The hidden flows within species: Phytoplankton population dynamics in Arctic assemblages

Progressing climate change and concurrent alterations of environmental conditions pose challenges of adaptation on organisms and ecosystems, especially in rapidly changing places like the Arctic. While more diverse systems are usually considered to be more resilient, biodiversity does not only describe the number of species, but can also consist of diverse individuals within a species. Especially in protists, with large census sizes and fast proliferation, intraspecific lineage sorting can be an important mechanism of plasticity and trait adjustment. For phytoplankton communities at the base of the foodweb, physiological acclimation and species shifts are frequently described, but intraspecific composition and diversity are methodologically still difficult to resolve, especially in diverse natural contexts and at temporal resolution. Therefore, our knowledge on the functioning and importance of intraspecific selection dynamics in phytoplankton is still limited. In recent years, we have developed and applied a new, high throughput methodology for phytoplankton population composition, which can make temporal and spatial population dynamics visible that were before extremely difficult to resolve. Next to experiments with natural phytoplankton communities and artificial populations under controlled settings, a time-series of Arctic spring blooms has been investigated towards the year-to year composition of species but also of intraspecific populations of a dominant diatom. Datasets emerging now thanks to such novel technologies can offer new, more comprehensive perspectives on our understanding of the mechanisms and results of microevolution and local adaptation, and can reveal formerly hidden patterns of species’ strategies of persistence and development

Resilience and adaptive mechanisms of Arctic phytoplankton under heatwaves: Acclimation, microevolution and community resilience

Trait adjustments of phytoplankton communities to changing environmental conditions can take place through responses on several fundamental ecological levels. These include physiological acclimation of single genotypes, evolution through sorting among genotypes of the same species, and selection within the entire multi-species community. Which of these different levels responds to environmental change can have large ecological and biogeochemical implications, but especially in protists, these levels are extremely difficult to disentangle. Arctic phytoplankton at base of the foodweb in one of the most rapidly warming regions on the planet, are faced with especially large changes, but often show high resilience. Among these changes are more frequent and intense heatwaves, which expose organisms to vast temperature fluctuations. In dedicated experimental setups of different ecological complexity, we investigated how phytoplankton responds and adjusts to heatwaves, and on which of the mentioned levels shifts can be observed. We resolved not only physiological features and productivity, but also composition on the species as well as the intraspecific level, using a novel molecular approach to efficiently examine the composition of protist populations in diverse contexts. This setup provides a comprehensive approach to investigate how phytoplankton communities respond to stable and fluctuating temperature scenarios, physiologically and ecologically

Environmental fluctuations accelerate molecular evolution of thermal tolerance in a marine diatom

This is the final version of the article. Available from Springer Nature via the DOI in this recordThe publisher correction to this article is in ORE at: http://hdl.handle.net/10871/34487Diatoms contribute roughly 20% of global primary production, but the factors determining their ability to adapt to global warming are unknown. Here we quantify the capacity for adaptation to warming in the marine diatom Thalassiosira pseudonana. We find that evolutionary rescue under severe (32 °C) warming is slow, but adaptation to more realistic scenarios where temperature increases are moderate (26 °C) or fluctuate between benign and severe conditions is rapid and linked to phenotypic changes in metabolic traits and elemental composition. Whole-genome re-sequencing identifies genetic divergence among populations selected in the different warming regimes and between the evolved and ancestral lineages. Consistent with the phenotypic changes, the most rapidly evolving genes are associated with transcriptional regulation, cellular responses to oxidative stress and redox homeostasis. These results demonstrate that the evolution of thermal tolerance in marine diatoms can be rapid, particularly in fluctuating environments, and is underpinned by major genomic and phenotypic change.This study was funded by a Leverhulme Trust research grant (RPG-2013-335). Whole genome re-sequencing was carried out at Exeter Sequencing Service and Computational core facilities at the University of Exeter, where Dr. Karen Moore, Dr. Audrey Farbos, Paul O’Neill, and Dr. Konrad Paszkiewicz lead the handling of the samples. Exeter Squencing Services are supported by Medical Research Council Clinical Infrastructure award (MR/M008924/1), Wellcome Trust Institutional Strategic Support Fund (WT097835MF), Wellcome Trust Multi User Equipment Award (WT101650MA), and BBSRC LOLA award (BB/K003240/1)

Publisher Correction: Environmental fluctuations accelerate molecular evolution of thermal tolerance in a marine diatom

The article for which this is the publisher correction is in ORE at: http://hdl.handle.net/10871/32652The PDF version of this Article was updated shortly after publication following an error which resulted in the Φ symbol being omitted from the left hand side of equation 8. The HTML version was correct from the time of publication

Role of carbon allocation efficiency in the temperature dependence of autotroph growth rate

To predict how plant growth rate will respond to temperature requires understanding how temperature drives the underlying metabolic rates. Although past studies have considered the temperature dependences of photosynthesis and respiration rates underlying growth, they have largely overlooked the temperature dependence of carbon allocation efficiency. By combining a mathematical model that links exponential growth rate of a population of photosynthetic cells to photosynthesis, respiration, and carbon allocation; to an experiment on a freshwater alga; and to a database covering a wide range of taxa, we show that allocation efficiency is crucial for predicting how growth rates will respond to temperature change across aquatic and terrestrial autotrophs, at both short and long (evolutionary) timescales

Temperature-driven selection on metabolic traits increases the strength of an algal-grazer interaction in naturally warmed streams

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Trophic interactions are important determinants of the structure and functioning of ecosystems. As the metabolism and consumption rates of ectotherms increase sharply with temperature, there are major concerns that global warming will increase the strength of trophic interactions, destabilizing food webs, and altering ecosystem structure and function. We used geothermally warmed streams that span an 11°C temperature gradient to investigate the interplay between temperature-driven selection on traits related to metabolism and resource acquisition, and the interaction strength between the keystone gastropod grazer, Radix balthica, and a common algal resource. Populations from a warm stream (~28°C) had higher maximal metabolic rates and optimal temperatures than their counterparts from a cold stream (~17°C). We found that metabolic rates of the population originating from the warmer stream were higher across all measurement temperatures. A reciprocal transplant experiment demonstrated that the interaction strengths between the grazer and its algal resource were highest for both populations when transplanted into the warm stream. In line with the thermal dependence of respiration, interaction strengths involving grazers from the warm stream were always higher than those with grazers from the cold stream. These results imply that increases in metabolism and resource consumption mediated by the direct, thermodynamic effects of higher temperatures on physiological rates are not mitigated by metabolic compensation in the long-term, and suggest that warming will increase the strength of algal-grazer interactions with likely knock-on effects for the biodiversity and productivity of aquatic ecosystems. This article is protected by copyright. All rights reserved.Leverhulme Trust Research , Grant/AwardNumber: RP G-2013-335; ERC-StG, Grant/Award Number : ERC-StG 67727

Variability approaching the thermal limits can drive diatom community dynamics

Organismal distributions are largely mediated by temperature, suggesting thermal trait variability plays a key role in defining species\u27 niches. We employed a trait‐based approach to better understand how inter‐ and intraspecific thermal trait variability could explain diatom community dynamics using 24 strains from 5 species in the diatom genusSkeletonema, isolated from Narragansett Bay (NBay), where this genus can comprise up to 99% of the microplankton. Strain‐specific thermal reaction norms were generated using growth rates obtained at temperatures ranging from −2°C to 36°C. Comparison of thermal reaction norms revealed inter‐ and intraspecific similarities in the thermal optima, but significant differences approaching the thermal limits. Cellular elemental composition was determined for two thermally differentiated species and again, the most variation occurred approaching the thermal limits. To determine the potential impact of interspecific variability on community composition, a species succession model was formulated utilizing each species\u27 empirically determined thermal reaction norm and historical temperature data from NBay. Seasonal succession in the modeled community resembled the timing of species occurrence in the field, but not species\u27 relative abundance. The model correctly predicted the timing of the dominant winter–spring species, Skeletonema marinoi, within 0–14 d of its observed peak occurrence in the field. Interspecific variability approaching the thermal limits provides an alternative mechanism for temporal diatom succession, leads to altered cellular elemental composition, and thus has the potential to influence carbon flux and nutrient cycling, suggesting that growth approaching the thermal limits be incorporated into both empirical and modeling efforts in the future

A method for the reconstruction of unknown non-monotonic growth functions in the chemostat

We propose an adaptive control law that allows one to identify unstable steady states of the open-loop system in the single-species chemostat model without the knowledge of the growth function. We then show how one can use this control law to trace out (reconstruct) the whole graph of the growth function. The process of tracing out the graph can be performed either continuously or step-wise. We present and compare both approaches. Even in the case of two species in competition, which is not directly accessible with our approach due to lack of controllability, feedback control improves identifiability of the non-dominant growth rate.Comment: expansion of ideas from proceedings paper (17 pages, 8 figures), proceedings paper is version v

Immunogenicity and safety of a quadrivalent high-dose inactivated influenza vaccine compared with a standard-dose quadrivalent influenza vaccine in healthy people aged 60 years or older: a randomized Phase III trial

A quadrivalent high-dose inactivated influenza vaccine (IIV4-HD) is licensed for adults 6565 y of age based on immunogenicity and efficacy studies. However, IIV4-HD has not been evaluated in adults aged 60\u201364 y. This study compared immunogenicity and safety of IIV4-HD with a standard-dose quadrivalent influenza vaccine (IIV4-SD) in adults aged 6560 y. This Phase III, randomized, modified double-blind, active-controlled study enrolled 1,528 participants aged 6560 y, randomized 1:1 to a single injection of IIV4-HD or IIV4-SD. Hemagglutination inhibition (HAI) geometric mean titers (GMTs) were measured at baseline and D 28 and seroconversion assessed. Safety was described for 180 d after vaccination. The primary immunogenicity objective was superiority of IIV4-HD versus IIV4-SD, for all four influenza strains 28 d post vaccination in participants aged 60\u201364 and 6565 y. IIV4-HD induced a superior immune response versus IIV4-SD in terms of GMTs in participants aged 60\u201364 y and those aged 6565 y for all four influenza strains. IIV4-HD induced higher GMTs in those aged 60\u201364 y than those aged 6565 y. Seroconversion rates were higher for IIV4-HD versus IIV4-SD in each age-group for all influenza strains. Both vaccines were well tolerated in participants 6560 y of age, with no safety concerns identified. More solicited reactions were reported with IIV4-HD than with IIV4-SD. IIV4-HD provided superior immunogenicity versus IIV4-SD and was well tolerated in adults aged 6560 y. IIV4-HD is assumed to offer improved protection against influenza compared with IIV4-SD in adults aged 6560 y, as was previously assessed for adults aged 6565 y