Browsing by Subject "Diatoms"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item The effect of crude oil and chemical dispersant on sinking rates of Gulf of Mexico diatoms(2015-12) Oh, Genesok; Villareal, Tracy Alan; Buskey, Edward J; Liu, ZhanfeiIn the open and coastal ocean, primary productivity is derived largely from phytoplankton. Diatoms are a major group of phytoplankton that account for almost half of all oceanic primary production. Sinking is a fundamental aspect of diatom ecology usually linked to loss process but is important in vertical migration for nutrient uptake, avoidance of predators, and completion of lifecycle events. Sinking is tightly linked to both physiological state and size of diatom cells. Oil spills are one of the many stressors now evident in the marine environment. Since diatom physiology is generally adversely affected by crude oil in the form of growth inhibition, reduced photosynthesis, and cell death, it was hypothesized that diatom sinking would be adversely affected by the addition of crude oil, and that increasing concentration, time, and the addition of chemical dispersant would magnify this effect. There has been no previous study attempting to quantify how diatom sinking is affected by the presence of crude oil and chemical dispersant. In this study, laboratory cultures of diatom species were experimentally treated with crude oil, dispersant, and a mixture that was filmed at three timepoints over the course of a week. Images were processed with ImageJ to quantify individual trajectories. There were 20-50 cells examined per treatment, with a goal of 50 observed cells. Killed cells showed higher average sinking rates (C. wailesii=93.7 ± 32.9 m day-1, H. cuneformis= 22.9 ± 5.37 m day-1) than the highest observed treatment (C. wailesii=65.9 ± 26.9 m day-1, H. cuneformis=20 ± 5.66 m day-1). There was no clear trend of increased mean sinking rate with respect to treatment or time. Clear doseresponse curves for sinking were not evident. Skewness and kurtosis was calculated for each treatment to examine changes in the frequency distributions of sinking rate histograms, and compared to the controls to observe any patterns of change in central tendency or kurtosis. There was no trend with respect to skewness or kurtosis, although the data suggests there may be species-specific differences in response in H. cuneformis and Skeletonema spp. treatments, where one side of the skewness axis was favored. The data suggests that exposure to crude oil and chemical dispersant does not elicit a clear increase in sinking rate. If these results can be generalized to the field, then diatom population changes after an oil spill is likely not due to major changes in sinking losses.Item Phylogeny and evolutionary ecology of thalassiosiroid diatoms(2006-08) Alverson, Andrew James; Theriot, Edward C. (Edward Claiborne), 1953-Salinity is a significant barrier to the distribution of diatoms, and though it is generally understood that diatoms are ancestrally marine, the number of times diatoms independently colonized fresh waters and the adaptations that facilitated these colonizations remain outstanding questions in diatom evolution. Resolving the exact number of freshwater colonizations will require large-scale phylogenetic reconstruction with dense sampling of marine and freshwater taxa. A more tractable approach to understanding the marine--freshwater barrier is to study a group of diatoms with high diversity in each habitat. The "centric" diatom order Thalassiosirales affords an excellent opportunity to study the origin and evolution of diatoms in fresh waters. Thalassiosirales is a well-supported monophyletic group common in marine, brackish, and freshwater habitats. Thalassiosirales species historically are classified into the marine Thalassiosiraceae or freshwater Stephanodiscaceae, reflecting the more generally held hypothesis that diatoms are naturally split along marine--freshwater lines. The fossil record suggests that Stephanodiscaceae traces to a single colonization of freshwater in the mid-Miocene, and in addition, Stephanodiscaceae species share a suite of complex cell wall characters, which has been interpreted as corroborating evidence for their monophyly. I reconstructed the phylogeny of Thalassiosirales and used the phylogeny to test these and other hypotheses and to address a number of other problems related to the marine--freshwater boundary in diatoms. Phylogenetic analyses showed strong evidence for multiple colonizations of freshwater and reject all previous colonization hypotheses. Results further show that part of Stephanodiscaceae is an early diverging lineage within Thalassiosirales, indicating that these two distantly related and separately derived Stephanodiscaceae lineages independently evolved a similar set of complex morphological features upon or shortly after the colonization of fresh waters. Finally, marine and freshwater diatoms, including Thalassiosirales, show several important differences in silicon physiology. In addition to containing an order of magnitude more silica in their cell walls, freshwater diatoms have a drastically lower enzymatic affinity for silicic acid, the dissolved form of silica used by diatoms. I sequenced the silicon transporter genes from marine and freshwater Thalassiosirales and show that physiological differences are not due to differences in the coding sequence.Item Rock snot in the age of transcriptomes : using a phylogenetic framework to identify genes involved in diatom extracellular polymeric substance-secretion pathways(2013-12) Ashworth, Matt Peter; Theriot, Edward C. (Edward Claiborne), 1953-; Jansen, Robert K., 1954-We are coming to understand that the ecological importance of diatoms is not limited to primary productivity, as many diatoms produce extracellular polymeric substances (EPS), which are vital components in algal and bacterial “biofilms.” While great effort has been made to chemically identify the types of molecules and polymers used to create and modify diatom EPS there is still much about the process we do not know. Rather than studying this process chemically, we have elected to search for the genes involved in EPS production and secretion. We assembled transcriptomes from three EPS-producing diatoms (Cyclophora tenuis, Lucanicum concatenatum, Thalassionema frauenfeldii) and two diatoms which do not (Astrosyne radiata, Thalassionema sp. ‘BlueH20’). In an attempt to limit the differences to EPS-related transcripts, the taxa were selected in a phylogenetic framework (which is also discussed in this dissertation), where EPS-producing taxa were closely-related to taxa which did not produce EPS (A. radiata, C. tenuis, L. concatenatum as one set, T. frauenfeldii and T. sp. ‘BlueH20’ as the other). The resulting pool of transcripts sorted for contigs which appeared in the EPS-producing taxa but not their closely-related non EPS-producing counterparts, and those contigs were then compared to two annotated diatom genomes and sorted by function, looking specifically for genes related to secretion, polysaccharide assembly or modification and carbohydrate metabolism. In the Thalassionema clade, 41 contigs with the aforementioned annotations were found, while 22 such contigs were found in the Cyclophora/Lucanicum/Astrosyne clade. These putative EPS-related markers are identified in this dissertation for further study on their function and evolution across diatoms.