Biology subjects

Yvon-Durocher, G.

Publications and source records attributed to Yvon-Durocher, G..

10 recordsLinked to original sources

bioRxiv2025

Universal sublinear population growth density dependence unrelated to resource limitation

Growth slows as population density increases, sensitively influencing species coexistence, conservation, and resource management. This slowdown is widely attributed to declining per-capita access to energy and nutrients, and standard models of resource-limited growth predict superlinear declines of growth rate with density. However, we observed sublinear declines for 94% of 4,022 bacterial and eukaryotic growth curves. High-resolution experiments with Escherichia coli revealed a two-phase density dependence: a dominant sublinear regime that transitions to superlinear decline only very near population saturation. The sublinear pattern was invariant across initial resource concentrations, ruling out resource depletion as the cause of early slowing. Our results challenge the standard resource-limitation paradigm and identify non-resource inhibitory processes as a widespread and previously unappreciated regulator of population growth.

ecology↗

bioRxiv2025

A Novel Method to Simultaneously Estimate Bacterial Respiration and Growth from Oxygen Dynamics

Bacterial growth and respiration are fundamental metabolic processes that affect how energy is used and impact carbon sequestration at the ecosystem scale. However, these traits are usually quantified independently, growth is quantified with endpoint biomass measurements while respiration is quantified by monitoring oxygen or carbon dioxide. Because the two physiological traits are collected at different temporal and volumetric scales (hours-to-days for growth versus minutes-to-hours for respiration), reconciling them is challenging and often introduces scale-mismatch bias, obscuring causal links between metabolism and environmental drivers. In this study, we develop a novel method for quantifying the rates of bacterial growth and respiration concurrently from a single dissolved oxygen time series. Our approach introduces a model that couples exponential biomass growth with biomass-specific respiration, enabling the simultaneous inference of both rates in real time. We applied our high throughput method to 15 bacterial strains isolated from natural environments. Our approach yielded growth estimates in close agreement with measurements based on popular methods using optical density or flow cytometry (R2 > 0.9) with no evidence of taxon-specific bias. We also tested our approach in quantifying the effects of temperature on respiration, growth and carbon use-efficiency in Pseudomonas sp. Our method yielded typical unimodal thermal response curves for growth and respiration where rates were highest at moderate temperatures, while carbon-use efficiency increased from cooler temperatures, peaked around the thermal optimum ([~]30-35 {degrees}C), and declined at high temperature. By quantifying respiration and growth simultaneously and in high throughput, our approach effectively enables measurement of microbial metabolic strategies and adaptations to stress. It offers a non-invasive and scalable tool for high throughput phenotyping and studies of environmental perturbations, enabling a new class of trait-based microbial ecology that links cellular physiology to broader ecosystem function.

microbiology↗

bioRxiv2021

Species interactions amplify the temperature dependence of microbial community respiration

The respiratory release of CO2 by microbes is a dominant component of the global carbon cycle. However, large uncertainties exist about the effects of climatic warming on the respiration of microbial communities due to lack of mechanistic, empirically-tested theory that accounts for dynamic species interactions. We developed a general mathematical model which predicts that thermal sensitivity of microbial community respiration increases as species interactions become more positive, i.e., change from competition to facilitation. This is because facilitation disproportionately increases positive feedbacks between the thermal sensitivities of species-level metabolic and biomass accumulation rates at warmer temperatures. We experimentally validated this prediction in bacterial communities of 8 taxa, finding that a shift from competition to facilitation after a month of co-adaptation caused a 60% increase in the thermal sensitivity of their respiration relative to de novo communities that had not co-adapted. Thus, rapid changes in species interactions can profoundly change the temperature-dependence of microbial community respiration and should be considered in climate change models.

ecology↗

bioRxiv2019

Metabolic rates of prokaryotic microbes may inevitably rise with global warming

Understanding how the metabolic rates of prokaryotes respond to temperature is fun-damental to our understanding of how ecosystem functioning will be altered by climate change, as these micro-organisms are major contributors to global carbon efflux. Ecological metabolic theory suggests that species living at higher temperatures evolve higher growth rates than those in cooler niches due to thermodynamic constraints. Here, using a global prokaryotic dataset, we find that maximal growth rate at thermal optimum increases with temperature for mesophiles (temperature optima [lsim] 45{degrees}C), but not thermophiles ({gtrsim} 45{degrees}C). Furthermore, short-term (within-day) thermal responses of prokaryotic metabolic rates are typically more sensitive to warming than those of eukaryotes. Given that climatic warming will mostly impact ecosystems in the mesophilic temperature range, we conclude that as microbial communities adapt to higher temperatures, their metabolic rates and therefore, carbon efflux, will inevitably rise. Using a mathematical model, we illustrate the potential global impacts of these findings.

ecology↗

bioRxiv2018

Phytoplankton thermal responses adapt in the absence of hard thermodynamic constraints

To better predict how populations and communities respond to climatic temperature variation, it is necessary to understand how the shape of the response of fitness-related traits to temperature evolves (the thermal performance curve). Currently, there is disagreement about the extent to which the evolution of thermal performance curves is constrained. One school of thought has argued for the prevalence of thermodynamic constraints through enzyme kinetics, whereas another argues that adaptation can--at least partly--overcome such constraints. To shed further light on this debate, we perform a phylogenetic meta-analysis of the thermal performance curves of growth rate of phytoplankton--a globally important functional group--, controlling for environmental effects (habitat type and thermal regime). We find that thermodynamic constraints have a minor influence on the shape of the curve. In particular, we detect a very weak increase of maximum performance with the temperature at which the curve peaks, suggesting a weak "hotter-is-better" constraint. Also, instead of a constant thermal sensitivity of growth across species, as might be expected from strong constraints, we find that all aspects of the thermal performance curve evolve along the phylogeny. Our results suggest that phytoplankton thermal performance curves adapt to thermal environments largely in the absence of hard thermodynamic constraints.

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

Metabolic traits predict the effects of warming on phytoplankton competition

Understanding how changes in temperature affect interspecific competition is critical for predicting changes in ecological communities as the climate warms. Here we develop a simple theoretical model that links interspecific differences in metabolic traits, which capture the temperature-dependence of resource acquisition, to the outcome of pairwise competition in phytoplankton. We parameterised our model with metabolic traits derived from six species of freshwater phytoplankton and tested its ability to predict the outcome of competition in all pairwise combinations of the species in a factorial experiment, manipulating temperature and nutrient availability. The model correctly predicted the outcome of competition in 71% of the pairwise experiments. These results demonstrate that metabolic traits play a key role in determining how changes in temperature influence interspecific competition and lay the foundation for developing theory to predict the effects of warming in complex, multi-species communities.

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↗

bioRxiv2017

Thermal adaptation constrains the temperature dependence of ecosystem metabolism

Gross primary production (GPP) is the largest flux in the carbon cycle, yet its response to global warming is highly uncertain. The temperature sensitivity of GPP is directly linked to photosynthetic physiology, but the response of GPP to warming over longer timescales could also be shaped by ecological and evolutionary processes that drive variation community structure and functional trait distributions. Here, we show that selection on photosynthetic traits within and across taxa dampen the effects of temperature on GPP across a catchment of geothermally heated streams. Autotrophs from cold streams had higher photosynthetic rates and after accounting for differences in biomass among sites, rates of ecosystem-level GPP were independent of temperature, despite a 20 {o}C thermal gradient. Our results suggest that thermal adaptation constrains the long-term temperature dependence of GPP, and highlights the importance of considering physiological, ecological and evolutionary mechanisms when predicting how ecosystem-level processes respond to warming.

ecology↗

bioRxiv2017

Adaptation to warming increases the strength of an algal-grazer interaction in naturally heated streams

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 a [~]10{degrees}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, the wandering snail Radix balthica, and a common algal resource. Populations from a warm stream ([~]28{degrees}C) had higher maximal metabolic rates and optimal temperatures than their counterparts from a cold stream ([~]17{degrees}C). We found that metabolic rates of the population originating from a 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 of grazers from the warm stream were always higher than those of grazers from the cold stream. These findings suggest that warming can increase the strength of algal-grazer interactions through the thermodynamic effects of higher temperatures on physiological rates as well as through correlated increases in per capita metabolism and consumption.

ecology↗