Department of Biology (Fredericton)

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The utility of growth form for predicting and evaluating aquatic plant nutrient relations
The utility of growth form for predicting and evaluating aquatic plant nutrient relations
by Christopher Dean Tyrrell, My dissertation focuses on the role of agricultural nutrient enrichment in structuring aquatic plant communities in Southern Manitoba, Canada, and changes in nutrient cycling resulting from changes in vegetation structure. Built around the “holy grail” framework of community ecology, which describes connections between the environment and ecosystem services or function as mediated by the traits of the biotic community, I explore the linkages between nutrient enrichment and aquatic plants of prairie streams focusing on species growth form (morphology) as a proxy for a suite of co-varying individual traits. I found that plant morphology interacted with environmental factors to determine which growth forms predominated in a stream: plant community shifts from being dominated by species with a submerged morphology to a community dominated by an emergent morphology as nutrient concentrations increase. I show how this pattern allows plant growth form to be used as an indicator of stream nutrient status. Further, I found that plants with similar growth forms share similar physiological features. Emergent plants have lower tissue nutrient concentrations per unit biomass and thus transfer fewer nutrients per unit biomass from the sediment to the water column than submerged plants. My work also includes a phylogenetic thread that brings novel insight: species at sites with higher nutrients all tend to be clustered in a few branches of the plant phylogeny whereas stream sites with lower nutrients have species from a diverse mixture of phylogenetic lineages. I used plant phylogeny to examine whether evolutionary history is related to tissue nutrient concentration and found the influence is mostly attributable to phenotype. These findings hint at the possibility of alternative stable states for prairie stream vegetation: a high nutrient emergent community and a low nutrient submerged community. These alternative states are comparable to those found in shallow lakes, where high nutrient conditions are dominated by algal growth and bring about turbid water, whereas lower nutrients are characterized by clear water and abundant macrophyte growth. The nutrient transferring functionality of these two vegetation states should also differ, but specific quantities transferred would dependent on the proportion of biomass of each growth form., Electronic Only. (UNB thesis number) Thesis 9589. (OCoLC)959237866., Ph.D. University of New Brunswick, Department of Biology, 2015.
Tissue-specific compensatory mechanisms and erythropoiesis in triploid zebrafish
Tissue-specific compensatory mechanisms and erythropoiesis in triploid zebrafish
by Christopher David Small, In eukaryotes, cell size is proportional to the size of the nucleus and to the amount of genomic DNA housed within. Ploidy transitions, or Whole Genome Duplications (WGDs), double the amount of genomic DNA in the nucleus and cell size is increased consequently. Genome duplication is a driver for the evolution of novel traits by producing genetic redundancy that buffers the negative fitness consequences of mutations in highly conserved genes. WGDs have been discovered in nearly every major taxon of multicellular eukaryotes, but are more common in plants than in animals for reasons that are not clear. In plants, changes in ploidy and genome size changes the size of the organism as the number of cells allocated to tissues does not compensate for larger cells. In contrast, cell size and body size are decoupled in vertebrates so polyploids are no larger than concomitant diploids. Research on the evolution of polyploids usually focuses on the fate of duplicated genes rather than on the developmental and physiological consequences of changing cell size and the cellular granularity of tissues (the degree to which a tissue is subdivided into discrete cells). Perhaps the relative scarcity of WGDs in animals pertains more to how these developmental and physiological consequences affect fitness rather than the evolutionary consequences that occur in later generations after polyploids have successfully reproduced. Ploidy can be experimentally manipulated in most teleosts, but diploid/triploid comparisons are most common as triploids are reproductively sterile making them useful for the aquaculture industry. Triploids consistently underperform compared to diploids with reduced ability to tolerate stressful conditions and higher mortality rates when raised in conditions optimized for diploids. Triploids typically struggle to tolerate aerobic challenges leading many to suggest a cardiorespiratory limitation, but there is no clear mechanism explaining this difference between ploidies. The zebrafish is a popular model vertebrate that has been a boon for developmental biologists and, increasingly, physiologists. In this thesis, I have taken advantage of the many mutants and transgenic strains with tissue-specific fluorescent reporters to answer questions about the biology of polyploid vertebrates that would not be possible in classic, non-model species such as in Atlantic salmon. To do so, I developed a novel ploidy determination technique to non-lethally assess the amount of DNA in the nuclei of zebrafish embryos in vivo using confocal microscopy and image processing (Chapter 2). I demonstrated for the first time that the compensatory mechanisms maintaining organ and body size in polyploids are tissue-specific by comparing the morphology of the blood, muscle, and the vasculature at single cell resolution (Chapter 3). Focusing in on the blood and erythropoietic system, I quantified hematopoietic stem cells in diploid and triploid embryos to show that triploids have fewer of these blood progenitor cells in their hematopoietic tissue. Triploids also produce erythrocytes at a slower rate compared to diploids suggesting that there are more aged, senescent erythrocytes in circulation perhaps contributing to the well-documented physiological limitations of triploids compared to diploids (Chapter 4). The utility of the zebrafish system makes it an ideal organism for studying the biology of polyploids not only to improve the performance of triploids in aquaculture, but also to better understand why polyploidy is rarer in animals than in plants., Electronic Only.
Transcriptomic and photophysiological responses to light stress in Bigelowiella natans
Transcriptomic and photophysiological responses to light stress in Bigelowiella natans
Chlorarachniophytes, a group of marine unicellular amoeboflagellates, have acquired their plastid secondarily from a green alga transferring photosynthesis into the heterotrophic Rhizarian host. The evolutionary integration of organisms over time must coordinate gene expression to regulate stress responses. However, the light response mechanism has not been studied in chlorarachniophytes. I conducted an RNA-seq experiment to identify transcriptome changes under high (HL) or very-low (VL) light stress, in the model chlorarachniophyte, Bigelowiella natans. Under HL, genes involved in primary metabolism and detoxification increased, while VL reduced expression of genes in carbon metabolism and photosynthesis. The light-harvesting complex (LHC) genes with diverse origins from green and red algae were highly responsive to light stress. Two classes of LHCs were over-expressed only in HL, suggesting a role in photoprotective mechanisms like non-photochemical quenching. Together, B. natans displays distinct acclimation strategies that incorporated endosymbiont and host regulatory frameworks to cope with light stress.
Turnover rates and trophic discrimination factors of δ34s in brook trout, Salvelinus fontinalis
Turnover rates and trophic discrimination factors of δ34s in brook trout, Salvelinus fontinalis
by Michelle Andrea Charest, Stable isotope analysis (SIA) of sulphur, like carbon and nitrogen SIA, can be applied to understand food webs, animal movements, and nutrient dynamics. Sulphur SIA is of particular interest for movement studies of anadromous fishes because of the large variation between freshwater and marine sulphur (δ34S) stable isotope values. The application of this tool is dependent on our knowledge of the isotopic change between a consumer and its diet or the trophic discrimination factor (Δδ34S), and the turnover rate of the element in the organism’s tissues. The objectives of this study were to determine the Δδ34S and turnover rate of sulphur in liver, muscle, blood and caudal fin tissues, of brook trout (Salvelinus fontinalis), using laboratory and field experiments. At the start of the laboratory experiment, brook trout were fed a diet with a δ34S value of 5.8±0.3‰, relative to their previous diet that had a δ34S value of 15.9±0.2‰. For the field experiment, hatchery-reared brook trout were introduced to a New Brunswick stream, where their sulphur turnover rate and Δδ34S were monitored in situ. These trout had an initial δ34S value that was high relative to their natural diet in the stream. Subsequent sampling over several months permitted a comparison of natural and laboratory-derived turnover rates of sulphur in their tissues. The turnover rates from the laboratory results indicated the sulphur turnover was most rapid in liver and caudal fin and was slowest in blood and muscle. Similar turnover results were found in the field experiment. Laboratory measured Δδ34S of those tissues that reached steady state averaged ~1‰ and the average Δδ34S for all the tissues sampled from the Otter Brook resident brook trout in the field experiment was ~ 0 ‰. Results of this study will facilitate the use of sulphur as a third isotopic tracer in food web studies, and to successfully track fish movements.
Turnover time and annual migration of Clupea harengus Atlantic herring on the German Bank and Scot's Bay spawning grounds :
Turnover time and annual migration of Clupea harengus Atlantic herring on the German Bank and Scot's Bay spawning grounds :
by Jeffrey Ryan Martin, This study examined eleven years of mark and recapture data to quantify turnover time, defined as the time required for individuals to aggregate, spawn and exit the spawning area, of Clupea harengus Atlantic herring on the German Bank and Scot's Bay spawning grounds off eastern Canada. Herring migrating from the Scot's Bay spawning ground have a shorter mean turnover time and faster dispersal rate than German Bank herring. Most post-spawned Scot's Bay herring migrated to the approaches of the Bay of Fundy where they mixed with German Bank herring. German Bank herring were more broadly distributed, occurring near the approaches of the Bay of Fundy, throughout the Gulf of Maine, and on Scotian Shelf. No mixing of the two populations occurred during spawning indicating self-sustaining reproductively isolated populations. The two populations only mixed during feeding and overwintering. Population specific turnover times calculated in this study improve current methods of estimating spawning stock biomass, thereby reducing the risk of overexploiting the resource., Electronic Only., M.Sc. University of New Brunswick, Department of Biology, 2014.
Using traits-based ecology to inform aquatic insect assemblage structure in relation to environmental flows
Using traits-based ecology to inform aquatic insect assemblage structure in relation to environmental flows
by Jessica M. Orlofske, Benthic macroinvertebrate taxonomic data is the foundation of freshwater biomonitoring programs.around the world. Biological trait information has been proposed as an effective alternative or supplement to taxonomic data for ·biomonitoring purposes. Traits are simply measurable, heritable properties of an organism that interact with the environment. Trait data can expand the geographical scope of assessments as well as describe mechanistic relationships between environmental conditions and the biological community to diagnose impact severity and type of stressor. In riverine ecosystems, a change in the flow regime or hydrological alteration is considered the most significant environmental stressor because of the detrimental effects on biological communities and habitats as well as interactions with other stressors. To maintain ecological integrity, trait data can inform the benthic macroinvertebrate assemblage response to flow properties to support environmental flow management criteria. My objective was to define and evaluate traits and trait metrics that could be linked to hydrological conditions. Specifically, I investigated intra- and inter-tax on trait properties for body size and body shape, which are predicted to respond strongly to hydraulic and hydrologic scale variables. Multiple field sites were sampled several times over a five-year period in the unregulated Miramichi River Basin, New Brunswick, Canada to resolve the relationships between flow and ecology. I was able to demonstrate the importance of intraspecific trait variation and trait properties for characterizing the benthic assemblage. By measuring specimen body sizes and establishing body shape criteria using geometric morphometric analysis, I improved the accuracy of traits-based metrics and demonstrated a sizedependent bias in current taxonomic-based metrics. Using both traditional categorical trait states as well as high-resolution trait data, I was able to characterize relationships among aquatic insects and hydrological properties at nested spatial scales. Then I tested the performance of taxonomic and trait metrics to assess hydrological data over short (two-year) to moderate (five-year) temporal scales. High-resolution trait metrics demonstrated equal or greater association with hydrological factors than taxonomic or other trait metrics at these timescales. Trait information can add value to biomonitoring approaches by accurately describing trait expression, enabling stronger statistical inference, and increasing sensitivity and interpretability, which are essential for evaluating the complex relationship between benthic assemblages and their hydrological environment.
Virus induced cell death, evasion and resistance in the harmful bloom-forming alga, Heterosigma akashiwo
Virus induced cell death, evasion and resistance in the harmful bloom-forming alga, Heterosigma akashiwo
by Jennifer E. Dingman, Phytoplankton make up a minute proportion of the Earth’s total biomass yet they contribute almost half of global primary productivity, the discrepancy being a result of the rapid turnover of phytoplankton due to grazing and environmentally-induced mortality. Marine viruses also contribute to this high mortality and often outnumber their hosts by at least an order of magnitude. With an estimated 1023 infections per second, viruses can be responsible for the death of 20% of the ocean’s biomass per day. The magnitude of the threat implies that phytoplankton employ strategies to avoid and limit the extent of viral lysis. However, for most phytoplankton groups, there is little knowledge regarding specific defensive strategies. This thesis investigated specific responses activated in the bloom-forming alga Heterosigma akashiwo in response to heat-stress and three viruses (HaV, HaNIV and HaRNAV) and provides evidence that this alga is capable of an active form of cell death known as programmed cell death (PCD). This cell death has classic hallmarks consistent with apoptosis-like cell death in response to heat-stress, HaV and HaNIV infection, and paraptosis during HaRNAV infection. In addition to PCD, Heterosigma is capable of forming resting cells in response to high-heat (40 and 50°C) and to viral infection with HaV, a DNA virus (Phycodnaviridae), which represents a successful but short-term evasion mechanism against cell death in this alga. The various responses, multiple PCD programs and the formation of resting cells, represent cell and population level survival strategies under stress conditions. The resting-cell phase of Heterosigma's life cycle is essential for population survival during viral infection, in addition to the previously reported overwintering survival strategies. This avoidance strategy would contribute to bloom termination by allowing a proportion of the cells to settle out on the ocean floor and would presumably contribute to a “seed stock” for future blooms when the viral load has decreased. Understanding the triggers and mechanisms underlying the virus induced resting-cell formation could also lead to an approach for the control of toxic algae, like Heterosigma, that are known to kill fish and harm coastal environments.

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