Browsing by Author "Hoadley, Kenneth D."
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Item Distribution of CpG Motifs in Upstream Gene Domains in a Reef Coral and Sea Anemone: Implications for Epigenetics in Cnidarians(Public Library of Science (PLOS), 2016-03-07) Marsh, Adam G.; Hoadley, Kenneth D.; Warner, Mark E.; Adam G. Marsh, Kenneth D. Hoadley, Mark E. Warner; Marsh, Adam G.; Hoadley, Kenneth D.; Warner, Mark E.Coral reefs are under assault from stressors including global warming, ocean acidification, and urbanization. Knowing how these factors impact the future fate of reefs requires delineating stress responses across ecological, organismal and cellular scales. Recent advances in coral reef biology have integrated molecular processes with ecological fitness and have identified putative suites of temperature acclimation genes in a Scleractinian coral Acropora hyacinthus.We wondered what unique characteristics of these genes determined their coordinate expression in response to temperature acclimation, and whether or not other corals and cnidarians would likewise possess these features. Here, we focus on cytosine methylation as an epigenetic DNA modification that is responsive to environmental stressors. We identify common conserved patterns of cytosine-guanosine dinucleotide (CpG) motif frequencies in upstream promoter domains of different functional gene groups in two cnidarian genomes: a coral (Acropora digitifera) and an anemone (Nematostella vectensis). Our analyses show that CpG motif frequencies are prominent in the promoter domains of functional genes associated with environmental adaptation, particularly those identified in A. hyacinthus. Densities of CpG sites in upstream promoter domains near the transcriptional start site (TSS) are 1.38x higher than genomic background levels upstream of -2000 bp from the TSS. The increase in CpG usage suggests selection to allow for DNA methylation events to occur more frequently within 1 kb of the TSS. In addition, observed shifts in CpG densities among functional groups of genes suggests a potential role for epigenetic DNA methylation within promoter domains to impact functional gene expression responses in A. digitifera and N. vectensis. Identifying promoter epigenetic sequence motifs among genes within specific functional groups establishes an approach to describe integrated cellular responses to environmental stress in reef corals and potential roles of epigenetics on survival and fitness in the face of global climate change.Item Investigating physiological variability across different algal and cnidarian symbioses:possible implications for climate change(University of Delaware, 2016) Hoadley, Kenneth D.The unique and mutualistic symbioses between scleractinian corals and the dinoflagellate algae Symbiodinium spp. is critical to the overall success and continual growth of many reef corals worldwide. Unfortunately, these symbioses are susceptible to rising oceanic temperature and changes in carbonate chemistry. However, high genetic diversity within the host and symbiont suggests their responses may vary in a species-specific manner, potentially forming coral climate change ‘winners’ and ‘losers’. Here I initially identified potential interactive effects between elevated temperature and pCO2 concentration on the biochemical composition (protein, carbohydrate and lipid content) of the host and symbiont portions within four Pacific coral species and their respective symbionts. Temperature was the principle driver of physiological change and each host + symbiont combination responded to the stress differently, as greater change in biochemical composition was noted within the more thermally tolerant symbioses (M. monastrea and T. reniformis). I extended the question of interactive effects between independent variables by including nutrient concentration as a factor, along with temperature and pCO 2, focusing only on the coral T. reniformis with its symbiont S. trenchii. Temperature remained the leading factor in driving physiological change as net photosynthesis and cellular chlorophyll a increased with temperature under ambient pCO2, whereas temperature related differences in cellular volume were more pronounced under elevated pCO2. Additionally, increased nutrient concentrations mitigated thermal affects under all pCO 2 conditions and suggest significant interactive effects between temperature, pCO2 and nutrient concentrations. Given the variability in physiological response to both temperature and pCO2 previously observed, I next focused on a better characterization of the unique symbioses established within each host and symbiont combination, including two non-calcifying and symbiotic species. Specifically, I utilized multiple cnidarian symbioses to ask if symbiont type affects translocation of energy rich photosynthate to the host and if this varies with changes in pCO2 and temperature. Two calcifying scleractinian corals (Montipora hirsuta and Pocillopora damicornis) and one non-calcifying coral (Discosoma nummiforme) were exposed to the individual and combined effects of elevated temperature and pCO2 in order to induce a range of physiological states within each symbioses. An inverse relationship between cellular density and net photosynthesis is observed, as were differences in the ratio of photosynthesis cell-1 to carbon translocation cell-1, which appeared to be dependent on the host+symbiont combination. Because anemones represent one of the few cnidarian species where positive effects of elevated pCO2 have been consistently documented, I also measured carbon uptake and translocation along with asexual reproduction within the anemone Exaiptasia pallida under ambient and elevated pCO2 conditions. Additionally we asked whether physiological differences could be detected at the symbiont sub species level, by infecting the host anemones with different S. minutum genotypes. Elevated pCO2 conditions did increase net photosynthesis, carbon incorporation and asexual budding. Subtle differences were also observed across host/symbiont genotypes, placing functional significance on genotypic variance below the species level. I also had the opportunity to extend our comparison of host + symbiont diversity through field studies conducted in Palau. There I investigated the diversity of response strategies to elevated temperature for six congeneric coral species collected from an inshore rock island habitat and an offshore reef-system. Inshore reef corals harbored different symbiont species than their offshore counterparts and likely played a major role in establishing the greater thermal tolerance observed for colonies collected from the warmer inshore reefs. Host dependent differences in symbiont physiology were also observed and affected the overall response to high temperature. Although symbiont phenotype can certainly provide a major source of adaptive potential for corals as they combat future climate change scenarios, host physiology also remains an important factor in establishing thermal resistance. As a proxy for phenotypic plasticity within the host coral, I quantified epigenetic modification of cytosine residues within the E. pallida genome in response to elevated temperature and across anemones housing B1 vs. D4-5 symbionts. Clear structure in CpG density across functional gene categories was apparent in both the promoter and gene body regions for E. pallida and changes in methylation status occurred in response to both temperature and symbiont species. Interestingly, the average net increase in methylation status observed between low and high temperature and between B1 and D4-5 symbionts are significantly higher within the promoter region as compared to gene introns and exons and may point to the promoter regions as an important target for epigenetic control through DNA methylation.Item Partitioning of Respiration in an Animal-Algal Symbiosis: Implications for Different Aerobic Capacity between Symbiodinium spp.(Frontiers Media S.A., 2016-04-18) Hawkins, Thomas D.; Hagemeyer, Julia C. G.; Hoadley, Kenneth D.; Marsh, Adam G.; Warner, Mark E.; Thomas D. Hawkins, Julia C. G. Hagemeyer, Kenneth D. Hoadley, Adam G. Marsh and Mark E. Warner; Hawkins, Thomas D.; Hagemeyer, Julia C. G.; Hoadley, Kenneth D.; Marsh, Adam G.; Warner, Mark ECnidarian-dinoflagellate symbioses are ecologically important and the subject of much investigation. However, our understanding of critical aspects of symbiosis physiology, such as the partitioning of total respiration between the host and symbiont, remains incomplete. Specifically, we know little about how the relationship between host and symbiont respiration varies between different holobionts (host-symbiont combinations). We applied molecular and biochemical techniques to investigate aerobic respiratory capacity in naturally symbiotic Exaiptasia pallida sea anemones, alongside animals infected with either homologous ITS2-type A4 Symbiodinium or a heterologous isolate of Symbiodinium minutum (ITS2-type B1). In naturally symbiotic anemones, host, symbiont, and total holobiont mitochondrial citrate synthase (CS) enzyme activity, but not host mitochondrial copy number, were reliable predictors of holobiont respiration. There was a positive association between symbiont density and host CS specific activity (mg protein−1), and a negative correlation between host- and symbiont CS specific activities. Notably, partitioning of total CS activity between host and symbiont in this natural E. pallida population was significantly different to the host/symbiont biomass ratio. In re-infected anemones, we found significant between-holobiont differences in the CS specific activity of the algal symbionts. Furthermore, the relationship between the partitioning of total CS activity and the host/symbiont biomass ratio differed between holobionts. These data have broad implications for our understanding of cnidarian-algal symbiosis. Specifically, the long-held assumption of equivalency between symbiont/host biomass and respiration ratios can result in significant overestimation of symbiont respiration and potentially erroneous conclusions regarding the percentage of carbon translocated to the host. The interspecific variability in symbiont aerobic capacity provides further evidence for distinct physiological differences that should be accounted for when studying diverse host-symbiont combinations.Item Thermotolerant coral–algal mutualisms maintain high rates of nutrient transfer while exposed to heat stress(Proceedings of the Royal Society B: Biological Sciences, 2023-09-20) Kemp, Dustin W.; Hoadley, Kenneth D.; Lewis, Allison M.; Wham, Drew C.; Smith, Robin T.; Warner, Mark E.; LaJeunesse, Todd C.Symbiotic mutualisms are essential to ecosystems and numerous species across the tree of life. For reef-building corals, the benefits of their association with endosymbiotic dinoflagellates differ within and across taxa, and nutrient exchange between these partners is influenced by environmental conditions. Furthermore, it is widely assumed that corals associated with symbionts in the genus Durusdinium tolerate high thermal stress at the expense of lower nutrient exchange to support coral growth. We traced both inorganic carbon (H13CO3–) and nitrate (15NO3–) uptake by divergent symbiont species and quantified nutrient transfer to the host coral under normal temperatures as well as in colonies exposed to high thermal stress. Colonies representative of diverse coral taxa associated with Durusdinium trenchii or Cladocopium spp. exhibited similar nutrient exchange under ambient conditions. By contrast, heat-exposed colonies with D. trenchii experienced less physiological stress than conspecifics with Cladocopium spp. while high carbon assimilation and nutrient transfer to the host was maintained. This discovery differs from the prevailing notion that these mutualisms inevitably suffer trade-offs in physiological performance. These findings emphasize that many host–symbiont combinations adapted to high-temperature equatorial environments are high-functioning mutualisms; and why their increased prevalence is likely to be important to the future productivity and stability of coral reef ecosystems.