Biology subjects

Litchman, E.

Publications and source records attributed to Litchman, E..

9 recordsLinked to original sources

bioRxiv2025

Warm-loving species perform well under limiting resources:trait combinations for future climate

Ecosystems are warming alongside shifts in other abiotic factors, leading to interactive effects on populations and communities. This underscores the importance of studying how organisms respond to multiple environmental changes simultaneously. In aquatic ecosystems, as surface waters of lakes and oceans warm, longer and stronger periods of thermal stratification lead to changes in resource (light and nutrient) availability. We investigate the combined effect of temperature and resource availability on 19 populations (comprising 17 species) of freshwater phytoplankton to examine how temperature influences the minimum resource requirements (and Monod parameters) for light, nitrogen, and phosphorus. We also evaluate how resource availability affects each populations thermal traits (i.e. thermal performance curve -TPC-parameters). When averaged across all populations, the requirements for light and phosphorus tended to display a U-shaped relationship along temperatures. Individual populations varied greatly in their responses to temperature, leading to shifts in the identity of the best competitor across the thermal gradient, particularly for nitrogen and phosphorus. TPC responses to resource limitation were highly variable, but thermal optima and maxima of individual populations often decreased with resource limitation, and thermal breadths (range where growth is 80% or more of its maximum) often increased due to a flattening of TPCs. Across all populations and resource types, the maximum optimum temperature across resource levels (maximum Topt) tended to be positively correlated with the temperature at which they had the lowest resource requirements (minimum R*). However, the temperature at which populations were the best competitors tended to be [~]5 {degrees}C colder on average than the temperature at which they grew the fastest. The populations with the highest thermal optima also had the lowest minimum resource requirements. Our findings reveal trait associations suggesting that some taxa already exhibit trait combinations that would support high performance under future warm and resource-limited conditions.

ecology↗

bioRxiv2025

New niches for larger phytoplankton in a warmer, more resource-limited ocean

Warming and nutrient limitation are major stressors that affect primary production in the ocean, with cascading impacts on the food web. Yet, we lack a mechanistic understanding of how phytoplankton manage multiple stressors and the implications of these responses for phytoplankton biogeography. By combining theory, proteome allocation modeling, and climate projections, we identified two potential competing strategies for multi-stressor growth: (1) nutrient efficient smaller cells, or (2) heat-tolerant larger cells. We found that Prochlorococcus are more vulnerable in warmer, "heat-stressed", tropical regions due to greater heat sensitivity and lower lipid storage capacity to buffer oxidative stress, indicating a potential ecological niche for larger phytoplankton with lower sensitivity to oxidative stress, such as Synechococcus and picoeukaryotes. Our findings advocate for the inclusion of phytoplankton heat-stress responses in global models to more accurately predict their ecological niches as the climate warms.

ecology↗

bioRxiv2024

Evolution of thermal tolerance in marine diatoms: Metabolic strategies under heat stress.

In the last decade, numerous laboratory experiments have demonstrated that when marine phytoplankton are exposed to thermal stress, they can evolve high temperature tolerance in a short time (weeks to months). This evolutionary potential may ensure the persistence of marine phytoplankton species under current and future global warming. However, the effect of such adaptation on the phytoplankton interaction with the environment and other organisms depends on how cellular metabolism shifts during the evolutionary process. In order to elucidate which cellular strategies allow the emergence of thermo-tolerant populations, we analyzed the proteomics response of a marine diatom (Chaetoceros simplex) to both thermal acclimation and evolutionary adaptation. We found that high temperature-tolerant populations exhibit a conservative cellular strategy when acclimated to high, above-optimal temperature, where recycling and reallocation is favored at the expense of new structures biosynthesis. While this strategy gives the populations that evolved high temperature tolerance an advantage under thermal stress, the shift to resource reallocation may explain the absence of high-temperature adaptation when cells are exposed to low nitrate availability.

ecology↗

bioRxiv2024

How interactions between temperature and resources scale from populations to communities

Temperature and resources are fundamental factors that determine the ability of organisms to function and survive, while influencing their development, growth, and reproduction. Major bodies of ecological theory have emerged, largely independently, to address temperature and resource effects. It remains a major challenge to unite these ideas and determine the interactive effects of temperature and resources on ecological patterns and processes, and their consequences across ecological scales. Here, we propose a simple, physiologically motivated model capturing the interactive effects of temperature and resources (including inorganic nutrients and light) on the growth of microbial ectotherms over multiple ecological scales. From this model we derive a set of key predictions. At the population level, we predict (i) interactive effects of resource limitation on thermal traits, (ii) consistent differences in the temperature sensitivity of auto- and heterotrophs, and (iii) the existence of specific tradeoffs between traits that determine the shape of thermal performance curves. At the community level, we derive predictions for (iv) how limitation by nutrients and light can change the relationship between temperature and productivity. All four predictions are upheld, based on our analyses of a large compilation of laboratory data on microbial growth, as well as field experiments with marine phytoplankton communities. Collectively, our modeling framework provides a new way of thinking about the interplay between two fundamental aspects of life -- temperature and resources -- and how they constrain and structure ecological properties across scales. Providing links between population and community responses to simultaneous changes in abiotic factors is essential to anticipating the multifaceted effects of global change.

ecology↗

bioRxiv2022

A general framework for species-abundance distributions: linking traits and dispersal to explain commonness and rarity

Species-abundance distributions (SADs) describe the spectrum of commonness and rarity in a community. Beyond the universal observation that most species are rare and only a few common, more-precise description of SAD shape is controversial. Furthermore, the mechanisms behind SADs and how they vary along environmental gradients remain unresolved. We lack a general non-neutral theory of SADs. Here we develop a trait-based framework, focusing on a local community coupled to the region by dispersal. The balance of immigration and exclusion determines abundances, which vary over orders-of-magnitude. Under stabilizing selection, the local trait-abundance distribution (TAD) reflects a transformation of the regional TAD. The left-tail of the SAD depends on scaling exponents of the exclusion function and the regional species pool. More-complex local dynamics can lead to multimodal TADs and SADs. Connecting SADs with trait-based ecological theory provides a way to generate more-testable hypotheses on the controls over commonness and rarity in communities.

ecology↗

bioRxiv2020

Dual thermal ecotypes detected within a nearly genetically-identical population of the unicellular marine cyanobacterium Synechococcus

The extent and ecological significance of intraspecific diversity within marine microbial populations is still poorly understood, and it remains unclear if such strain-level microdiversity will affect fitness and persistence in a rapidly changing ocean environment. In this study, we cultured 11 sympatric strains of the ubiquitous marine picocyanobacterium Synechococcus isolated from a Narragansett Bay (Rhode Island, USA) phytoplankton community thermal selection experiment. Despite all 11 isolates being highly similar (with average nucleotide identities of >99.9%, with 98.6-100% of the genome aligning), thermal performance curves revealed selection at warm and cool temperatures had subdivided the initial population into thermotypes with pronounced differences in maximum growth temperatures. Within the fine-scale genetic diversity that did exist within this population, the two divergent thermal ecotypes differed at a locus containing genes for the phycobilisome antenna complex. Our study demonstrates that present-day marine microbial populations can contain microdiversity in the form of cryptic but environmentally-relevant thermotypes that may increase their resilience to future rising temperatures. SignificanceNumerous studies exist comparing the responses of distinct taxonomic groups of marine microbes to a warming ocean (interspecific thermal diversity). For example, Synechococcus, a nearly globally distributed unicellular marine picocyanobacterium that makes significant contributions to oceanic primary productivity, contains numerous taxonomically distinct lineages with well documented temperature relationships. Little is known though about the diversity of functional responses to temperature within a given population where genetic similarity is high (intraspecific thermal diversity). This study suggests that understanding the extent of this functional intraspecific microdiversity is an essential prerequisite to predicting the resilience of biogeochemically essential microbial groups such as marine Synechococcus to a changing climate.

microbiology↗

bioRxiv2020

Shape matters: cell geometry determines phytoplankton diversity

Size and shape profoundly influence an organisms ecophysiological performance and evolutionary fitness, suggesting a link between morphology and diversity. However, not much is known about how body shape is related to taxonomic richness, especially in microbes. Here we analyse global datasets of unicellular marine phytoplankton, a major group of primary producers with an exceptional diversity of cell sizes and shapes and, additionally, heterotrophic protists. Using two measures of cell shape elongation, we quantify taxonomic diversity as a function of cell size and shape. We find that cells of intermediate volume have the greatest shape variation, from oblate to extremely elongated forms, while small and large cells are mostly compact (e.g., spherical or cubic). Taxonomic diversity is strongly related to cell elongation and cell volume, together explaining up to 92% of total variance. Taxonomic diversity decays exponentially with cell elongation and displays a log-normal dependence on cell volume, peaking for intermediate-volume cells with compact shapes. These previously unreported broad patterns in phytoplankton diversity reveal selective pressures and ecophysiological constraints on the geometry of phytoplankton cells which may improve our understanding of marine ecology and the evolutionary rules of life.

ecology↗

bioRxiv2019

Environmental drivers define contrasting microbial habitats, diversity and functional redundancy in Lake Baikal, Siberia

Understanding how microbial communities respond to environmental change requires knowing the main drivers of their structure, diversity and potential resilience. Lake Baikal is the worlds most ancient, deep, voluminous, and biodiverse lake, holding 20 percent of unfrozen fresh water that is undergoing rapid warming. Despite its global importance, little is known about Baikals bacterioplankton communities and their drivers. In this extensive survey, we show that temperature, along with stratification, nutrients, and dissolved oxygen, but not geographic distance, define major microbial habitats and community similarity. Mixed layer and deep water communities exhibited contrasting patterns of richness, diversity and evenness, and comprised different cohesive modules in the whole Baikal OTU co-occurrence network. The networks small-world properties indicated likely resistance to perturbations but sensitivity to abundance changes of central, most connected OTUs. Previous studies showed Baikal water temperature rising by over 1.2{degrees}C since 1946, and this trend is predicted to accelerate. Because temperature emerged as the most significant predictor of the mixed layer community structure, we hypothesize that it is most likely to drive future community changes. Understanding how temperature and other abiotic factors structure microbial communities in this and other rapidly changing ecosystems will allow better predictions of ecosystem responses to anthropogenic stressors.

ecology↗

bioRxiv2017

Temperature selection drives evolution of function-valued traits in a marine diatom

Rapid evolution in response to environmental change will likely be a driving force determining the distribution of species and the structure of communities across the biosphere in coming decades. This is especially true of microorganisms, many of which may be able to evolve in step with rising temperatures. An ecologically indispensable group of microorganisms with great potential for rapid thermal adaptation are the phytoplankton, the diverse photosynthetic microbes forming the foundation of most aquatic food webs. We tested the capacity of a globally important phytoplankton species, the marine diatom Thalassiosira pseudonana, for rapid evolution in response to temperature. Evolution of replicate populations at 16 and 31{degrees}C for 350-450 generations led to significant divergence in several traits associated with T. pseudonanas thermal reaction norm (TRN) for per-capita population growth, as well as in its competitive ability for nitrogen (commonly limiting in marine systems). Of particular interest were evolution of the optimum temperature for growth, the upper critical temperature, and the derivative of the TRN, an indicator of potential tradeoffs resulting from local adaptation to temperature. This study offers a broad examination of the evolution of the thermal reaction norm and how modes of TRN variation may govern a populations long-term physiological, ecological, and biogeographic response to global climate change.

evolutionary biology↗