Browsing by Subject "Zoology"

Now showing 1 - 4 of 4
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    The Origin of the Eosinophil Leucocytes of Mammals
    (1921) Ringoen, Adolph R.
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    Stress, Evolution, and Sociality in Wild Female Baboons
    (2008-05) Bosacker, Anna Lynn
    Organisms that successfully respond to threats have higher fitness than those who fail to mount appropriate responses. The vertebrate stress response system has evolved as a suite of physiological and behavioral strategies for coping with such threats, but chronic activation of this system can carry long-term physiological costs. I studied a population of wild olive baboons (Papio cynocephalus anubis) and used demographic and hormonal data to investigate how social parameters influence exposure to stressors and also to consider the adaptive value of the chronic stress response. Social circumstances such as rank and access to social support have been associated with differential exposure to the physiological costs of stress including exposure to the stress hormone, cortisol. I found that neither rank nor social support correlated significantly with cortisol exposure in adult female baboons. In contrast, a juvenile female’s social circumstances strongly influence her exposure to cortisol; maternal rank, a living mother, and the presence of multiple female kin were all significant predictors of cortisol exposure. I also considered the evolutionary history of the vertebrate stress response system. The system’s major weakness has always been believed to be its enigmatic predisposition for chronic and pathological activation. I propose that this tendency for continued activation in the face of lasting challenges can carry its own adaptive benefits and is not, as has been long assumed, merely maladaptive. In reaction to a severe and prolonged stressor, the baboons implemented a number of cortisol-mediated coping strategies, suggesting that sustained activation of the stress response system may promote lasting changes in behavior and physiology that can promote survival. Thus, the long-term risk of pathology may be outweighed by more immediate survival benefits.
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    Systematics, Biogeography, and Phylogeography of Thylamys Mouse Opossums, a Recent Radiation of Neotropical Marsupials
    (2013-08) Giarla, Thomas Christopher
    This project broadly explores the systematics, biogeography, and phylogeography of Thylamys mouse opossums, a genus of Neotropical marsupials from central and southern South America. Chapter 1 is part of a collaborative work with Robert Voss and Sharon Jansa (Chapter 1). In it, we resolve longstanding issues surrounding Thylamys taxonomy and nomenclature using mitochondrial DNA sequences and morphology, and provide the first phylogenetic hypothesis for all recognized species in this genus. We recognize nine species but also uncover numerous morphologically cryptic mitochondrial haplogroups within four species. In Chapter 2, I assess the evolutionary independence of a subset of these morphologically cryptic lineages within the montane species Thylamys pallidior, T. sponsorius, and T. venustus. I find evidence to support the existence of two lineages within each of the three species, and also conduct tests to determine the number of nuclear loci needed to confidently test species limits. In Chapter 3, I examine the biogeographic history of Thylamys and its monotypic sister-genus Lestodelphys, considering the impact of habitat type and physical barriers on range evolution and cladogenesis. In Chapter 4, I test predictions regarding the impact of late Quaternary glacial cycles on the evolutionary history of six montane cryptic lineages. I estimate divergence times and demographic shifts for each lineage, and find limited support for the core predictions. Two supplementary files are provided online as part of this dissertation: a file containing 15 phylogenetic trees for each of the loci considered in Chapter 2 (Online Supplementary File 1) and a file containing GenBank accession numbers and tissue voucher numbers for the sequences included in the supermatrix in Chapter 3 (Online Supplementary File 2).