Sherilyn Fritz and Paul Baker University of Nebraska-Lincoln and Duke University
The 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 Impacts Direct 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.
