Graduate Research in Education: Learning the Research Story Through the Story of a Slow Cat

This book is designed to facilitate understanding of education research and guide the development and the writing of a research project. In education, like other social sciences, we are investigating issues directly involving or influencing humans. Research involving humans can be a complex and awkward endeavor. However, if we view this endeavor through the lens of a research story, we find a familiar genre we can relate to and understand. This concise, open textbook weaves the story of a cat throughout to explain the research components of typical education research projects.https://scholars.fhsu.edu/all_oer/1006/thumbnail.jp

Seasonal Variability in Diazotroph Abundance and Gene Expression at a Coastal N\u3csub\u3e2\u3c/sub\u3e Fixation Hotspot (Outer Banks, NC)

Marine microbial dinitrogen (N2) fixation, the conversion of gaseous N2 to bioavailable species, is the primary source of new oceanic nitrogen (N). N is present in nucleic acids, amino acids, and proteins, and is essential to all life. Long considered to be a primarily oligotrophic ocean process, significant N2 fixation rates have recently been observed in coastal environments, including along the Cape Hatteras front. To see if elevated N2 fixation was a persistent feature in this region, N2 fixation rates and N2 fixer (diazotroph) abundance and gene expression were investigated through roughly monthly sampling at a field station (Jennette’s Pier) in the Outer Banks, NC, from June 2019 to August 2020, as well as a day-long cruise around the pier in August of 2019. In addition to rate and molecular samples, chlorophyll, and particulate N samples were collected and salinity/temperature profiles were measured. Using quantitative polymerase chain reaction techniques, we investigated the abundance and gene expression of diazotrophic (N2 fixing) cyanobacteria possibly responsible for these high coastal rates, and compared these results to N2 fixation rates measured using a variant of the 15N2 tracer assay. Diazotroph species investigated include Trichodesmium spp. and 5 endosymbiont cyanobacteria. Preliminary results suggest evidence of Gulf Stream intrusions within 300m from the shore, and a seasonal variability pattern of nitrogen fixation rates. This study provides useful measurements of coastal N inputs in the context of the global ocean N cycle and budget, and explores chemical and physical factors that affect these processes.https://digitalcommons.odu.edu/gradposters2021_sciences/1009/thumbnail.jp

Defining the Environmental Niche of the Two Main Clades of \u3ci\u3eTrichodesmium\u3c/i\u3e: A Study on the West Florida Shelf

Dinitrogen (N2) fixation is the process of taking widely abundant but mostly biologically inaccessible N2 gas and converting it into more biologically accessible forms of the essential macronutrient nitrogen. Only a small fraction of organisms known as diazotrophs can perform biological N2 fixation. Trichodesmium is one such genus of N2-fixing marine cyanobacteria that is commonly observed in waters along the West Florida Shelf (WFS). We hypothesize that the two main Trichodesmium clades (T. erythraeum and T. thiebautii) occupy distinct environmental niches, one being more coastal and one being more oceanic. To test this hypothesis, we quantified gene abundance of both clades and compared the results with hydrographic data to distinguish any trends in niche distribution in samples collected on the WFS from three separate cruises. T. thiebautii abundance was higher further from the coast (at stations with greater bottom depths) and the T. erythraeum abundance was higher closer to the coast (at stations with lower bottom depths). A lack of nearshore sampling in 2015 initially made it difficult to conclusively identify trends in niche distribution, however with the addition of 2018 and 2019 samples, we observed a consistent coastal vs. open ocean niche separation for the two clades. In addition, T.thiebautii abundance was also significantly positively correlated with salinity. While previous work has found T. thiebautii is more abundant than T. erythraeum in open ocean surface waters, this is the first study to examine Trichodesmium clade abundance in a near-shore environment.https://digitalcommons.odu.edu/gradposters2021_sciences/1010/thumbnail.jp

Margalefidinium polykrikoides Cyst Resuspension in the Lafayette River, a Sub-tributary of the Chesapeake Bay

Harmful Algal Blooms are a collection of algae in a body of water that can cause serious environmental issues and health problems in both people and aquatic organisms. Dinoflagellates are microscopic, unicellular, and eukaryotic organisms that are well known for forming harmful algal blooms because of eutrophication. Coastal Virginia suffers from HABs in the Chesapeake Bay and its tributaries. A common species of dinoflagellate, known as Margalefidinium polykrikoides exists in the Chesapeake Bay. The purpose of this study is to determine if sediment resuspension produced by wind generated surface gravity waves cause cysts (dinoflagellate resting stages) to be suspended into the water column, which could contribute to bloom initiation if they germinate and then inoculate the water column with motile cells. Using light microscopy and qPCR, we will determine the percentage of resuspended dinoflagellate cysts being identified as Margalefidinium polykrikoides

Examining Ecological Succession of Diatoms in California Current System Cyclonic Mesoscale Eddies

The California Current System is a diatom-dominated region characterized by seasonal coastal upwelling and additional elevated mesoscale activity. Cyclonic mesoscale eddies in the region trap productive coastal waters with their planktonic communities and transport them offshore with limited interaction with surrounding waters, effectively acting as natural mesocosms, where phytoplankton populations undergo ecological succession as eddies age. This study examines diatom community composition within two mesoscale cyclonic eddies that formed in the same region of the California Current System 2 months apart and in the California Current waters surrounding them. The diatom communities were analyzed in the context of shifting environmental gradients and through a lens of community succession to expand our understanding of biophysical interactions in California Current System cyclonic eddies. Diatom communities within each eddy were different from non-eddy communities and varied in concert with salinity and dissolved iron (Fe) concentrations. The younger, nearshore eddy displayed higher macronutrient and dissolved Fe concentrations, had higher values for diatom Shannon diversity and evenness, and had nutrient ratios indicative of either eventual silicic acid (Si) or Fe limitation or possibly co-limitation. The older, offshore eddy displayed low macronutrient and dissolved Fe concentrations, was likely nitrate-limited, and had lower diatom Shannon diversity and evenness indices. Sequences from the genus Rhizosolenia, some of which form vertically migrating mats to bypass nitrate limitation, dominated in the older eddy. This is of potential significance as the prevalence of Rhizosolenia mats could impact estimates of carbon cycling and export in the wider California coastal area

High rates of N-2 fixation in temperate, western North Atlantic coastal waters expand the realm of marine diazotrophy

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mulholland, M. R., Bernhardt, P. W., Widner, B. N., Selden, C. R., Chappell, P. D., Clayton, S., Mannino, A., & Hyde, K. High rates of N-2 fixation in temperate, western North Atlantic coastal waters expand the realm of marine diazotrophy. Global Biogeochemical Cycles, 33(7), (2019): 826-840, doi:10.1029/2018GB006130.Dinitrogen (N2) fixation can alleviate N limitation of primary productivity by introducing fixed nitrogen (N) to the world's oceans. Although measurements of pelagic marine N2 fixation are predominantly from oligotrophic oceanic regions, where N limitation is thought to favor growth of diazotrophic microbes, here we report high rates of N2 fixation from seven cruises spanning four seasons in temperate, western North Atlantic coastal waters along the North American continental shelf between Cape Hatteras and Nova Scotia, an area representing 6.4% of the North Atlantic continental shelf area. Integrating average areal rates of N2 fixation during each season and for each domain in the study area, the estimated N input from N2 fixation to this temperate shelf system is 0.02 Tmol N/year, an amount equivalent to that previously estimated for the entire North Atlantic continental shelf. Unicellular group A cyanobacteria (UCYN‐A) were most often the dominant diazotrophic group expressing nifH, a gene encoding the nitrogenase enzyme, throughout the study area during all seasons. This expands the domain of these diazotrophs to include coastal waters where dissolved N concentrations are not always depleted. Further, the high rates of N2 fixation and diazotroph diversity along the western North Atlantic continental shelf underscore the need to reexamine the biogeography and the activity of diazotrophs along continental margins. Accounting for this substantial but previously overlooked source of new N to marine systems necessitates revisions to global marine N budgets.Data presented in the body and supporting information of this manuscript have been deposited in the National Aeronautics and Space Administration (NASA) repository, SeaBASS and is publicly available at the following DOI address: 10.5067/SeaBASS/CLIVEC/DATA 001. This work was supported by a grant from NASA Grant Number: NNX09AE45G to M. R. M., A. M., and K. H.; a grant from NSF to P. D. C; and the Jacques S. Zaneveld and Neil and Susan Kelley Endowed Scholarships to C. S. We thank NOAA for ship time and the captain and crew of NOAA vessels Delaware II and Henry Bigelow for assistance during field sampling. Data have been submitted to SeaBASS (https://seabass.gsfc.nasa.gov/), NASA's preferred archival repository

The VEGF receptor Flt-1 spatially modulates Flk-1 signaling and blood vessel branching

Blood vessel formation requires the integrated regulation of endothelial cell proliferation and branching morphogenesis, but how this coordinated regulation is achieved is not well understood. Flt-1 (vascular endothelial growth factor [VEGF] receptor 1) is a high affinity VEGF-A receptor whose loss leads to vessel overgrowth and dysmorphogenesis. We examined the ability of Flt-1 isoform transgenes to rescue the vascular development of embryonic stem cell–derived flt-1−/− mutant vessels. Endothelial proliferation was equivalently rescued by both soluble (sFlt-1) and membrane-tethered (mFlt-1) isoforms, but only sFlt-1 rescued vessel branching. Flk-1 Tyr-1173 phosphorylation was increased in flt-1−/− mutant vessels and partially rescued by the Flt-1 isoform transgenes. sFlt-1–rescued vessels exhibited more heterogeneous levels of pFlk than did mFlt-1–rescued vessels, and reporter gene expression from the flt-1 locus was also heterogeneous in developing vessels. Our data support a model whereby sFlt-1 protein is more efficient than mFlt-1 at amplifying initial expression differences, and these amplified differences set up local discontinuities in VEGF-A ligand availability that are important for proper vessel branching

Defining the Realized Niche of the Two Major Clades of \u3ci\u3eTrichodesmium\u3c/i\u3e: A Study on the West Florida Shelf

The cyanobacterium Trichodesmium plays an essential role supporting ocean productivity by relieving nitrogen limitation via dinitrogen (N-2) fixation. The two common Trichodesmium clades, T. erythraeum and T. thiebautii, are both observed in waters along the West Florida Shelf (WFS). We hypothesized that these taxa occupy distinct realized niches, where T. thiebautii is the more oceanic clade. Samples for DNA and water chemistry analyses were collected on three separate WFS expeditions (2015, 2018, and 2019) spanning multiple seasons; abundances of the single copy housekeeping gene rnpB from both clades were enumerated via quantitative PCR. We conducted a suite of statistical analyses to assess Trichodesmium clade abundances in the context of the physicochemical data. We observed a consistent coastal vs. open ocean separation of the two clades: T. erythraeum was found in shallow waters where the concentrations of dissolved iron (dFe) and the groundwater tracer Ba were significantly higher, while T. thiebautii abundance was positively correlated with water column depth. The Loop Current intrusion in 2015 with entrained Missisippi River water brought higher dFe and elevated abundance of both clades offshore of the 50 m isobath, suggesting that both clades are subject to Fe limitation on the outer shelf. Whereas, previous work has observed that T. thiebautii is more abundant than T. erythraeum in open ocean surface waters, this is the first study to examine Trichodesmium niche differentiation in a coastal environment. Understanding the environmental niches of these two key taxa bears important implications for their contributions to global nitrogen and carbon cycling and their response to global climate change

The VEGF receptor Flt-1 spatially modulates Flk-1 signaling and blood vessel branching

Blood vessel formation requires the integrated regulation of endothelial cell proliferation and branching morphogenesis, but how this coordinated regulation is achieved is not well understood. Flt-1 (vascular endothelial growth factor [VEGF] receptor 1) is a high affinity VEGF-A receptor whose loss leads to vessel overgrowth and dysmorphogenesis. We examined the ability of Flt-1 isoform transgenes to rescue the vascular development of embryonic stem cell–derived flt-1−/− mutant vessels. Endothelial proliferation was equivalently rescued by both soluble (sFlt-1) and membrane-tethered (mFlt-1) isoforms, but only sFlt-1 rescued vessel branching. Flk-1 Tyr-1173 phosphorylation was increased in flt-1−/− mutant vessels and partially rescued by the Flt-1 isoform transgenes. sFlt-1–rescued vessels exhibited more heterogeneous levels of pFlk than did mFlt-1–rescued vessels, and reporter gene expression from the flt-1 locus was also heterogeneous in developing vessels. Our data support a model whereby sFlt-1 protein is more efficient than mFlt-1 at amplifying initial expression differences, and these amplified differences set up local discontinuities in VEGF-A ligand availability that are important for proper vessel branching