Global climate change is threatening both our water quality and quantity. Specifically, the influence of climate change on freshwater lakes includes decreased water availability, increased evapotranspiration, changes in nutrient availability, and shifts in species composition. Understanding the changes that are occurring to our freshwater ecosystems is imperative to understanding the full impact of climate change on both the environment and society. This thesis examines a shift in sedimentary diatom assemblages towards increased relative abundances of Discostella species, a phenomenon that has been documented across the Northern Hemisphere. One of the central tenants of this work is that it has been done at the Experimental Lakes Area (ELA) in the boreal region of Canada, a study site that is uniquely devoid of large-scale anthropogenic disturbances. An analysis of the long-term monitoring records at the ELA show that Discostella species are primarily spring bloomers, and recent increases in their abundance is linked to changes in spring thermal conditions. To link the changes recorded in the sedimentary records of eight lakes to climate change, and assess whether Discostella species are in fact showing a response to climate change, a novel approach utilizing the theory of temporal synchrony was applied to eight paleo records. Discostella stelligera was found to be synchronous in all eight lakes studied, suggesting that a broad-scale forcing factor is influencing its abundance. Further, it was significantly correlated with annual and winter temperatures, supporting a link to changes in spring thermal conditions as a possible explanation. To assess the relative sensitivity of the study lakes, particularly in comparison to other boreal and temperate region lakes, an analysis was conducted of the timing of the first change in Discostella species. Several statistical techniques were employed and all approaches showed that the study lakes from ELA responded earlier in comparison to other lakes studied from other boreal and temperate regions (ca. 1900 vs ca. 1970), but later than Arctic and Sub-Arctic lakes. We suggest that this may be due to the lack of local disturbances at the ELA and/or the comparably small size of our study lakes. / Thesis (Ph.D, Biology) -- Queen's University, 2014-06-30 15:03:04.447

This thesis was focused on studying diatoms (Bacillariophyceae) from Acadia National Park, Maine, USA. First, the park is introduced and the preliminary study of freshwater algae, including diatoms, is presented. Extraordinary species richness of algae was discovered, especially in the group of diatoms, which is documented by a complete list of 674 diatom taxa in 92 genera encountered in the freshwater and brackish habitats within the park. Of those a considerable number of species unfortunately remained unidentified, as they did not conform to any described taxon in the available scientific literature. Therefore, several of those unnamed taxa were studied in close detail using light and scanning electron microscopes, exhaustive literature and herbaria search, and yielded description of three new species from genus Eunotia, and rediscovery of two rare and almost forgotten Surirella species.

Sequenced diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum belong to the chromist algae harboring secondary plastids, which display distinct evolutionary history when compared to photosynthetic organelles from rhodophytes, green algae and plants. Via secondary endosymbiosis, heterotrophic eukaryotic ancestor of diatoms engulfed red alga, and in addition to the new organelle, it obtained fitness increasing peculiarities in the chimerical cell metabolism and lifestyle. We examined phylogeny and in silico localization of the nuclear-encoded but plastid located enzymes of tryptophan biosynthesis. We suggest that the diatom tryptophan pathway represents an extreme in the trend of plastid (cyanobacterial) enzymes to be replaced by eukaryotic isoforms. In addition, the gene napped during the endosymbiotic gene transfer from the diatom plastid genome to the diatom nucleus (psb28) was described.

Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2016-09-15T13:15:36Z No. of bitstreams: 2 Dissertação - Alline Alves França - 2016.pdf: 2005555 bytes, checksum: 84feb7f2b775249a2495d3a742b1ec05 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-09-15T14:42:25Z (GMT) No. of bitstreams: 2 Dissertação - Alline Alves França - 2016.pdf: 2005555 bytes, checksum: 84feb7f2b775249a2495d3a742b1ec05 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-09-15T14:42:25Z (GMT). No. of bitstreams: 2 Dissertação - Alline Alves França - 2016.pdf: 2005555 bytes, checksum: 84feb7f2b775249a2495d3a742b1ec05 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-03-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / (Pinnularia Ehrenberg (Bacillariophyta) of pristine streams of Central Brazil). This study aimed to inventory the species of the genus Pinnularia present in pristine streams located in the cerrado biome (Midwest Brazil) between the years 2012 and 2013. The periphyton was collected in five streams in the savannah, in different substrates and seasons. Were identified 23 species, of which 17 are on the 1st occurrence of citations for the Midwest Region: P. angustivalva, P. butantanum, P. castraregina, P. divergens var. biconstricta, P. divergens var. mesoleptiformis, P. divergens var. protracta, P. gibba var. subundulata, P. meridiana var. meridiana, P. microstrauron var. rostrata, P. paulensis, P. persudetica var. persudetica, P. subgibba var. angustarea, P. subgibba var. capitada, P. superpaulensis, P. viridiformis var. minor and P. undula var. undula. Taxa that had a higher frequency of occurrence in the studied streams were P. subanglica, P. angustivalva, P. brauniana and P. butantanum. / (Pinnularia Ehrenberg (Bacillariophyta) de córregos prístinos do Brasil Central). Este estudo objetivou inventariar as espécies do gênero Pinnularia presentes em córregos prístinos localizados no bioma cerrado (Centro-Oeste do Brasil) entre os anos de 2012 e 2013. O perifíton foi coletado em cinco córregos no cerrado, em diferentes substratos e períodos sazonais. Foram identificadas 23 espécies, sendo que 17 são primeiras citações de ocorrência para a Região Centro-Oeste: P. angustivalva, P. butantanum, P. castraregina, P. divergens var. biconstricta,P. divergens var. mesoleptiformis, P. divergens var. protracta, P. gibba var. subundulata, P. meridiana var. meridiana, P. microstrauron var. rostrata, P. paulensis, P. persudetica var. persudetica, P. subgibba var. angustarea, P. subgibba var. capitada, P. superpaulensis, P. viridiformis var. minor e P. undula var. undula. Os táxons que tiveram maior freqüência de ocorrência nos córregos analisados foram P. subanglica, P. angustivalva, P. brauniana e P. butantanum.

The goal of this study was to assess the epiphytic diatom community structure of two host species along a karst gradient in the upper Green River, Kentucky to a gain a better understanding of the role of diatoms in the food web. The host species studied were Podostemum ceratophyllum and Cladophora. Percent cover of P. ceratophyllum and Cladophora were quantified in the four study reaches. The host species were sampled near-shore and mid-channel in each reach in September and October of 2013. After diatoms were extracted from the host and enumerated the density and diversity were quantified. Twelve genera were identified with > 91% of the community in each reach being Cocconeis. The second most abundant genus was Achnanthes or Navicula depending on the reach. The density and diversity of diatoms increased longitudinally going downstream. Exceptions to this trend occurred when high flow events disturbed the community. Within reaches there were no differences in diatom diversity in near-shore and mid-channel habitats. Diatom density in near-shore and mid-channel habitats was only different in the most downstream reach. Cladophora had a community twice as dense as P. ceratophyllum, but less diverse. The results of this study indicate that there are longitudinal differences in diatom communities in the upper Green River and host species are an important factor in determining the community composition. The importance of epiphytic diatoms in the food web, however, remains unclear.

L’océan domine la surface de notre planète et joue un rôle majeur dans la régulation de notre biosphère. Par exemple, les microorganismes photosynthétiques vivant dans l’océan produisent 50% de l’oxygène que nous respirons tous les ans, et une grande partie de notre alimentation et des ressources minérales en proviennent. En cette époque de crise écologique liée à l’accumulation anthropogénique de gaz à effet de serre dans l’atmosphère, il est impératif de développer des énergies plus durables que les carburants fossiles. Le biodiesel pourrait être une source de carburant viable et durable pour remplacer le pétrodiesel mais jusque-là, nos efforts visant à produire des lipides à base de microalgues se sont essentiellement concentrés sur des algues vertes. Dans cette thèse je propose des méthodes pour mieux caractériser une autre catégorie de microalgue : les diatomées. Les diatomées sont une composante importante du phytoplancton et contribuent 40% de la production marine de biomasse primaire. Les diatomées accumulent des lipides en réponse à la carence en nutriments, et même si elles semblent accumuler tout autant de lipides que les microalgues vertes, les voies métaboliques menant à l’accumulation de lipides sont encore peu connues.Dans cette thèse je décris notre caractérisation du glycerolipidome de la diatomée modèle Phaeodactylum tricornutum ainsi que notre étude du remodelage de lipides suite à la carence d’azote ou de phosphate. Des accessions de P. tricornutum isolées dans différentes régions de l’océan ont aussi été étudiées afin de comparer leurs réponses au stress nutritif. Nous avons trouvé que la réponse métabolique menant à l’accumulation de lipides en carence d’azote ou de phosphate est différente. En effet, la carence en azote semble déclencher le recyclage des galactoglycerolipides chloroplastiques ainsi qu’une augmentation de la biosynthèse de novo d’acides gras, alors que la carence en phosphate est plus sévère car nous avons observé une accumulation plus significative de triacylglycerols ainsi que la déplétion totale des phospholipides. De plus, nous avons observé des réponses au stress différentes entre les accessions de P. tricornutum, et en particulier concernant leur capacité à accumuler des lipides. Nous proposons l’hypothèse que ces différences sont liées à leur aptitude à recycler du carbone issu de molécules de stockage non lipidiques.Des approches génomiques ont permis de nombreuses avancées pour mieux comprendre le métabolisme des lipides de microalgues mais notre compréhension des voies de biosynthèse de lipides chez les diatomées est encore limitée. Il y a eu diverses tentatives de caractérisation de la réponse au stress de carence par approche transcriptomique mais l’étude de ces données est incomplète du fait de l’annotation insuffisante des gènes encodant les voies métaboliques pertinentes. Ainsi, dans cette thèse je décris nos tentatives d’annotation de gènes impliqués dans le métabolisme des lipides de P. tricornutum ainsi que les approches d’ingénierie génétique visant à mieux caractériser certains de ces gènes. J’ai également utilisé notre nouvelle annotation de gènes impliqués dans le métabolisme des lipides pour effectuer une étude comparative de plusieurs transcriptomes de P. tricornutum en conditions de carence trouvés dans la littérature. J’ai ainsi pu produire une liste de gènes potentiellement impliqués dans l’accumulation de lipides. Enfin, nous avons pu utiliser ces données pour aider l’interprétation de données génomiques et transcriptomiques issues de la diatomée oléagineuse Fistulifera solaris afin de mieux comprendre comment elle accumule des quantités importantes de lipides pour des applications dans le secteur des biotechnologies et des bioénergies. / The ocean dominates the surface of our planet and plays a major role in regulating the biosphere. For example, the microscopic photosynthetic organisms living in the ocean provide 50% of the oxygen we breathe every year, and much of our food and mineral resources are extracted from the ocean. In a time of ecological crisis linked to the accumulation of anthropogenic greenhouse gases in the atmosphere, we must investigate more sustainable energies than fossil fuels. Much attention has been given to biodiesel but so far most efforts to efficiently produce triacylglycerols in microalgae have focused on green algae. In this thesis I propose approaches to better understand another type of microalgae that is significantly divergent from green lineages: diatoms. Diatoms are a major phylum of phytoplankton in the ocean and account for 40% of marine primary productivity. While diatoms appear to be at least as effective as green algae for producing lipids, the fatty acid and glycerolipid biosynthetic pathways leading to their production have not yet been well characterized. Therefore, I propose to better characterize these pathways in the model diatom Phaeodactylum tricornutum in order to help unlock the potential of diatoms for lipid-based biotechnological applications.In this thesis, I discuss our attempts to establish a reference for the glycerolipidome of P. tricornutum and of our assessment of the lipid remodeling and accumulation that occurs in response to nitrogen- and phosphorus-starvation. A range of accessions of P. tricornutum isolated from different parts of the ocean were also examined to compare their responses to nutrient deprivation. We found that the metabolic response leading to lipid accumulation in different nutrient-deprived conditions are distinct. Nitrogen-deprivation appears to trigger the recycling of chloroplastic galactoglycerolipids as well as a strong increase in de novo fatty acid synthesis while the response to phosphorus-deprivation was more severe as we observed a higher triacylglycerol pool and the complete depletion of phospholipids. Furthermore, we observed several differences among accessions of P. tricornutum regarding their ability to accumulate triacylglycerol in response to nutrient starvation and propose the hypothesis that these differences are linked to their ability to recycle intracellular carbon from non-lipid storage molecules.Genome-enabled approaches have also allowed significant steps towards elucidating the lipid metabolism of microalgae in the past decade, but our understanding of diatom metabolic pathways is still limited compared to that of other microalgae and higher plants. There have been several attempts to characterize the stress response in P. tricornutum by using transcriptomic approaches but this data is difficult to exploit to its full potential without a better annotation of genes encoding the relevant pathways. Therefore, in this thesis I discuss our attempts to annotate P. tricornutum lipid metabolism genes. Based on this annotation I have attempted to better characterize a selection of genes by genetic engineering and have pursued a comparative study of several published transcriptomes of P. tricornutum in nutrient deprived conditions to produce a list of candidate genes likely to be involved in triacylglycerol accumulation. Finally, we used this data to help interpret genome and transcriptome data of the newly sequenced oleaginous diatom Fistulifera solaris to help understand how it accumulates unusually high amounts of triacylglycerol for applications in the biotechnology and bioenergy industry.

No description available.

Recent use of molecular methods to revisit taxonomically problematic diatom species revealed severe limitations of morphological species concept. Characterization of diatom species which was based solely on the morphology of their frustules often generated too broad species boundaries which inevitably lead to wrong conclusions about their ecology and distribution. Widespread opinion that many diatom species are cosmopolitan generalists resulted in a theory that dispersal of diatoms is not limited by geographical distance. However, a number of recent studies showed that dispersal of diatoms is governed by the same rules which matter for macroorganisms. Proposed master thesis addresses the topic of diversity and dispersal in diatom species complex Frustulia rhomboides sensu lato in Europe and New Zealand. Results suggest that: (1) although revealed molecular variability in this complex shows clear ecological and biogeographical signal, it is not correlated in morphology. This is another support to general need for adoption of different species concept in diatoms. (2) A considerably uneven ratio in species diversity of genus Frustulia found in ecological similar habitats in Europe and New Zealand supports the idea that diatom dispersal is limited and stressed the need for studies dealing with biogeography.

Seasonal sea ice is an important component of the global climate system. Sea ice influences exchange rates of heat, moisture, and gas between the ocean and atmosphere. Sea ice also plays critical roles in high latitude ecosystems and marine carbon cycling. Records of sea-ice extent and duration in the Arctic Ocean and its marginal seas through geologic time are valuable resources for better understanding the intricate relationships between sea ice and climate. IP25, a compound biosynthesized exclusively by diatoms associated with sea ice, has been used to construct qualitative records of sea ice from sediment cores in some areas of the Arctic. However, IP25 has not previously been applied to sediments from the Bering and Chukchi Seas. This area exhibits a wide range of interannual seasonal ice duration, which makes the region a promising natural laboratory for developing a quantitative core-top calibration between sea ice and the IP25 biomarker. A sample suite of surface sediments from the Bering and Chukchi Seas representing a range of latitudes (60-72o N) and durations of sea ice per year (0.5-11 months/year) are analyzed for this study. Gas chromatography/mass spectrometry analysis of sediment solvent extracts reveals the presence of IP25 in all samples and higher IP25 concentrations in the Chukchi Sea compared to in the Bering Sea. IP25 concentrations are compared with data for several sea surface conditions: mean annual sea-ice duration, sea surface temperature and salinity, and insolation data. An exponential relationship between TOC-normalized IP25 concentration and average annual duration of sea ice is identified. Negative exponential relationships are identified between IP25 and the other sea surface conditions: average annual and August sea surface temperature and average annual and August sea surface salinity. Exponential relationships are also identified between TOC-normalized IP25 concentrations and insolation, and insolation coupled with sea-ice concentration. IP25 in surface sediments is a viable quantitative proxy for sea-ice duration in the Bering and Chukchi Seas. However, sea surface conditions, such as temperature, salinity, sea-ice duration/concentration, and insolation are not independent variables. Therefore it is difficult to determine which of these environmental factors has/have the most influence on IP25 production. Further research and statistical analysis may serve to refine these relationships.

No description available.