MOLECULAR AND DEVELOPMENTAL APPROACH TO TWO MAJOR TRANSITIONS IN DIATOM EVOLUTION.

硅藻(微小的海洋植物)在生态上和经济上都非常重要(我们每五分之一的呼吸中的氧气来自硅藻)(有些会产生对人类有害的神经毒素)。它们也是物种最丰富的微藻类群(约20万种)--因此可以与陆地上开花植物的丰富性和多样性相媲美。在进化上，像开花植物一样，硅藻也是相对较新的物种，表明物种形成率很高。然而，与开花植物不同，硅藻物种形成的机制(S)尚不清楚。我研究的长期目标是评估硅藻性别和相关结构的进化意义，并更好地了解自侏罗纪化石记录中首次出现硅藻以来，各种类型的性别在硅藻物种多样性中所起的作用。这一提议的近期目标是对处于关键进化地位的两个主要硅藻谱系的代表应用发育和分子方法：基生非极着丝点(硅藻系统发育中最早的分支)和基生蛛形羽状藻类(衍生最多的硅藻--羽状硅藻分裂得最深)。我们将使用手头已有的克隆培养物，并从当地和遥远的地理位置建立更多的克隆培养物，以建立这些品系的健壮和密集采样的“系谱”(系统发育图)。我们将使用先进的显微技术(荧光和去卷积光学显微镜、扫描电子显微镜、X射线显微分析、二氧化硅特定染色)来检测和定位乳白色二氧化硅(硅藻细胞壁的构建块)，并描述其发育阶段细胞壁组件的精细结构。确定交配亲和性和性行为表达(例如，单性、多性)将提供对羽毛之间内外繁殖倾向的新见解，从而有助于预测这些硅藻的种内和种间遗传变异性，并最终对硅藻物种形成机制进行可检验的预测。对硅藻性别结构和交配行为的研究结果将被整合到通过分析选定的DNA序列描绘的硅藻类群的系统发育中。对这些硅藻的系统发育分析与我们在这里提出的比较发育方法相结合，是硅藻进化生物学中的新方法，我们在大约10年前才开创了这一领域。进一步发展的主要障碍是缺乏可重复的性诱导方案，而我们现在已经为所涉及的硅藻群体制定了这种方案。这项工作的结果将提供一个多管齐下的框架，以更好地理解硅藻的主要进化转变，并使我们能够在生物学(性别亲和性)和分子水平上表征物种边界。拟议的工作包括许多新的培训机会，包括面向本科生研究人员和更高级学生的高级显微镜和系统发育项目。

Diatoms (microscopic marine plants) are tremendously important ecologically (the oxygen in every fifth breath we take comes from diatoms) and economically (some produce neurotoxins harmful to humans). They are also the most species rich group of microalgae (~200,000 species) – thus rivalling the richness and diversity of flowering plants on land. Evolutionarily, like flowering plants, diatoms also are relatively new arrivals, suggesting a high rate of speciation. Unlike flowering plants, however, the mechanism(s) of speciation in diatoms is unknown.The long term objective of my research is to evaluate the evolutionary significance of diatom sex and related structures, and to better understand what role various types of sexuality play in the spectacular diversification of diatoms since their first appearance in the Jurassic Period fossil record. The immediate objectives specific to this proposal are to apply developmental and molecular approaches to representatives of two major lineages of diatoms in key evolutionary positions: the basal non-polar centrics (earliest branches in diatom phylogeny) and basal araphid pennates (deepest split among the most derived diatoms, the pennates). We will use monoclonal cultures already at hand and establish many more from local and distant geographies to develop robust and densely sampled “family trees” (phylogenies) for these lineages.We will use advanced microscopical techniques (epifluorescence and deconvolution light microscopy, scanning electron microscopy, x-ray microanalysis, silica-specific stains) to detect and localise opaline silica (the building blocks of diatom cell walls) and describe the fine structure of the cell-wall components during their stages of development. Determination of mating compatibility and behavioural expression of sex (e.g., unisexual, polysexual) will provide new insights into the propensity for in- vs. out-breeding among the pennates, thereby facilitating predictions about the intra- and interspecific genetic variability of these diatoms, and ultimately testable predictions about mechanisms of diatom speciation. Results from this study of diatom sexual structures and mating behaviour will be integrated into phylogenies of the diatom groups delineated by analysis of selected DNA sequences.Phylogenetic analysis of these diatoms combined with comparative developmental approaches we propose here are novel in diatom evolutionary biology, which we pioneered only about decade ago. The major obstacle to further advancement was the lack of reproducible sex-induction protocols which we now have for the diatom groups involved. The results of this work will provide a multipronged framework to better our understanding of major evolutionary transitions in diatoms and allow us to characterize species boundaries at a biological (sex-compatibility) and molecular level. The proposed work includes numerous new training opportunities, including advanced microscopy and phylogenetic projects for undergraduate researchers and more advanced students.