Daniel Richter, Ph.D.
Institut de Biologia Evolutiva

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ABSTRACT
The Tara Oceans expedition circumnavigated the globe over a multi-year period, collecting samples in the sunlit ocean from over 150 individual stations. For eukaryotic plankton ranging from 0.8 μm-2 mm, three types of sequencing data were produced: metagenomes, metabarcodes of the 18S ribosomal locus, and metatranscriptomes. We present analyses that compare and contrast each data set. First, based on sequence similarity among metagenomes, we partition the oceans into regions inhabited by similar plankton communities. For smaller organisms, these regions are consistent with the provinces of Longhurst based on biogeochemical data, but this relationship breaks down above 20 μm. We find that large-scale transport by ocean currents plays a primary role in shaping plankton communities. Next, to measure the activity of these communities, we apply a phylogenetic read placement approach to map metatranscriptomic sequences onto a set of 300 conserved eukaryotic gene trees. We find that, globally, metabarcodes and metatranscriptomes show a similar representation of major eukaryotic lineages, indicating that both sources likely reflect the biomass of active cells in the surface ocean. Within the pico- and nanoplankton (0.8-5 and 5-20 μm), we find an unexpectedly high relative abundance of dinoflagellates and a substantial representation of transcriptionally active metazoans. We close with an example of the relationship between silicon concentration and global transcription of a specific gene, SIT, which transports extracellular silicon into organisms that construct silica-based structures, such as the frustules of diatoms and the loricae of choanoflagellates.

Host: Alberto Stolfi, Ph.D.

Nicole Hellessey, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

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ABSTRACT
Antarctic krill (Euphausia superba) is a key component of the Antarctic food web with considerable lipid reserves that are vital for both their own and higher predator survival. Krill feed on diatoms, dinoflagellates and other algal species year-round, resulting in high omega-3 polyunsaturated fatty acids which are essential for krill health, growth and reproduction. Krill-derived omega-3 containing products (particularly eicosapentacnoic acid (20:5w3) and docosahexaenoic acid (22:6w3)) are sold as nutraceuticals for human consumption. Krill oil tablets (sold as an omega-3 supplement) are now one of the fastest growing nutraceuticals globally. However, few attempts have been made to link the spatial and temporal variations in krill lipids to those in their food supply. Knowledge of krill diet and krill lipid dynamics is lacking for the Indian and Pacific Oceans, as most studies have focused on the South Atlantic Ocean sector where the krill fishery is based. Most research voyages are conducted during the summer and all scientific studies are restricted in their spatial and temporal scales. Another major gap in current Antarctic ecosystem models is the link between environmental drivers and their impact on primary production and therefore food availability. Satellite-derived data for biological and ecological measures is still developing as a tool although outputs such as ocean colour data which can be converted into chlorophyll a concentrations (a proxy for primary production), are becoming more common. This seminar will cover recent developments in the knowledge of spatiotemporal fluctuations of krill lipid biochemistry in relation to their environment.

Kai Ziervogel, Ph.D.
Institute for the Study of Earth, Oceans and Space
University of New Hampshire

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ABSTRACT
Marine snow aggregates are fast sinking vehicles of organic and inorganic matter that often form at the decline of a phytoplankton bloom, accelerating the vertical downward flux of biologically fixed atmospheric carbon to the deep ocean. Marine snow also incorporates and transports marine contaminants such as microplastics and spilled oil into the ocean’s interior. During sinking through the water column, aggregates are subject to biological and physical transformation, determining the export efficiency of marine snow-associated matter. I will present results from laboratory incubations on heterotrophic microbial degradation and physical fragmentation of marine snow and marine oil snow, emphasizing the importance of small scale processes in millimeter-sized aggregates on large scale implications for the ocean’s elemental cycling.

Audrey Sederberg, Ph.D.
Department of Physics
Emory University

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ABSTRACT
A central goal of neuroscience is to connect structure to function: to understand how neural activity and neuroanatomy control the actions, perception, and cognition of an organism. In recent years, there has been an explosion in the quantity and quality of neural data. Only ten years ago, recording simultaneously from a few dozen cells was notable, and now that number is in the thousands. We also know more about the intricacies of microcircuit anatomy, with detailed information on individual cell types and the patterns of connectivity among them. These data are exciting, but also raise challenging questions and require integrating precise, quantitative predictions into the analysis of large, complex datasets. In my talk, I will focus on two examples of how new directions in theoretical and data-analytic research can lead to novel insight into the function of neural circuits. First, I will show how minimally structured networks can capture many features of large-scale neural population recordings with surprising precision (within a few percent!), suggesting new approaches for linking structure to function. In the second part of the talk, I will show how we use prediction to extract essential features of a dynamic cortical state, a general approach that can be extended across brain areas and species to build a quantitative, comparative framework for the analysis of cortical dynamics. These are steps toward the ultimate goal of predicting, from the anatomy of a microcircuit, both the statistics of activity (e.g., selectivity, correlations, power spectra) that it generates and how that activity supports microcircuit computations relevant to behavior.

Joseph Lachance, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

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ABSTRACT
Human genomes have been shaped by natural selection, population bottlenecks, and archaic admixture. These evolutionary processes contribute to hereditary differences in disease risk across populations. Here, I explore how disease risk has changed over time and address some of the challenges of applying precision medicine approaches to diverse global populations. My lab’s research fits into four broad themes: anthropological genetics, analysis of ancient DNA, population genetics of prostate cancer in Africa, and improving the transferability of polygenic risk scores. By combining genetic data with mathematical models and computer simulations, we have been able to infer the complex demographic history of diverse human populations (including evidence of sex-biased admixture and interbreeding with unknown “ghost” populations). My lab has also applied precision medicine approaches to ancient human genomes and used time series data to infer the strength of natural selection acting on disease-associated alleles. Differences in risk allele frequencies across populations can contribute to health disparities, including elevated rates of aggressive cancer in men of African descent. Research in my lab has focused on the evolutionary causes of this health disparity and the development of a novel genotyping array that is optimized for detecting genetic associations with prostate cancer in sub-Saharan Africa. Finally, genetic predictions do not always generalize well across populations. To address this challenge, we leveraged evolutionary information to improve the transferability of polygenic risk scores.

This Town Hall is a follow up to the Science and Projections for our Return to Campus, held at the start of August. Professors Weitz and Gibson will explain the results of surveillance testing so far, share the need for ongoing vigilance and increased participation, and respond to questions from the community. Alexa Harter, CIPHER Director for GTRI, will also share information and answer questions about the NOVID app. Everyone is welcome! Join via BlueJeans Events. A recap of this talk will be posted to cos.gatech.edu.

Minoru Shinohara, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

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ABSTRACT
Human motor function is impaired with neurological disorders and injuries such as spinal cord injury and stroke. Among others, reduced neural excitability of the motor cortex and unintended co-activation of antagonistic (i.e. opposing) muscles are the major neurological problems associated with the impaired motor function. Conventional rehabilitation strategies of repeating motion practice have limitations in regaining neuromotor function in clinical populations. Hence, novel approaches are needed that can further facilitate neuromodulation and thereby rehabilitation outcome. By considering neurophysiological integration in humans, we have designed unique approaches: noninvasive perturbations to the autonomic nervous system (i.e., orthostatic stress, afferent vagus nerve stimulation) for modulating corticospinal excitability and motor control, paired stimulation of the afferent and efferent nervous systems for modulating corticospinal excitability, and anti-phasic co-activation practice for modulating common neuromotor oscillations during voluntary contraction and motor control. I plan to discuss our experimental studies that have examined the efficacy of these unique approaches in healthy adults. The fundamental findings on the efficacy in healthy individuals have laid the foundation for studying the application of the new interventions to clinical populations.

School of Biological Sciences professors Joshua Weitz and Greg Gibson will provide updates on Covid-19 projections and surveillance testing with a focus on the return to campus.

To join: https://primetime.bluejeans.com/a2m/live-event/jyyabssd