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：古代热带湖泊系统中硅藻的多样化、灭绝和扩散内布拉斯加州大学林肯分校和杜克大学地方性动植物的起源，那些局限于特定地理区域的植物和动物，一个多世纪以来一直引起自然科学家的兴趣。地方性种群的进化可归因于多个气候周期中的栖息地稳定性，这在很长一段时间内促进了遗传多样性的积累，或者归因于大规模干扰事件后的殖民化和广泛辐射。因此，环境历史的非常不同的轨迹（稳定与不稳定）被假定为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沉积物岩心的化石数据与分子系统地理学结合起来，以检验热带安第斯山脉浮游硅藻主要谱系的形态和遗传变异的幅度和速率的假设，即环stephanos和inus复合体。本文将利用先前在玻利维亚/秘鲁的的的喀喀湖和智利的忠加湖<e:1>采集的岩心，对近0.4年C. andinus复群形态多样化和灭绝的微古生物学分析进行研究，并与在同一样品中分析的气候变化的独立测量结果进行比较，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，以表征现代C. andinus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）。如果流量有限，来自的的喀喀湖和忠加湖<e:1>种群的遗传特征可以用来为分子钟方法提供信息，以得出关于多个种群遗传分歧时间的假设。此外，通过确定环stephanos属所有成员在南美洲热带湖泊中的地理分布，将C. andinus复合体的历史置于更广泛的生物地理框架内。智力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的模式和速度的互补方法。然而，这两种方法很少被结合在一个单一的研究中来调查多样化、分散和灭绝。该项目是高度跨学科的，并利用了先前大型湖泊钻探计划产生的丰富框架来研究进化生物学。该研究提出了一个创造性的模式，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，研究微生物的进化过程，并将在这个令人兴奋的跨学科前沿培养研究生。此外，K-12学生和其他公众成员将接触到地质学和分子遗传学的跨学科交叉，通过项目调查人员积极参与在内布拉斯加州的教育和推广活动。

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.