Dissertation Research: Molecular Systematics and the Evolution of a Novel Red Blood Cell Morphology in Plethodontid Salamanders

拟议的研究将集中在不同层次的进化的多维分析，从分子到有机体和系统发育。 研究的生物体是Batrachoseps属的plethodontid蝾螈，在脊椎动物中是独一无二的，它在循环血液中的红细胞比例上表现出很大的变化-从几乎所有的有核到几乎所有的无核。 这种变化似乎与有机体专业化程度，特别是与伸长，衰减和小型化，在一组专门为semifossorial存在于季节性干燥的环境中的生物。 一个复杂的因素是这些生物体中非常高的基因组大小，这增加了一种可能性，即去核是一种与大细胞（大基因组的必要相关物）和小血管（小型化的必要相关物）之间的根本冲突相关的现象。 该研究将通过进行生态学和形态学研究来调查去核是小型化的机械结果的可能性。 为了继续下去，将有必要发展一个强大的系统发育假说属，使用分子标记。 线粒体基因已经被研究过了，系统发育树的许多尖端都有很好的分辨率;新的工作将集中在更保守的核基因和树中更深的分支上。 系统发育假说将允许对这一问题领域进行比较生物学分析，并确定小型化谱系中体型的增加是否伴随着红细胞成核水平的增加。这项研究的意义在于集中精力研究不同层次的组织--分子、细胞、有机体、生态、和系统发育--在发育过程中相互作用，为生物体的谱系提供形式和物质。 同时调查不同的水平提供了一个现实的评估如何通过时间在血统的进化进行，并允许一般适应过程的性质及其影响的评估。 这项研究还有望为研究基因组大小增加这一令人困惑的现象开辟新的途径，这在这些生物体中如此之大，以至于强烈影响细胞和生物体水平（经典的C值悖论）。

The proposed research will focus on a multidimensional analysis of evolution at different hierarchical levels, from the molecular to the organismal and phylogenetic. The study organisms, plethodontid salamanders of the genus Batrachoseps, are unique among vertebrates in displaying great variation in the proportion of red blood cells in the circulating blood - from nearly all nucleated to nearly all enucleated. The variation appears to be correlated with degree of organismal specialization, in particular with elongation, attenuation, and miniaturization, in a group of organisms that is specialized for semifossorial existence in seasonally dry environments. A complicating factor is the very high genome sizes in these organisms, which raises the possibility that enucleation is a phenomenon associated with a fundamental conflict between large cells, a necessary correlate of large genomes, and small blood vessels, a necessary correlate of miniaturization. The study will investigate the possibility that enucleation is a mechanical outcome of miniaturization, by conducting ecological and morphological studies. In order to proceed it will be necessary to develop a robust phylogenetic hypothesis for the genus, using molecular markers. Mitochondrial genes have already been studied, and there is good resolution of many of the tips of the phylogenetic tree; new work will focus on more conservative nuclear genes and deeper branches in the tree. A phylogenetic hypothesis will permit a comparative biological analysis of this problem area and a determination of whether increases in body size within a miniaturized lineage are accompanied by increases in nucleation levels for red blood cells.The significance of this research lies in the focused effort to study how different levels of organization -- molecular, cellular, organismal, ecological, and phylogenetic -- interact during development to give form and substance to lineages of organisms. A simultaneous investigation of different levels provides a realistic assessment of how evolution proceeds in lineages through time, and permits an assessment of the nature of general adaptation processes and their implications. The study also holds promise for opening new avenues of research on the puzzling phenomenon of increases in genome size, which are so great in these organisms as to strongly effect cellular and organismal levels (the classic C-value paradox).