Browsing by Author "von Dassow, Peter"

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    Abundances and morphotypes of the coccolithophore Emiliania huxleyi in southern Patagonia compared to neighbouring oceans and Northern Hemisphere fjords
    (COPERNICUS GESELLSCHAFT MBH, 2021) Diaz Rosas, Francisco; Alves de Souza, Catharina; Alarcon, Emilio; Menschel, Eduardo; Gonzalez, Humberto E.; Torres, Rodrigo; von Dassow, Peter
    Coccolithophores are potentially affected by ongoing ocean acidification, where rising CO2 lowers seawater pH and calcite saturation state (omega(cal)). Southern Patagonian fjords and channels provide natural laboratories for studying these issues due to high variability in physical and chemical conditions. We surveyed coccolithophore assemblages in Patagonian fjords during late spring 2015 and early spring 2017. Surface omega(cal) exhibited large variations driven mostly by freshwater inputs. High-omega cal conditions (max. 3.6) occurred in the Archipelago Madre de Dios. omega(cal) ranged from 2.0-2.6 in the western Strait of Magellan and 1.5-2.2 in the inner channel and was subsaturating (0.5) in Skyring Sound. Emiliania huxleyi was the only coccolithophore widely distributed in Patagonian fjords (> 96 % of total coccolithophores), only disappearing in the Skyring Sound, a semi-closed mesohaline system. Correspondence analysis associated higher E. huxleyi biomasses with lower diatom biomasses. The highest E. huxleyi abundances in Patagonia were in the lower range of those reported in Norwegian fjords. Predominant morphotypes were distinct from those previously documented in nearby oceans but similar to those of Norwegian fjords. Moderately calcified forms of E. huxleyi A morphotype were uniformly distributed throughout Patagonia fjords. The exceptional R/hyper-calcified coccoliths, associated with low omega(cal) values in Chilean and Peruvian coastal upwellings, were a minor component associated with high omega(cal) levels in Patagonia. Outlying mean index (OMI) niche analysis suggested that pH and omega(cal) conditions explained most variation in the realized niches of E. huxleyi morphotypes. The moderately calcified A morphotype exhibited the widest niche breadth (generalist), while the R/hyper-calcified morphotype exhibited a more restricted realized niche (specialist). Nevertheless, when considering an expanded sampling domain, including nearby southeast Pacific coastal and offshore waters, even the R/hyper-calcified morphotype exhibited a higher niche breadth than other closely phylogenetically related coccolithophore species. The occurrence of E. huxleyi in naturally low pH-omega(cal) environments indicates that its ecological response is plastic and capable of adaptation.
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    Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov.
    (2023) von Dassow, Peter; Mikhno, Marta; Percopo, Isabella; Orellana, Valentina Rubio; Aguilera, Victor; Alvarez, Gonzalo; Araya, Michael; Cornejo-Guzman, Sebastian; Llona, Tomas; Mardones, Jorge I.; Norambuena, Luis; Salas-Rojas, Victoria; Kooistra, Wiebe H. C. F.; Montresor, Marina; Sarno, Diana
    To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36 degrees S-30 degrees S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.
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    Do Differences in Latitudinal Distributions of Species and Organelle Haplotypes Reflect Thermal Reaction Norms Within the Emiliania/Gephyrocapsa Complex?
    (FRONTIERS MEDIA SA, 2021) von Dassow, Peter; Munoz Farias, Paula Valentina; Pinon, Sarah; Velasco Senovilla, Esther; Anguita Salinas, Simon
    The cosmopolitan phytoplankter Emiliania huxleyi contrasts with its closest relatives that are restricted to narrower latitudinal bands, making it interesting for exploring how alternative outcomes in phytoplankton range distributions arise. Mitochondrial and chloroplast haplogroups within E. huxleyi are shared with their closest relatives: Some E. huxleyi share organelle haplogroups with Gephyrocapsa parvula and G. ericsonii which inhabit lower latitudes, while other E. huxleyi share organelle haplogroups with G. muellerae, which inhabit high latitudes. We investigated whether the phylogeny of E. huxleyi organelles reflects environmental gradients, focusing on the Southeast Pacific where the different haplogroups and species co-occur. There was a high congruence between mitochondrial and chloroplast haplogroups within E. huxleyi. Haplogroup II of E. huxleyi is negatively associated with cooler less saline waters, compared to haplogroup I, both when analyzed globally and across temporal variability at the small special scale of a center of coastal upwelling at 30 degrees S. A new mitochondrial haplogroup Ib detected in coastal Chile was associated with warmer waters. In an experiment focused on inter-species comparisons, laboratory-determined thermal reaction norms were consistent with latitudinal/thermal distributions of species, with G. oceanica exhibiting warm thermal optima and tolerance and G. muellerae exhibiting cooler thermal optima and tolerances. Emiliania huxleyi haplogroups I and II tended to exhibit a wider thermal niche compared to the other Gephyrocapsa, but no differences among haplogroups within E. huxleyi were found. A second experiment, controlling for local adaptation and time in culture, found a significant difference between E. huxleyi haplogroups. The difference between I and II was of the expected sign, but not the difference between I and Ib. The differences were small (<= 1 degrees C) compared to differences reported previously within E. huxleyi by local adaptation and even in-culture evolution. Haplogroup Ib showed a narrower thermal niche. The cosmopolitanism of E. huxleyi might result from both wide-spread generalist phenotypes and specialist phenotypes, as well as a capacity for local adaptation. Thermal reaction norm differences can well explain the species distributions but poorly explain distributions among mitochondrial haplogroups within E. huxleyi. Perhaps organelle haplogroup distributions reflect historical rather than selective processes.
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    Do phytoplankton require oxygen to survive? A hypothesis and model synthesis from oxygen minimum zones
    (2023) Wong, Jane C. Y.; Raven, John A.; Aldunate, Montserrat; Silva, Sebastian; Gaitan-Espitia, Juan Diego; Vargas, Cristian A.; Ulloa, Osvaldo; von Dassow, Peter
    It is commonly known that phytoplankton have a pivotal role in marine biogeochemistry and ecosystems as carbon fixers and oxygen producers, but their response to deoxygenation has scarcely been studied. Nonetheless, in the major oceanic oxygen minimum zones (OMZs), all surface phytoplankton groups, regardless of size, disappear and are replaced by unique cyanobacteria lineages below the oxycline. To develop reasonable hypotheses to explain this pattern, we conduct a review of available information on OMZ phytoplankton, and we re-analyze previously published data (flow cytometric and hydrographic) on vertical structure of phytoplankton communities in relation to light and O-2 levels. We also review the physical constraints on O-2 acquisition as well as O-2-dependent metabolisms in phototrophs. These considerations, along with estimates of the photosynthetic capacity of phytoplankton along OMZ depth profiles using published data, suggest that top-down grazing, respiratory demand, and irradiance are insufficient to fully explain the vertical structure observed in the upper, more sunlit portions of OMZs. Photorespiration and water-water cycles are O-2-dependent pathways with low O-2 affinities. Although their metabolic roles are still poorly understood, a hypothetical dependence on such pathways by the phytoplankton adapted to the oxic ocean might explain vertical patterns in OMZs and results of laboratory experiments. This can be represented in a simple model in which the requirement for photorespiration in surface phytoplankton and O-2-inhibition of OMZ lineages reproduces the observed vertical fluorescence profiles and the replacement of phytoplankton adapted to O-2 by lineages restricted to the most O-2-deficient waters. A high O-2 requirement by modern phytoplankton would suggest a positive feedback that intensifies trends in OMZ extent and ocean oxygenation or deoxygenation, both in Earth's past and in response to current climate change.
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    Local scale extreme low pH conditions and genetic differences shape phenotypic variation in a broad dispersal copepod species
    (2023) Aguilera, Victor M.; Sepulveda, Fabiola; von Dassow, Peter; Gaitan-Espitia, Juan Diego; Mesas, Andres; Vargas, Cristian A.
    Extreme low pH events in estuaries and upwelling areas can modulate the phenotypic and genetic diversity of natural populations. To test this hypothesis, we explored the linkage between local scale extreme low pH events, genetic diversity, and variation in fecundity-related traits (body size, egg size, and egg production rate) in the broad-dispersal copepod Acartia tonsa. We assessed genetic and phenotypic characteristics of populations by contrasting extreme low pH environments (upwelling and temperate estuary) in the coastal Southeast Pacific, under natural and experimental conditions. These populations showed significant genetic differentiation with higher diversity in mitochondrial and nuclear loci (encoding mtCOI and 18S rRNA) in the estuarine population. Copepods from this population are exposed to more frequent extreme low pH events (< 7.7), and the adult females exhibit consistent phenotypic variation in body size, egg size, and egg production rate across different cohorts. Experimental acclimation to extreme low pH conditions revealed no significant differences in fecundity-related traits between A. tonsa populations. Although these results partially support our hypothesis, the experimental findings suggest other drivers might also influence phenotypic differences in the local environments.
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    Pan genome of the phytoplankton Emiliania underpins its global distribution
    (2013) Read, Betsy A.; Kegel, Jessica; Klute, Mary J.; Kuo, Alan; Lefebvre, Stephane C.; Maumus, Florian; Mayer, Christoph; Miller, John; Monier, Adam; Salamov, Asaf; Young, Jeremy; Aguilar, Maria; Claverie, Jean-Michel; Frickenhaus, Stephan; Gonzalez, Karina; Herman, Emily K.; Lin, Yao-Cheng; Napier, Johnathan; Ogata, Hiroyuki; Sarno, Analissa F.; Shmutz, Jeremy; Schroeder, Declan; de Vargas, Colomban; Verret, Frederic; von Dassow, Peter; Valentin, Klaus; Van de Peer, Yves; Wheeler, Glen; Dacks, Joel B.; Delwiche, Charles F.; Dyhrman, Sonya T.; Gloeckner, Gernot; John, Uwe; Richards, Thomas; Worden, Alexandra Z.; Zhang, Xiaoyu; Grigoriev, Igor V.; Allen, Andrew E.; Bidle, Kay; Borodovsky, M.; Bowler, C.; Brownlee, Colin; Cock, J. Mark; Elias, Marek; Gladyshev, Vadim N.; Groth, Marco; Guda, Chittibabu; Hadaegh, Ahmad; Iglesias-Rodriguez, Maria Debora; Jenkins, J.; Jones, Bethan M.; Lawson, Tracy; Leese, Florian; Lindquist, Erika; Lobanov, Alexei; Lomsadze, Alexandre; Malik, Shehre-Banoo; Marsh, Mary E.; Mackinder, Luke; Mock, Thomas; Mueller-Roeber, Bernd; Pagarete, Antonio; Parker, Micaela; Probert, Ian; Quesneville, Hadi; Raines, Christine; Rensing, Stefan A.; Riano-Pachon, Diego Mauricio; Richier, Sophie; Rokitta, Sebastian; Shiraiwa, Yoshihiro; Soanes, Darren M.; van der Giezen, Mark; Wahlund, Thomas M.; Williams, Bryony; Wilson, Willie; Wolfe, Gordon; Wurch, Louie L.
    Coccolithophores have influenced the global climate for over 200 million years(1). These marine phytoplankton can account for 20 per cent of total carbon fixation in some systems(2). They form blooms that can occupy hundreds of thousands of square kilometres and are distinguished by their elegantly sculpted calcium carbonate exoskeletons (coccoliths), rendering them visible from space(3). Although coccolithophores export carbon in the form of organic matter and calcite to the sea floor, they also release CO2 in the calcification process. Hence, they have a complex influence on the carbon cycle, driving either CO2 production or uptake, sequestration and export to the deep ocean(4). Here we report the first haptophyte reference genome, from the coccolithophore Emiliania huxleyi strain CCMP1516, and sequences from 13 additional isolates. Our analyses reveal a pan genome (core genes plus genes distributed variably between strains) probably supported by an atypical complement of repetitive sequence in the genome. Comparisons across strains demonstrate that E. huxleyi, which has long been considered a single species, harbours extensive genome variability reflected in different metabolic repertoires. Genome variability within this species complex seems to underpin its capacity both to thrive in habitats ranging from the equator to the subarctic and to form large-scale episodic blooms under a wide variety of environmental conditions.
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    Response of Phytoplankton Assemblages From Naturally Acidic Coastal Ecosystems to Elevated pCO2
    (2020) Osma, Natalia; Latorre-Melin, Laura; Jacob, Barbara; Contreras, Paulina Y.; von Dassow, Peter; Vargas, Cristian A.
    The interplay of coastal oceanographic processes usually results in partial pressures of CO2 (pCO(2)) higher than expected from the equilibrium with the atmosphere and even higher than those expected by the end of the century. Although this is a well-known situation, the natural variability of seawater chemistry at the locations from which tested organisms or communities originate is seldom considered in ocean acidification experiments. In this work, we aimed to evaluate the role of the carbonate chemistry dynamics in shaping the response of coastal phytoplankton communities to increased pCO(2) levels. The study was conducted at two coastal ecosystems off Chile, the Valdivia River estuary and the coastal upwelling ecosystem in the Arauco Gulf. We characterized the seasonal variability (winter/summer) of the hydrographic conditions, the carbonate system parameters, and the phytoplankton community structure at both sites. The results showed that carbonate chemistry dynamics in the estuary were mainly related to seasonal changes in freshwater discharges, with acidic and corrosive conditions dominating in winter. In the Arauco Gulf, these conditions were observed in summer, mainly associated with the upwelling of cold and high pCO(2) (> 1,000 mu atm) waters. Diatoms dominated the phytoplankton communities at both sites, yet the one in Valdivia was more diverse. Only certain phytoplankton groups in this latter ecosystem showed a significant correlations with the carbonate system parameters. When the impact of elevated pCO(2) levels was investigated by pCO(2) manipulation experiments, we did not observe any significant effect on the biomass of either of the two communities. Changes in the phytoplankton species composition and abundance during the incubations were related to other factors, such as competition and growth phases. Our findings highlight the importance of the natural variability of coastal ecosystems and the potential for local adaptation in determining responses of coastal phytoplankton communities to increased pCO(2) levels.
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    Response of the calcifying coccolithophore Emiliania huxleyi to low pH/high pCO2: from physiology to molecular level
    (2011) Richier, Sophie; Fiorini, Sarah; Kerros, Marie-Emmanuelle; von Dassow, Peter; Gattuso, Jean-Pierre
    The emergence of ocean acidification as a significant threat to calcifying organisms in marine ecosystems creates a pressing need to understand the physiological and molecular mechanisms by which calcification is affected by environmental parameters. We report here, for the first time, changes in gene expression induced by variations in pH/pCO(2) in the widespread and abundant coccolithophore Emiliania huxleyi. Batch cultures were subjected to increased partial pressure of CO2 (pCO(2); i.e. decreased pH), and the changes in expression of four functional gene classes directly or indirectly related to calcification were investigated. Increased pCO(2) did not affect the calcification rate and only carbonic anhydrase transcripts exhibited a significant down-regulation. Our observation that elevated pCO(2) induces only limited changes in the transcription of several transporters of calcium and bicarbonate gives new significant elements to understand cellular mechanisms underlying the early response of E. huxleyi to CO2-driven ocean acidification.
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    The Ectocarpus genome and the independent evolution of multicellularity in brown algae
    (2010) Cock, J. Mark; Sterck, Lieven; Rouze, Pierre; Scornet, Delphine; Allen, Andrew E.; Amoutzias, Grigoris; Anthouard, Veronique; Artiguenave, Francois; Aury, Jean-Marc; Badger, Jonathan H.; Beszteri, Bank; Billiau, Kenny; Bonnet, Eric; Bothwell, John H.; Bowler, Chris; Boyen, Catherine; Brownlee, Colin; Carrano, Carl J.; Charrier, Benedicte; Cho, Ga Youn; Coelho, Susana M.; Collen, Jonas; Corre, Erwan; Da Silva, Corinne; Delage, Ludovic; Delaroque, Nicolas; Dittami, Simon M.; Doulbeau, Sylvie; Elias, Marek; Farnham, Garry; Gachon, Claire M. M.; Gschloessl, Bernhard; Heesch, Svenja; Jabbari, Kamel; Jubin, Claire; Kawai, Hiroshi; Kimura, Kei; Kloareg, Bernard; Kuepper, Frithjof C.; Lang, Daniel; Le Bail, Aude; Leblanc, Catherine; Lerouge, Patrice; Lohr, Martin; Lopez, Pascal J.; Martens, Cindy; Maumus, Florian; Michel, Gurvan; Miranda-Saavedra, Diego; Morales, Julia; Moreau, Herve; Motomura, Taizo; Nagasato, Chikako; Napoli, Carolyn A.; Nelson, David R.; Nyvall-Collen, Pi; Peters, Akira F.; Pommier, Cyril; Potin, Philippe; Poulain, Julie; Quesneville, Hadi; Read, Betsy; Rensing, Stefan A.; Ritter, Andres; Rousvoal, Sylvie; Samanta, Manoj; Samson, Gaelle; Schroeder, Declan C.; Segurens, Beatrice; Strittmatter, Martina; Tonon, Thierry; Tregear, James W.; Valentin, Klaus; von Dassow, Peter; Yamagishi, Takahiro; Van de Peer, Yves; Wincker, Patrick
    Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related(1). These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae(2-5), closely related to the kelps(6,7) (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic(2) approaches to explore these and other(4,5) aspects of brown algal biology further.