Pleistocene. Four hypotheses were tested using CT scans of skulls of more than 1100 human and non-human primates. Data on total frontal, parietal, and occipital bone thickness and bone composition were collected to test the hypotheses: H1. CVT is an allometric consequence of brain or body size. H2. Thick cranial vaults are a response to long, low cranial vault shape. H3. High masticatory stress causes localized thickening of cranial vaults. H4. Activity-mediated systemic hormone levels affect CVT. Traditional comparative methods were used to identify features that covary with CVT across primates to establish behavior patterns that might correlate with thick cranial vaults. Secondly, novel experimental manipulation of a model organism, Mus musculus, was used to evaluate the relative plasticity of CVT. Finally, measures of CVT in fossil hominins were described and discussed in light of the extant comparative and experimental results. This dissertation reveals previously unknown variation among extant primates and humans and illustrates that Homo erectus is not entirely unique among primates in its CVT. The research suggests that it is very difficult to make a mouse grow a thick head, although it can be genetically programmed to have one. The project also identifies a possible hominin synapomorphy: high diploë ratios compared to non-human primates. It also found that extant humans differ from non-human primates in overall pattern of which cranial vault bones are thickest. What this project was unable to do was definitively provide an explanation for why and how Homo erectus grew thick skulls. Caution is required when using CVT as a diagnostic trait for Homo erectus, as the results presented here underscore the complexity inherent in its evolution and development.
ContributorsCopes, Lynn (Author) / Kimbel, William H. (Thesis advisor) / Schwartz, Gary T (Committee member) / Spencer, Mark A. (Committee member) / Ravosa, Matthew J. (Committee member) / Arizona State University (Publisher)
Created2012
Description
Unanswered questions about the evolution of human gender abound and are salient across the anthropological disciplines and beyond. Did adult sex-typed behavioral tendencies actually evolve? If so, when? For what purpose? The best way to gain insight into the evolution of human gender is to understand the evolution and development of sex-typed behavior in comparative primate taxa. Captive research indicates that there are many proximate factors likely to shape the development of sex-typed behavior in non-human primates—prenatal and postnatal endocrinological experience, social experience, ecological factors, and their interactions. However, it is largely unknown how sex-typed behavior proceeds and is shaped by those factors in evolutionarily salient environments. This study investigated one—whether extrinsic sexually differentiated social interactions are likely influential in the development of adult sex-typed behavior in wild-living Lemur catta. Little is known about sex-typed development in this species or in strepsirrhines in general. This research therefore addresses an important phylogenetic gap in our understanding of primate sex-typed development. Behavioral observations were carried out on mixed cross-sectional sample of adult females (n=10), adult males (n=8), yearling females (n=4), yearling males (n=4), and newborn females (n=16) and males (n=14) at Beza Mahafaly Special Reserve in southwest Madagascar from September 2008 to August 2009. Twenty-three sex-typed behaviors were identified in adults using linear mixed effects models and models of group response profiles through time. Of those, only eight had a pre-pubertal developmental component. Infants did not exhibit any sex differences in behavior, but juveniles (prepubertal, weaned individuals) resembled adults in their (relatively few) patterns of expression of sex-typed behavior. Most adult sex-typed behaviors in this species apparently develop at or after puberty and may be under gonadal hormone control. Those that develop before puberty do not likely depend on extrinsic sexually differentiation social interactions for their development, because there is no clear evidence that infants and juvenile male and females are not treated differently by others according to sex. If sexually differentiated social interactions are important for sex-typed behavioral development in subadult ,italic>Lemur catta, they are likely intrinsically (rather than extrinsically) driven.
ContributorsMeredith, Stephanie Lynn (Author) / Nash, Leanne T. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Arizona State University (Publisher)
Created2012
Description
Fundamental hypotheses about the life history, complex cognition and social dynamics of humans are rooted in feeding ecology - particularly in the experiences of young animals as they grow. However, the few existing primate developmental data are limited to only a handful of species of monkeys and apes. Without comparative data from more basal primates, such as lemurs, we are limited in the scope of our understanding of how feeding has shaped the evolution of these extraordinary aspects of primate biology. I present a developmental view of feeding ecology in the ring-tailed lemur (Lemur catta) using a mixed longitudinal sample (infant through adult) collected at the Beza Mahafaly Special Reserve in southwestern Madagascar from May 2009 to March 2010. I document the development of feeding, including weaning, the transition to solid food, and how foods are included in infant diets. Early in juvenility ring-tailed lemurs efficiently process most foods, but that hard ripe fruits and insects require more time to master. Infants and juveniles do not use many of the social learning behaviors that are common in monkeys and apes, and instead likely rely both on their own trial and error and simple local enhancement to learn appropriate foods. Juvenile ring-tailed lemurs are competent and efficient foragers, and that mitigating ecological risks may not best predict the lemur juvenile period, and that increases in social complexity and brain size may be at the root of primate juvenility. Finally, from juvenility through adulthood, females have more diverse diets than males. The early emergence of sex differences in dietary diversity in juvenility that are maintained throughout adulthood indicate that, in addition to reproductive costs incurred by females, niche partitioning is an important aspect of sex differential feeding ecology, and that ontogenetic studies of feeding are particularly valuable to understanding how selection shapes adult, species-typical diets. Overall, lemur juvenility is a time to play, build social relationships, learn about food, and where the kernels of sex-typical feeding develop. This study of the ontogeny of feeding ecology contributes an important phylogenetic perspective on the relationship between juvenility and the emergent foraging behaviors of developing animals
ContributorsO'Mara, Michael Teague (Author) / Nash, Leanne T. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Sauther, Michelle L (Committee member) / Arizona State University (Publisher)
Created2012
Description
Mammals with a habitually orthograde trunk posture possess a more anterior foramen magnum than mammals with non-orthograde trunk postures. Russo & Kirk (2013) also found that bipedal orthograde mammals possess a more anteriorly placed foramen magnum than those that are just habitually orthograde. This finding has allowed us to use foramen magnum position as a predictor of trunk posture in early hominins. This prompts more research of how the other landmarks on the cranial base move in relation to this shift in foramen magnum positioning. I collected landmark data on images of 125 mammalian basicrania spanning 41 species that differed in trunk posture. Using Procrustes and Principal Components Analysis (PCA), I attempted to evaluate the effects of trunk posture on basicranial morphology, primarily focusing on the placement of the carotid and jugular foramina. The results supported Russo and Kirk's finding of a more anterior foramen magnum placement in orthograde mammals; in addition, the results displayed correlations between foramen magnum position and carotid foramen position among primates and diprotodonts.
ContributorsPena, Angela (Author) / Kimbel, William (Thesis director) / Schwartz, Gary T. (Committee member) / Barrett, The Honors College (Contributor) / School of Human Evolution and Social Change (Contributor)
Created2015-05
Description
Early hominins present an unusual pattern of sexual dimorphism. On one hand, the canine teeth of these species are weakly size-dimorphic, vertically short, and nonhoning, suggesting a social system characterized by infrequent, low-intensity intermale competition and monogamous pair-bonding. On the other hand, marked size variation in skeletal remains attributed to species of Australopithecus is thought to reflect strong body-mass dimorphism, which is more consistent with intense intermale competition. Reconciling these conflicting signals and understanding their adaptive significance is a major goal of paleoanthropology. This dissertation research contributes to this objective by investigating factors that may constrain or reduce canine height in extant anthropoid primates. Two hypotheses regarding the relationship between canine height and other elements of the masticatory system were tested using phylogenetic comparative methods. According to the first hypothesis, canine reduction is a pleiotropic by-product of changes in the sizes of other components of the dentition. With respect to canine height, the results of this study fail to support this idea. There is limited evidence for a relationship between basal canine crown dimensions and incisor and postcanine size, but significant interspecific correlations between these variables are not strong and are restricted primarily to the female maxillary dentition. These results indicate that if pleiotropy influences canine size, then its effects are weak. The second hypothesis proposes that canine reduction is a consequence of selection for increased jaw-muscle leverage. This hypothesis receives some support: there is a clear inverse relationship between canine height and the leverage of the masseter muscle in male anthropoids. Females do not exhibit this association due to the fact that dimorphism in muscle leverage is weak or absent in most anthropoid species; in other words, female muscle leverage tracks male muscle leverage, which is linked to canine height. Leverage of the temporalis muscle is not correlated with canine height in either sex. Two specimens of the 3.0-3.7-million-year-old hominin Australopithecus afarensis fall at or beyond the upper end of the great ape range of variation in masseter leverage, which is consistent with the idea that hominin canine evolution was influenced by selection for increased jaw-muscle leverage.
ContributorsScott, Jeremiah Ezekiel (Author) / Kimbel, William H. (Thesis advisor) / Schwartz, Gary T. (Committee member) / Spencer, Mark A. (Committee member) / Arizona State University (Publisher)
Created2010
Description
The bony pelvis is a pivotal component of the locomotor system, as it links the hindlimb with the trunk and serves as anchorage for the primary propulsive musculature. Its shape is therefore expected to be adapted to the biomechanical demands of habitual locomotor behavior. However, because the relationship between locomotor mechanics and pelvic morphology is not well understood, the adaptive significance of particular pelvic traits and overall pelvic shape remains unclear. This study used an integrative, dual approach to elucidate the relationship between form and function in the primate pelvis. A biomechanical cylinder model of pelvic stress resistance was tested using in vitro strain analysis of monkey and ape cadaver specimens. These results were used to refine adaptive hypotheses relating pelvic form to locomotor mechanics. Hypotheses of adaptation were then tested via univariate and geometric morphometric methods using a taxonomically broad, comparative sample of 67 primate taxa. These results suggest that the pelvis exhibits some iliac and ischial adaptations to stress resistance that are associated with the biomechanical demands of habitual locomotor loading and of body size. The ilium and ischium exhibit relatively low levels of strain during experimental loading as well as adaptations that increase strength. The pubis exhibits relatively high strains during loading and does not vary as predicted with locomotion. This integrated study clarifies the relationship between strain and adaptation; these results support the hypothesis that bones adapted to stress resistance exhibit low strains during typical loading. In general, the cylinder model of pelvic biomechanics is unsupported. While the predictions of loading regimes were generally rejected, the inability of these methods to test the possible occurrence of overlapping loading regimes precludes outright rejection of the cylinder model. However, the lack of support for predicted global responses to applied loading regimes suggests that pelvic stress resistance may be better explained by a model that accounts for local, functional subunits of pelvic structure. The coalescence of a localized model of pelvic biomechanics and comparative morphometrics has great potential to shed light on the evolution of the complex, multi-functional structure of the pelvis.
ContributorsLewton, Kristi Lynn (Author) / Spencer, Mark A. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Ward, Carol V. (Committee member) / Arizona State University (Publisher)
Created2010
Description
Skeletal diseases related to reduced bone strength, like osteoporosis, vary in frequency and severity among human populations due in part to underlying genetic differentiation. With >600 disease-associated mutations (DAMs), COL1a1, which encodes the primary subunit of type I collagen, the main structural protein in bone, is most commonly associated with this phenotypic variation. Although numerous studies have explored genotype-phenotype relationships with COL1a1, surprisingly, no study has undertaken an evolutionary approach to determine how changes in constraint over time can be modeled to help predict bone-related disease factors. Here, molecular population and comparative species genetic analyses were conducted to characterize the evolutionary history of COL1a1. First, nucleotide and protein sequences of COL1a1 in 14 taxa representing ~450 million years of vertebrate evolution were used to investigate constraint across gene regions. Protein residues of historically high conservation are significantly correlated with disease severity today, providing a highly accurate model for disease prediction, yet interestingly, intron composition also exhibits high conservation suggesting strong historical purifying selection. Second, a human population genetic analysis of 192 COL1a1 nucleotide sequences representing 10 ethnically and geographically diverse samples was conducted. This random sample of the population shows surprisingly high numbers of amino acid polymorphisms (albeit rare in frequency), suggesting that not all protein variants today are highly deleterious. Further, an unusual haplotype structure was identified across populations, but which is only associated with noncoding variation in the 5' region of COL1a1 where gene expression alteration is most likely. Finally, a population genetic analysis of 40 chimpanzee COL1a1 sequences shows no amino acid polymorphism, yet does reveal an unusual haplotype structure with significantly extended linkage disequilibrium >30 kilobases away, as well as a surprisingly common exon duplication that is generally highly deleterious in humans. Altogether, these analyses indicate a history of temporally and spatially varying purifying selection on not only coding, but noncoding COL1a1 regions that is also reflected in population differentiation. In contrast to clinical studies, this approach reveals potentially functional variation, which in future analyses could explain the observed bone strength variation not only seen within humans, but other closely related primates.
ContributorsStover, Daryn Amanda (Author) / Verrelli, Brian C (Thesis advisor) / Dowling, Thomas E (Committee member) / Rosenberg, Michael S. (Committee member) / Stone, Anne C (Committee member) / Schwartz, Gary T (Committee member) / Arizona State University (Publisher)
Created2010