A Study of Respiratory Turbinal Morphology in Response to Evolutionary Pressure and Development
Although the respiratory turbinals are structures which have long been known to function in heat and water recovery during nasal respiration, the role of natural selection and development in influencing the morphology of these specific turbinals have not been well-studied. With the aid of modern techniques such as computed tomography (CT scanning) and fluid flow models as well as histological analysis, we are now able to quantify and describe the function of respiratory turbinals to a greater degree than ever before. In this dissertation, we examine the morphology and functional significance of the respiratory turbinals at the individual, intraspecific, and interspecific levels. In chapter 1, the constraints of external skull morphology on turbinal form are examined using histological analysis and fluid models, with the goal of challenging conventional assumptions of what structures constitute the respiratory turbinals. In chapter 2, we compared two populations of a single species of deer mice, in order to assess the plasticity of respiratory turbinals in response to local environmental stress; here, high altitude and concurrent temperature and water stress. As respiratory turbinals are known to vary across species but not within species (in mammals), this chapter offers a first look at the plastic nature of respiratory turbinal development. Finally, in chapter 3, we address the question of whether there is a potential convergence upon an optimum respiratory turbinal size across distantly related phylogenetic groups. To answer this question, we quantified and compared relative respiratory turbinal size in ungulates and carnivorans, which have been previously known to have significantly different turbinal morphology. Further, we also assess the impact of diet on respiratory turbinal morphology within ungulates, as there are different degrees of water stress associated with dietary types. In summary, this dissertation demonstrates that at both the intraspecific and interspecific level, respiratory turbinal morphology in mammals is significantly influenced by lineage-independent factors such as environment stress, as well as lineage-dependent factors such as external skull morphology and diet.