Biology subjects

Schaum, C.- E.

Publications and source records attributed to Schaum, C.- E..

4 recordsLinked to original sources

bioRxiv2026

Thermal responses of Baltic Sea Ostreococcus vary in their levels of intra-and interspecific variability

Trait variation within and between phytoplankton species as well as within regions, can shape community dynamics and ecosystem processes. A better understanding of this variability will improve the prediction of future ocean scenarios and the possible resilience of different phytoplankton groups. We investigated thermal response variation within and among three Ostreococcus species--a prominent picophytoplankton genus--using 31 strains from the Baltic Sea area and eastern North Sea. Across a temperature gradient ranging from 18{degrees}C up to 32{degrees}C, we quantified growth, cell size, and a proxy for chlorophyll a (Chla) and characterized their thermal responses using modeling approaches. We further assessed how these traits vary with temperature and quantified interspecific, intraspecific and intraregional variability. Thermal performance traits showed high variability within species and regions and moderate variability between species. Ostreococcus tauri showed significantly higher thermal optimum and a trend for higher peak rates than Ostreococcus mediterraneus. Thermal safety margin and the sensitivity of growth to temperature varied substantially within all species. For size and Chla, the species showed distinct temperature responses: Ostreococcus mediterraneus exhibited highest intraspecific variability and delayed responses at colder temperatures, Ostreococcus tauri responded linearly, with the Ostreococcus mediterraneus variant showing intermediate patterns. High intraspecific variation in Ostreococcus indicates substantial evolutionary potential, while interspecific differences may contribute to ecosystem stability under changing temperatures. This is especially relevant with predicted temperature-induced community shifts favoring smaller phytoplankton groups, highlighting the need to incorporate trait variability in ecosystem models.

ecology↗

bioRxiv2020

Presence of a resident species aids invader evolution

Phytoplankton populations are intrinsically large and genetically variable, and interactions between species in these populations shape their physiological and evolutionary responses. Yet, evolutionary responses of microbial organisms in novel environments are investigated almost exclusively through the lens of species colonising new environments on their own, and invasion studies are often of short duration. Although exceptions exist, neither type of study usually measures ecologically relevant traits beyond growth rates. Here, we experimentally evolved populations of fresh- and seawater phytoplankton as monocultures (the green algae Chlamydomonas moewusii and Ostreococcus tauri, each colonising a novel, unoccupied salinity) and co-cultures (invading a novel salinity occupied by a resident species) for 200 generations. Colonisers and invaders differed in extinction risks, phenotypes (e.g. size, primary production rates) and strength of local adaptation: invaders had systematically lower extinction rates and broader salinity and temperature preferences than colonisers - regardless of the environment that the invader originated from. We emphasise that the presence of a locally adapted species has the potential to alter the invading species eco-evolutionary trajectories in a replicable way across environments of differing quality, and that the evolution of small cell size and high ROS tolerance may explain high invader fitness. To predict phytoplankton responses in a changing world, such interspecific relationships need to be accounted for.

evolutionary biology↗

bioRxiv2018

Universal metabolic constraints on the thermal tolerance of marine phytoplankton

Marine phytoplankton are responsible for over 45% of annual global net primary production. Ocean warming is expected to drive massive reorganisation of phytoplankton communities, resulting in pole-ward range shifts and sharp declines in species diversity, particularly in the tropics. The impacts of warming on phytoplankton species depend critically on their physiological sensitivity to temperature change, characterised by thermal tolerance curves. Local extinctions arise when temperatures exceed species thermal tolerance limits. The mechanisms that determine the characteristics of thermal tolerance curves (e.g. optimal and maximal temperatures) and their variability among the broad physiological diversity of marine phytoplankton are however poorly understood. Here we show that differences in the temperature responses of photosynthesis and respiration establish physiological trade-offs that constrain the thermal tolerance of 18 species of marine phytoplankton, spanning cyanobacteria as well as the red and green super-families. Across all species we found that rates of respiration were more sensitive to increasing temperature and typically had higher optimal temperatures than photosynthesis. Consequently, the fraction of photosynthetic energy available for allocation to growth (carbon-use efficiency) declined exponentially with rising temperatures with a sensitivity that was invariant among the 18 species. Furthermore, the optimal temperature of growth was generally lower than that of photosynthesis and as a result, supra-optimal declines in growth rate were associated with temperature ranges where the carbon-use efficiency exhibited accelerated declines. These highly conserved patterns demonstrate that the limits of thermal tolerance in marine phytoplankton are underpinned by common metabolic constraints linked to the differential temperature responses of photosynthesis and respiration.\n\nSignificance StatementThe impacts of warming on marine phytoplankton depend on their sensitivity to rising temperatures, yet there is currently limited understanding of the mechanisms that limit thermal tolerance among the diversity of marine phytoplankton. Using a comparative study on the dominant, ecologically important lineages of marine phytoplankton - Bacillariophyceae, Dinophyceae, Cyanophyceae, Prasinophyceae, Prymnesiophyceae - we show that rates of respiration are consistently more sensitive to increasing temperature than photosynthesis. Consequently, the fraction of photosynthetic energy available for growth declines with rising temperatures with a sensitivity that is invariant among species. Our results suggest that declines in phytoplankton performance at high temperatures are driven by universal metabolic constrains linked to rising respiratory costs eventually exceeding the supply of reduced carbon from photosynthesis.

ecology↗

bioRxiv2017

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

Diatoms 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 found that evolutionary rescue under severe warming was slow but adaptation to more realistic scenarios, where temperature increases were moderate or where they fluctuated between benign and severe conditions, was rapid. Adaption to warming was linked to major phenotypic changes in metabolism and elemental composition. Whole genome re-sequencing identified significant genetic divergence both among populations adapted to the different warming regimes and between the evolved and ancestral lineages. Consistent with the phenotypic changes, the most rapidly evolving genes were associated with transcriptional regulation, cellular response to oxidative stress and redox homeostasis. These results demonstrate that evolution of thermal tolerance in marine diatoms can be rapid, particularly in fluctuating environments, and is underpinned by major genomic and phenotypic divergence.

evolutionary biology↗