Collaborative Research: Morphology and Molecules: Diatom Diversification, Extinction, and Dispersal in an Ancient Tropical Lake System

合作研究：形态和分子：古热带湖泊系统中硅藻的多样化、灭绝和扩散Sherilyn Fritz和Paul Baker内布拉斯加-林肯大学和杜克大学特有动植物的起源，那些局限于特定地理区域的物种，一个多世纪以来一直吸引着自然科学家。地方性种群的演变归因于多个气候周期的栖息地稳定性，这在很长一段时间内促进了遗传多样性的建立，或者也归因于大规模干扰发生后的殖民和广泛辐射。因此，环境历史的不同轨迹(稳定与不稳定)被认为会带来更高水平的地方性和生物多样性。这个高度跨学科的项目将把来自沉积物岩心的化石数据与分子系统地理学结合起来，以测试关于热带安第斯山脉浮游硅藻的一个主要谱系--环藻和环藻复合体--的形态和遗传变异的幅度和速度的假说。我们将利用以前从玻利维亚/秘鲁的喀喀湖和智利的拉戈·春加采集的岩芯，研究过去~0.4My期间赤眼莲复合体形态变化和灭绝的微古生物学分析，并与在相同样本中分析的独立气候变化测量进行比较，以评估环境驱动因素在进化变化模式中的作用。该项目还将对安第斯高原的多个湖泊进行采样，以确定现代赤潮鱼种群的遗传组成，并评估种群之间的遗传变异，以推断种内进化历史(包括变异、扩散和基因流动)。如果流动是有限的，来自喀喀湖和拉戈春加的种群的遗传特征可以被用来为分子时钟方法提供信息，以得出关于多个种群遗传分化时间的假设。此外，将通过确定热带南美洲湖泊中环藻属所有成员的地理分布，将环藻复合体的历史置于更广泛的生物地理框架内。智慧的价值和更广泛的影响直接观察化石记录和当代种群的分子遗传特征是研究进化变化模式和速度的补充方法。然而，这两种方法很少被结合在一项单一的研究中，以调查多样化、扩散和灭绝。这个项目是高度跨学科的，并利用先前的大湖钻探计划产生的丰富框架来研究进化生物学。这项研究提出了一种创造性的模型，将新的分子遗传学方法与传统的古生物学和生物地理学工具联系起来，以研究微生物的进化过程，并将在这一令人兴奋的跨学科前沿培养研究生。此外，通过项目调查人员积极参与内布拉斯加州的教育和外联活动，K-12学生和其他公众将接触到地质学和分子遗传学的跨学科交叉。

Collaborative Research: Morphology and Molecules: Diatom Diversification, Extinction, and Dispersal in an Ancient Tropical Lake SystemSherilyn Fritz and Paul BakerUniversity of Nebraska-Lincoln and Duke UniversityThe origins of endemic floras and faunas, those that are restricted to a specific geographic area, have intrigued natural scientists for well over a century. The evolution of endemic groups has been attributed to habitat stability through multiple climate cycles, which fostered the build-up of genetic diversity through long periods of time, or alternatively to colonization and extensive radiation following episodes of massive disturbance. Thus, very different trajectories of environmental history (stability versus instability) have been posited to bring about higher levels of endemism and biodiversity. This highly interdisciplinary project will integrate fossil data from sediment cores with molecular phylogeography to test hypotheses about the magnitude and rate of morphological and genetic variation in a major lineage of planktonic diatom in the tropical Andes, the Cyclostephanos andinus complex. Micropaleontological analyses of morphological diversification and extinction in the C. andinus complex during the last ~0.4 my will be studied using cores collected previously from Lake Titicaca, Bolivia/Peru and Lago Chungará, Chile and compared with independent measures of climate variation analyzed in the same samples to assess the role of environmental drivers in the patterns of evolutionary change. The project also will sample multiple lakes in the Andean Altiplano to characterize the genetic composition of modern C. andinus populations and to assess genetic variation among the populations to infer intraspecific evolutionary histories (including vicariance, dispersal, and gene flow). If flow is limited, genetic characterization of populations from Lake Titicaca and Lago Chungará can be used to inform molecular clock methods to derive hypotheses about the timing of genetic divergences of multiple populations. In addition, the history of the C. andinus complex will be placed within a broader biogeographic framework by establishing the geographic distribution of all members of the genus Cyclostephanos in tropical South American lakes. Intellectual Merit and Broader ImpactsDirect observation of the fossil record and molecular genetic characterization of contemporary populations are complementary approaches for studying the patterns and rates of evolutionary change. Yet these two approaches have rarely been combined in a single study to investigate diversification, dispersal and extinction. This project is highly interdisciplinary and takes advantage of the rich framework generated by a prior large-lake drilling program to investigate evolutionary biology. The research presents a creative model for the linkage of new molecular genetic approaches with traditional paleontological and biogeographic tools to investigate evolutionary processes in microorganisms and will train a graduate student at this exciting interdisciplinary frontier. In addition, K-12 students and other members of the public will be exposed to this interdisciplinary intersection of geology and molecular genetics by the active engagement of project investigators in education and outreach activities in Nebraska.