Biology subjects

Narwani, A.

Publications and source records attributed to Narwani, A..

7 recordsLinked to original sources

bioRxiv2026

Divergent transcriptional responses of conserved cellular machinery to warming and phosphorus limitation in freshwater phytoplankton

Lakes are simultaneously warming and becoming phosphorus limited, but whether phytoplankton taxa of the same phylum respond through similar molecular mechanisms remains unclear, challenging a common assumption underlying predictions of ecological responses to environmental change. We cultured four freshwater phytoplankton species, including two diatoms (Fragilaria crotonensis and Nitzschia palea) and two cyanobacteria (Microcystis aeruginosa and Synechococcus sp.), across factorial gradients of temperature (20, 24 and 28 {degrees}C) and phosphorus (P) limitation, and characterized gene expression using RNA-seq, differential expression analysis and signed gene set enrichment. We generated predictions for expected responses for categories of gene functions derived from the growth rate (GRH) and temperature-dependent physiology hypotheses (TDPH). Warming and P limitation engaged largely the predicted functional categories in all species, however the direction of the response was not conserved, even within phyla--the two cyanobacteria regulated photosynthesis, ribosomal and chaperone genes in opposite directions. Ribosome- and translation-related genes gave the strongest warming response and, in N. palea, reversed direction within the species, increasing between 20 and 24 {degrees}C and decreasing between 24 and 28 {degrees}C, below the strain's thermal optimum estimated under moderate P limitation. Ribosomal allocation thus supported each hypothesis in different species and temperature ranges and was not predicted by thermal position alone. Where the interaction effects could be tested, P limitation rarely recruited novel pathways but modified existing warming responses, suppressing them in F. crotonensis and amplifying and redirecting them in M. aeruginosa. Molecular responses to combined drivers therefore diverge among related taxa, cautioning against aggregating species into functional groups when forecasting phytoplankton responses to global change.

molecular biology↗

bioRxiv2026

Rapid shallow-water saturation and deep-water expansion of an invasive freshwater ecosystem engineer in a deep European lake

Quagga mussels (Dreissena rostriformis bugensis) are ecosystem engineers that can alter nutrient cycling, benthic-pelagic coupling, and food-web structure in deep lakes. Although their invasion trajectories are well documented in the Laurentian Great Lakes in North America, depth-specific population dynamics remain poorly resolved in recently invaded European perialpine lakes. We analyzed five annual lake-wide surveys (2021-2025) from 54 stations spanning 2.4-253 m depth in Lake Constance to quantify changes in quagga mussel density, biomass, and shell-length distribution. Contrary to expectations of lake-wide exponential growth, shallow-water populations (< 20 m) showed no significant increase during the study period and appear to have reached carrying capacity before monitoring began. In contrast, densities increased monotonically at intermediate depths (40-125 m), indicating ongoing expansion into deeper strata. Mean shell length declined with depth, and size distributions in shallow waters shifted toward larger individuals, consistent with a transition from active recruitment to somatic growth of established mussels. Compared with the Laurentian Great Lakes, Lake Constance already has substantially higher shallow-water biomass, whereas deeper invasion trajectories are broadly similar. These results show that quagga mussel invasion in deep European lakes can combine rapid littoral saturation with slower profundal expansion, complicating direct transfer of predictions from the Great Lakes. Continued depth-stratified monitoring will be essential for anticipating future ecosystem effects in perialpine lakes.

ecology↗

bioRxiv2026

Pareto fronts reveal constraints on the evolution of niche-determining traits in phytoplankton

Trade-offs are central to biodiversity because they prevent the emergence of dominant phenotypes by limiting the simultaneous optimization of multiple fitness components. Yet trade-offs are often difficult to detect empirically when variation in overall performance produces positive correlations that mask underlying constraints. Here we use Pareto fronts--boundaries that capture optimal trade-off solutions--to test for evolutionary constraints on niche-determining traits in phytoplankton, including minimum nutrient requirements, thermal breadth, salt tolerance, and population growth rates. Using experimentally evolved Chlamydomonas reinhardtii populations subjected to nutrient and salt stress, we detected widespread Pareto fronts limiting the joint optimization of growth rate and niche-determining traits, thereby restricting the emergence of multivariate stress tolerance. Importantly, Pareto fronts revealed trade-offs even when underlying trait correlations were positive. We found that the structure of trait covariation behind Pareto fronts strongly predicted evolutionary outcomes: populations moved toward Pareto-optimal phenotypes primarily when trait correlations were neutral or positive, whereas negative trait correlations were associated with limited evolutionary optimization. Extending this framework across phytoplankton diversity, we compiled niche-determining traits for 299 phytoplankton taxa. At a macroevolutionary scale, we detected significant Pareto fronts constraining the evolution of niche-determining traits in phytoplankton. These fronts, however, did not always recapitulate the structure of trade-offs evident among C. reinhardtii populations, suggesting that forces that dictate microevolutionary outcomes, such as genetic correlations, can be resolved across macroevolutionary time. Together, our results highlight that evolutionary trajectories may differ across scales, but that fundamental limits on multivariate trait optimization persist across phytoplankton. Significance StatementTrade-offs among biological traits are central to evolutionary theory but often prove difficult to detect empirically. Here, we apply Pareto fronts--a framework borrowed from economics and engineering--to detect and reveal trade-offs among key niche-determining traits in phytoplankton. By combining experimental evolution in the laboratory with a synthesis of ecological traits across 299 taxa, we demonstrate widespread limits on the simultaneous optimization of growth rate, nutrient competition, salt tolerance, and thermal breadth. Importantly, Pareto fronts reveal trade-offs even when conventional correlation-based approaches fail, uncovering evolutionary constraints that remain hidden in trait correlations. These results show that trade-offs shape phenotypic variation across both micro- and macroevolutionary scales and impose fundamental limits on phytoplankton responses to multiple environmental stressors.

evolutionary biology↗

bioRxiv2025

Hunting for extremophiles: a systematic screening of freshwater microalgae for tolerance to high pH and high alkalinity cultivation

Microalgae hold the potential to supply sustainable food, fuel, plastics, and chemicals at commercial scales. Cultivating microalgae at extreme pH (>10) and high alkalinity provides multiple benefits including 1) reducing the risk of contamination by undesired organisms and 2) enabling direct air capture of CO2, which expands the land area suitable for algae farming compared to using CO2 point sources alone. However, we currently have a limited understanding of which algal taxa can grow under these conditions. Therefore, we conducted a high-throughput screening of 49 freshwater microalgae strains, comprising 40 species, for their ability to grow in moderate (pH 8.5, 25 mM alkalinity), high (pH 10, 75 mM alkalinity), and extreme (pH 10, 150 mM alkalinity) cultivation environments. Our results show that moderate alkalinity tends to significantly increase algae growth (including potentially harmful strains). However, higher levels inhibit all but a small subset of green algae and cyanobacteria. Effects of salinity and alkalinity differed, indicating they are broadly decoupled. Our results identify new industrially relevant alkaline-tolerant strains, show that algae isolated from "normal" ecosystems can be extremophilic, and suggest that future bioprospecting efforts for alkaline-tolerant algae adapted to local climatic conditions could yield additional productivity gains for the algae industry. SynopsisWe tested if 49 distinct microalgae strains could grow in high pH environments and found new and productive alkaline-tolerant strains Abstract/TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/676395v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@63d59dorg.highwire.dtl.DTLVardef@5d597eorg.highwire.dtl.DTLVardef@9e9be7org.highwire.dtl.DTLVardef@10d9160_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

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↗

bioRxiv2024

Botryococcus braunii reduces algal grazing losses to Daphnia and Poterioochromonas through both chemical and physical interference

Crop protection from algal grazers is a key area of concern, as grazing zooplankton and flagellates can decimate algal crops and impede economic viability of cultivation for biofuels and bioproducts. Inhibition of grazing by chemical and physical interference is one promising solution; however, there have been few empirical tests of this approach that use defense traits innate to algal crop species. Here we conduct an experiment to test whether the hydrocarbon excreting alga Botryococcus braunii can mitigate losses to grazing by two distinct grazers, Daphnia magna and Poterioochromonas malhamensis, due to both chemical inhibition and physical interference linked to large/inedible colonies. We show that chemical and physical defenses interactively reduce the total effect of grazing, thus significantly increasing the biomass of cultures of B. braunii and Nannochloropsis limnetica when either grazer is present. Specifically, B. braunii filtrate alone inhibits grazing and thus weakens top-down control of N. limnetica growth rates and final biomass by both grazers; B. braunii colonies alone also inhibit biomass losses; and the combination of filtrate and B. braunii colonies reveals an interactive effect of both chemical and physical defenses on grazing. Our study demonstrates how community engineering can identify synergies arising from algal cocultivation (e.g., by using industrially relevant strains for crop protection). Such ecological discoveries may help to reduce the costs of large-scale deployment of algal cultivation for sustainable foods, fuels, bioproducts (e.g., bioplastics), and carbon capture.

ecology↗

bioRxiv2019

The evolution of competitive ability for essential resources

Competition for limiting resources is among the most fundamental ecological interactions and has long been considered a key driver of species coexistence and biodiversity. Species minimum resource requirements, their R*s, are key traits that link individual physiological demands to the outcome of competition. However, a major question remains unanswered - to what extent are species competitive traits able to evolve in response to resource limitation? To address this knowledge gap, we performed an evolution experiment in which we exposed Chlamydomonas reinhardtii for approximately 285 generations to seven environments in chemostats which differed in resource supply ratios (including nitrogen, phosphorus and light limitation) and salt stress. We then grew the ancestors and descendants in common garden and quantified their competitive abilities for essential resources. We investigated constraints on trait evolution by testing whether changes in resource requirements for different resources were correlated. Competitive abilities for phosphorus improved in all populations, while competitive abilities for nitrogen and light increased in some populations and decreased in others. In contrast to the common assumption that there are trade-offs between competitive abilities for different resources, we found that improvements in competitive ability for a resource came at no detectable cost. Instead, improvements in competitive ability for multiple resources were either positively correlated or not significantly correlated. Using resource competition theory, we then demonstrated that rapid adaptation in competitive traits altered the predicted outcomes of competition. These results highlight the need to incorporate contemporary evolutionary change into predictions of competitive community dynamics over environmental gradients.

evolutionary biology↗