Elena Litchman | Michigan State University (original) (raw)

Papers by Elena Litchman

This dataset represents microscopy cell counts from multivariate mesocosm experiments conducted w... more This dataset represents microscopy cell counts from multivariate mesocosm experiments conducted with a natural phytoplankton community from Narragansett Bay, RI. These data were assessed in Anderson et al. The Interactive Effects of Temperature and Nutrients on a Spring Phytoplankton Community (in prep).

Supplementary statistical methods.

Species in the analysis, trait data, and sources.

A table defining parameters and variables and three figures summarizing methods and results of as... more A table defining parameters and variables and three figures summarizing methods and results of assays used to obtain model parameter estimates.

Environments change, for both natural and anthropogenic reasons, which can threaten species persi... more Environments change, for both natural and anthropogenic reasons, which can threaten species persistence. Evolutionary adaptation is a potentially powerful mechanism to allow species to persist in these changing environments. To determine the conditions under which adaptation will prevent extinction (evolutionary rescue), classic quantitative genetics models have assumed a constantly changing environment. They predict that species traits will track a moving environmental optimum with a lag that approaches a constant. If fitness is negative at this lag, the species will go extinct. There have been many elaborations of these models incorporating increased genetic realism. Here, we review and explore the consequences of four ecological complications: non-quadratic fitness functions, interacting density- and trait-dependence, species interactions and fundamental limits to adaptation. We show that non-quadratic fitness functions can result in evolutionary tipping points and existential cr...

Philosophical Transactions of the Royal Society B: Biological Sciences, 2020

Predicting the effects of multiple global change stressors on microbial communities remains a cha... more Predicting the effects of multiple global change stressors on microbial communities remains a challenge because of the complex interactions among those factors. Here, we explore the combined effects of major global change stressors on nutrient acquisition traits in marine phytoplankton. Nutrient limitation constrains phytoplankton production in large parts of the present-day oceans, and is expected to increase owing to climate change, potentially favouring small phytoplankton that are better adapted to oligotrophic conditions. However, other stressors, such as elevated p CO 2 , rising temperatures and higher light levels, may reduce general metabolic and photosynthetic costs, allowing the reallocation of energy to the acquisition of increasingly limiting nutrients. We propose that this energy reallocation in response to major global change stressors may be more effective in large-celled phytoplankton species and, thus, could indirectly benefit large-more than small-celled phytoplank...

Fatty acid profiles per cell of replicate populations of Thalassiosira pseudonana, selected at 16... more Fatty acid profiles per cell of replicate populations of Thalassiosira pseudonana, selected at 16 and 31C for ~500 generations and assayed at 4 temperatures

Journal of Plankton Research, 2021

Body size is an important trait of any organism, including phytoplankton, because it affects phys... more Body size is an important trait of any organism, including phytoplankton, because it affects physiological and morphological performance, reproduction, population growth rate and competitive interactions. Understanding how interacting top-down and bottom-up factors influence phytoplankton cell size in different aquatic environments is still a challenge. Structural equation modeling (SEM) is a comprehensive multivariate statistical tool for detecting cause–effect relationship among different variables and their hierarchical structure in complex networks (e.g. trophic interactions in ecosystems). Here, several SEM models were employed to investigate the direct and indirect interaction pathways affecting the phytoplankton size structure in 44 mostly eutrophic and hypereutrophic permanent lakes in western Turkey. Among the 15 environmental variables tested, only rotifers and Carlson’s Trophic Index (TSI) had significant direct positive effect on the mean phytoplankton size and size vari...

Journal of Geophysical Research: Biogeosciences, 2021

Size and shape profoundly influence an organism's ecophysiological performance and evolutionary f... more Size and shape profoundly influence an organism's 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, in particular in the microbial realm. Here we analyse global datasets of unicellular phytoplankton, a major photosynthetic group with an exceptional diversity of cell sizes and shapes. 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 with cell elongation and cell volume, with both traits, in combination, explaining up to 92% of total variance. Diversity decays exponentially with cell elongation and displays a log-normal dependence on cell volume, peaking for compact, intermediate-volume cells. 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.

Global Change Biology, 2018

Rapid evolution in response to environmental change will likely be a driving force determining th... more Rapid evolution in response to environmental change will likely be a driving force determining the distribution of species across the biosphere in coming decades. This is especially true of microorganisms, many of which may evolve in step with warming, including phytoplankton, the diverse photosynthetic microbes forming the foundation of most aquatic food webs. Here we tested the capacity of a globally important, model marine diatom Thalassiosira pseudonana, for rapid evolution in response to temperature. Selection at 16 and 31°C for 350 generations led to significant divergence in several temperature response traits, demonstrating local adaptation and the existence of trade-offs associated with adaptation to different temperatures. In contrast, competitive ability for nitrogen (commonly limiting in marine systems), measured after 450 generations of temperature selection, did not diverge in a systematic way between temperatures. This study shows how rapid thermal adaptation affects key temperature and nutrient traits and, thus, a population's long-term physiological, ecological, and biogeographic response to climate change.

Rapid evolution in response to environmental change will likely be a driving force determining th... more 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 °C for 350-450 generations led to significant divergence in several traits associated with T. pseudonana's thermal reaction norm (TRN) for per-capita population growth, as well as in its competitive ability for nitrogen (commonly limiting in marine systems). Of...

Aquatic Ecology, 2017

Rising lake temperatures and changing nutrient inputs are believed to favour the spread of a toxi... more Rising lake temperatures and changing nutrient inputs are believed to favour the spread of a toxic invasive cyanobacterium, Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju, in temperate lakes. However, most evidence for these hypotheses is observational or based on physiological measurements in monocultures. We lack clear experimental evidence relating temperature and nutrients to the competitive success of C. raciborskii. To address this, we performed a 2 9 2 factorial laboratory experiment to study the dynamics of mixed phytoplankton communities subjected to different levels of temperature and phosphorus over 51 days. We allowed C. raciborskii to compete with ten different species from major taxonomic groups (diatoms, green algae, cryptophytes, and cyanobacteria) typical of temperate lakes, under low and high summer temperatures (25 and 30°C) at two levels of phosphorus supply (1 and 25 lmol L-1). Cylindrospermopsis raciborskii dominated the communities and strongly decreased diversity under low-phosphorus conditions, consistent with the hypothesis that it is a good phosphorus competitor. In contrast, it remained extremely rare in high-phosphorus conditions, where fast-growing green algae dominated. Surprisingly, temperature played a negligible role in influencing community composition, suggesting that changes in summer temperature may not be important in determining C. raciborskii's spread.

Journal of Plankton Research, 2015

Marine phytoplankton are a taxonomically and functionally diverse group of organisms that are key... more Marine phytoplankton are a taxonomically and functionally diverse group of organisms that are key players in the most important biogeochemical cycles. Phytoplankton taxa show different resource utilization strategies (e.g. nutrient uptake rates and cellular allocation) and traits. Therefore, acknowledging this diversity is crucial to understanding how elemental cycles operate, including the origin and dynamics of elemental ratios. In this paper, we focus on trait-based models as tools to study the role of phytoplankton diversity in the stoichiometric phenomenology observed in the laboratory and in the open ocean. We offer a compilation of known empirical results on stoichiometry, and summarize how trait-based approaches have attempted to replicate these results. By contrasting the different ecological and evolutionary approaches available in the literature, we explore the strengths and limitations of the existing models. We thus try to identify existing gaps and challenges, and point to potential new directions that can be explored in order to fill these gaps. We aim to highlight the potential of including diversity explicitly in our modelling approaches, which can help us gain important knowledge about changes in local and global stoichiometric patterns.

Journal of Ecology, 2015

1. Phytoplankton are key players in the global carbon cycle, contributing about half of global pr... more 1. Phytoplankton are key players in the global carbon cycle, contributing about half of global primary productivity. Within the phytoplankton, functional groups (characterized by distinct traits) have impacts on other major biogeochemical cycles, such as nitrogen, phosphorus and silica. Changes in phytoplankton community structure, resulting from the unique environmental sensitivities of these groups, may significantly alter elemental cycling from local to global scales. 2. We review key traits that distinguish major phytoplankton functional groups, how they affect biogeochemistry and how the links between community structure and biogeochemical cycles are modelled. 3. Finally, we explore how global environmental change will affect phytoplankton communities, from the traits of individual species to the relative abundance of functional groups, and how that, in turn, may alter biogeochemical cycles. 4. Synthesis. We can increase our mechanistic understanding of the links between the community structure of primary producers and biogeochemistry by focusing on traits determining functional group responses to the environment (response traits) and their biogeochemical functions (effect traits). Identifying trade-offs including allometric and phylogenetic constraints among traits will help parameterize predictive biogeochemical models, enhancing our ability to anticipate the consequences of global change.

Philosophical Transactions of the Royal Society B: Biological Sciences, 2020

Environments change, for both natural and anthropogenic reasons, which can threaten species persi... more Environments change, for both natural and anthropogenic reasons, which can threaten species persistence. Evolutionary adaptation is a potentially powerful mechanism to allow species to persist in these changing environments. To determine the conditions under which adaptation will prevent extinction (evolutionary rescue), classic quantitative genetics models have assumed a constantly changing environment. They predict that species traits will track a moving environmental optimum with a lag that approaches a constant. If fitness is negative at this lag, the species will go extinct. There have been many elaborations of these models incorporating increased genetic realism. Here, we review and explore the consequences of four ecological complications: non-quadratic fitness functions, interacting density- and trait-dependence, species interactions and fundamental limits to adaptation. We show that non-quadratic fitness functions can result in evolutionary tipping points and existential cr...

This dataset represents microscopy cell counts from multivariate mesocosm experiments conducted w... more This dataset represents microscopy cell counts from multivariate mesocosm experiments conducted with a natural phytoplankton community from Narragansett Bay, RI. These data were assessed in Anderson et al. The Interactive Effects of Temperature and Nutrients on a Spring Phytoplankton Community (in prep).

Supplementary statistical methods.

Species in the analysis, trait data, and sources.

A table defining parameters and variables and three figures summarizing methods and results of as... more A table defining parameters and variables and three figures summarizing methods and results of assays used to obtain model parameter estimates.

Environments change, for both natural and anthropogenic reasons, which can threaten species persi... more Environments change, for both natural and anthropogenic reasons, which can threaten species persistence. Evolutionary adaptation is a potentially powerful mechanism to allow species to persist in these changing environments. To determine the conditions under which adaptation will prevent extinction (evolutionary rescue), classic quantitative genetics models have assumed a constantly changing environment. They predict that species traits will track a moving environmental optimum with a lag that approaches a constant. If fitness is negative at this lag, the species will go extinct. There have been many elaborations of these models incorporating increased genetic realism. Here, we review and explore the consequences of four ecological complications: non-quadratic fitness functions, interacting density- and trait-dependence, species interactions and fundamental limits to adaptation. We show that non-quadratic fitness functions can result in evolutionary tipping points and existential cr...

Philosophical Transactions of the Royal Society B: Biological Sciences, 2020

Predicting the effects of multiple global change stressors on microbial communities remains a cha... more Predicting the effects of multiple global change stressors on microbial communities remains a challenge because of the complex interactions among those factors. Here, we explore the combined effects of major global change stressors on nutrient acquisition traits in marine phytoplankton. Nutrient limitation constrains phytoplankton production in large parts of the present-day oceans, and is expected to increase owing to climate change, potentially favouring small phytoplankton that are better adapted to oligotrophic conditions. However, other stressors, such as elevated p CO 2 , rising temperatures and higher light levels, may reduce general metabolic and photosynthetic costs, allowing the reallocation of energy to the acquisition of increasingly limiting nutrients. We propose that this energy reallocation in response to major global change stressors may be more effective in large-celled phytoplankton species and, thus, could indirectly benefit large-more than small-celled phytoplank...

Fatty acid profiles per cell of replicate populations of Thalassiosira pseudonana, selected at 16... more Fatty acid profiles per cell of replicate populations of Thalassiosira pseudonana, selected at 16 and 31C for ~500 generations and assayed at 4 temperatures

Journal of Plankton Research, 2021

Body size is an important trait of any organism, including phytoplankton, because it affects phys... more Body size is an important trait of any organism, including phytoplankton, because it affects physiological and morphological performance, reproduction, population growth rate and competitive interactions. Understanding how interacting top-down and bottom-up factors influence phytoplankton cell size in different aquatic environments is still a challenge. Structural equation modeling (SEM) is a comprehensive multivariate statistical tool for detecting cause–effect relationship among different variables and their hierarchical structure in complex networks (e.g. trophic interactions in ecosystems). Here, several SEM models were employed to investigate the direct and indirect interaction pathways affecting the phytoplankton size structure in 44 mostly eutrophic and hypereutrophic permanent lakes in western Turkey. Among the 15 environmental variables tested, only rotifers and Carlson’s Trophic Index (TSI) had significant direct positive effect on the mean phytoplankton size and size vari...

Journal of Geophysical Research: Biogeosciences, 2021

Size and shape profoundly influence an organism's ecophysiological performance and evolutionary f... more Size and shape profoundly influence an organism's 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, in particular in the microbial realm. Here we analyse global datasets of unicellular phytoplankton, a major photosynthetic group with an exceptional diversity of cell sizes and shapes. 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 with cell elongation and cell volume, with both traits, in combination, explaining up to 92% of total variance. Diversity decays exponentially with cell elongation and displays a log-normal dependence on cell volume, peaking for compact, intermediate-volume cells. 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.

Global Change Biology, 2018

Rapid evolution in response to environmental change will likely be a driving force determining th... more Rapid evolution in response to environmental change will likely be a driving force determining the distribution of species across the biosphere in coming decades. This is especially true of microorganisms, many of which may evolve in step with warming, including phytoplankton, the diverse photosynthetic microbes forming the foundation of most aquatic food webs. Here we tested the capacity of a globally important, model marine diatom Thalassiosira pseudonana, for rapid evolution in response to temperature. Selection at 16 and 31°C for 350 generations led to significant divergence in several temperature response traits, demonstrating local adaptation and the existence of trade-offs associated with adaptation to different temperatures. In contrast, competitive ability for nitrogen (commonly limiting in marine systems), measured after 450 generations of temperature selection, did not diverge in a systematic way between temperatures. This study shows how rapid thermal adaptation affects key temperature and nutrient traits and, thus, a population's long-term physiological, ecological, and biogeographic response to climate change.

Rapid evolution in response to environmental change will likely be a driving force determining th... more 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 °C for 350-450 generations led to significant divergence in several traits associated with T. pseudonana's thermal reaction norm (TRN) for per-capita population growth, as well as in its competitive ability for nitrogen (commonly limiting in marine systems). Of...

Aquatic Ecology, 2017

Rising lake temperatures and changing nutrient inputs are believed to favour the spread of a toxi... more Rising lake temperatures and changing nutrient inputs are believed to favour the spread of a toxic invasive cyanobacterium, Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju, in temperate lakes. However, most evidence for these hypotheses is observational or based on physiological measurements in monocultures. We lack clear experimental evidence relating temperature and nutrients to the competitive success of C. raciborskii. To address this, we performed a 2 9 2 factorial laboratory experiment to study the dynamics of mixed phytoplankton communities subjected to different levels of temperature and phosphorus over 51 days. We allowed C. raciborskii to compete with ten different species from major taxonomic groups (diatoms, green algae, cryptophytes, and cyanobacteria) typical of temperate lakes, under low and high summer temperatures (25 and 30°C) at two levels of phosphorus supply (1 and 25 lmol L-1). Cylindrospermopsis raciborskii dominated the communities and strongly decreased diversity under low-phosphorus conditions, consistent with the hypothesis that it is a good phosphorus competitor. In contrast, it remained extremely rare in high-phosphorus conditions, where fast-growing green algae dominated. Surprisingly, temperature played a negligible role in influencing community composition, suggesting that changes in summer temperature may not be important in determining C. raciborskii's spread.

Journal of Plankton Research, 2015

Marine phytoplankton are a taxonomically and functionally diverse group of organisms that are key... more Marine phytoplankton are a taxonomically and functionally diverse group of organisms that are key players in the most important biogeochemical cycles. Phytoplankton taxa show different resource utilization strategies (e.g. nutrient uptake rates and cellular allocation) and traits. Therefore, acknowledging this diversity is crucial to understanding how elemental cycles operate, including the origin and dynamics of elemental ratios. In this paper, we focus on trait-based models as tools to study the role of phytoplankton diversity in the stoichiometric phenomenology observed in the laboratory and in the open ocean. We offer a compilation of known empirical results on stoichiometry, and summarize how trait-based approaches have attempted to replicate these results. By contrasting the different ecological and evolutionary approaches available in the literature, we explore the strengths and limitations of the existing models. We thus try to identify existing gaps and challenges, and point to potential new directions that can be explored in order to fill these gaps. We aim to highlight the potential of including diversity explicitly in our modelling approaches, which can help us gain important knowledge about changes in local and global stoichiometric patterns.

Journal of Ecology, 2015

1. Phytoplankton are key players in the global carbon cycle, contributing about half of global pr... more 1. Phytoplankton are key players in the global carbon cycle, contributing about half of global primary productivity. Within the phytoplankton, functional groups (characterized by distinct traits) have impacts on other major biogeochemical cycles, such as nitrogen, phosphorus and silica. Changes in phytoplankton community structure, resulting from the unique environmental sensitivities of these groups, may significantly alter elemental cycling from local to global scales. 2. We review key traits that distinguish major phytoplankton functional groups, how they affect biogeochemistry and how the links between community structure and biogeochemical cycles are modelled. 3. Finally, we explore how global environmental change will affect phytoplankton communities, from the traits of individual species to the relative abundance of functional groups, and how that, in turn, may alter biogeochemical cycles. 4. Synthesis. We can increase our mechanistic understanding of the links between the community structure of primary producers and biogeochemistry by focusing on traits determining functional group responses to the environment (response traits) and their biogeochemical functions (effect traits). Identifying trade-offs including allometric and phylogenetic constraints among traits will help parameterize predictive biogeochemical models, enhancing our ability to anticipate the consequences of global change.

Philosophical Transactions of the Royal Society B: Biological Sciences, 2020

Environments change, for both natural and anthropogenic reasons, which can threaten species persi... more Environments change, for both natural and anthropogenic reasons, which can threaten species persistence. Evolutionary adaptation is a potentially powerful mechanism to allow species to persist in these changing environments. To determine the conditions under which adaptation will prevent extinction (evolutionary rescue), classic quantitative genetics models have assumed a constantly changing environment. They predict that species traits will track a moving environmental optimum with a lag that approaches a constant. If fitness is negative at this lag, the species will go extinct. There have been many elaborations of these models incorporating increased genetic realism. Here, we review and explore the consequences of four ecological complications: non-quadratic fitness functions, interacting density- and trait-dependence, species interactions and fundamental limits to adaptation. We show that non-quadratic fitness functions can result in evolutionary tipping points and existential cr...