Metabolic-scale gene activation screens identify SLCO2B1 as a heme transporter that enhances cellular iron availability.

Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular players of iron utilization under iron restriction are incompletely understood. To address this, we performed metabolism-focused CRISPRa gain-of-function screens, which revealed metabolic limitations under stress conditions. Iron restriction screens identified not only expected members of iron utilization pathways but also SLCO2B1, a poorly characterized membrane carrier. SLCO2B1 expression is sufficient to increase intracellular iron, bypass the essentiality of the transferrin receptor, and enable proliferation under iron restriction. Mechanistically, SLCO2B1 mediates heme analog import in cellular assays. Heme uptake by SLCO2B1 provides sufficient iron for proliferation through heme oxygenases. Notably, SLCO2B1 is predominantly expressed in microglia in the brain, and primary Slco2b1-/- mouse microglia exhibit strong defects in heme analog import. Altogether, our work identifies SLCO2B1 as a microglia-enriched plasma membrane heme importer and provides a genetic platform to identify metabolic limitations under stress conditions.

Metabolic Reprogramming and Longevity in Quiescence.

Since Jacques Monod's foundational work in the 1940s, investigators studying bacterial physiology have largely (but not exclusively) focused on the exponential phase of bacterial cultures, which is characterized by rapid growth and high biosynthesis activity in the presence of excess nutrients. However, this is not the predominant state of bacterial life. In nature, most bacteria experience nutrient limitation most of the time. In fact, investigators even prior to Monod had identified other aspects of bacterial growth, including what is now known as the stationary phase, when nutrients become limiting. This review will discuss how bacteria transition to growth arrest in response to nutrient limitation through changes in transcription, translation, and metabolism. We will then examine how these changes facilitate survival during potentially extended periods of nutrient limitation, with particular attention to the metabolic strategies that underpin bacterial longevity in this state.

Nitrogen and sulfur for phosphorus: Lipidome adaptation of anaerobic sulfate-reducing bacteria in phosphorus-deprived conditions.

Understanding how microbial lipidomes adapt to environmental and nutrient stress is crucial for comprehending microbial survival and functionality. Certain anaerobic bacteria can synthesize glycerolipids with ether/ester bonds, yet the complexities of their lipidome remodeling under varying physicochemical and nutritional conditions remain largely unexplored. In this study, we thoroughly examined the lipidome adaptations of Desulfatibacillum alkenivorans strain PF2803T, a mesophilic anaerobic sulfate-reducing bacterium known for its high proportions of alkylglycerol ether lipids in its membrane, under various cultivation conditions including temperature, pH, salinity, and ammonium and phosphorous concentrations. Employing an extensive analytical and computational lipidomic methodology, we identified an assemblage of nearly 400 distinct lipids, including a range of glycerol ether/ester lipids with various polar head groups. Information theory-based analysis revealed that temperature fluctuations and phosphate scarcity profoundly influenced the lipidome's composition, leading to an enhanced diversity and specificity of novel lipids. Notably, phosphorous limitation led to the biosynthesis of novel glucuronosylglycerols and sulfur-containing aminolipids, termed butyramide cysteine glycerols, featuring various ether/ester bonds. This suggests a novel adaptive strategy for anaerobic heterotrophs to thrive under phosphorus-depleted conditions, characterized by a diverse array of nitrogen- and sulfur-containing polar head groups, moving beyond a reliance on conventional nonphospholipid types.

A distinct, high-affinity, alkaline phosphatase facilitates occupation of P-depleted environments by marine picocyanobacteria.

Marine picocyanobacteria of the genera Prochlorococcus and Synechococcus, the two most abundant phototrophs on Earth, thrive in oligotrophic oceanic regions. While it is well known that specific lineages are exquisitely adapted to prevailing in situ light and temperature regimes, much less is known of the molecular machinery required to facilitate occupancy of these low-nutrient environments. Here, we describe a hitherto unknown alkaline phosphatase, Psip1, that has a substantially higher affinity for phosphomonoesters than other well-known phosphatases like PhoA, PhoX, or PhoD and is restricted to clade III Synechococcus and a subset of high light I-adapted Prochlorococcus strains, suggesting niche specificity. We demonstrate that Psip1 has undergone convergent evolution with PhoX, requiring both iron and calcium for activity and likely possessing identical key residues around the active site, despite generally very low sequence homology. Interrogation of metagenomes and transcriptomes from TARA oceans and an Atlantic Meridional transect shows that psip1 is abundant and highly expressed in picocyanobacterial populations from the Mediterranean Sea and north Atlantic gyre, regions well recognized to be phosphorus (P)-deplete. Together, this identifies psip1 as an important oligotrophy-specific gene for P recycling in these organisms. Furthermore, psip1 is not restricted to picocyanobacteria and is abundant and highly transcribed in some α-proteobacteria and eukaryotic algae, suggesting that such a high-affinity phosphatase is important across the microbial taxonomic world to occupy low-P environments.

Carbon starvation raises capacities in bacterial antibiotic resistance and viral auxiliary carbon metabolism in soils.

Organic carbon availability in soil is crucial for shaping microbial communities, yet, uncertainties persist concerning microbial adaptations to carbon levels and the ensuing ecological and evolutionary consequences. We investigated organic carbon metabolism, antibiotic resistance, and virus-host interactions in soils subjected to 40 y of chemical and organic fertilization that led to contrasting carbon availability: carbon-poor and carbon-rich soils, respectively. Carbon-poor soils drove the enrichment of putative genes involved in organic matter decomposition and exhibited specialization in utilizing complex organic compounds, reflecting scramble competition. This specialization confers a competitive advantage of microbial communities in carbon-poor soils but reduces their buffering capacity in terms of organic carbon metabolisms, making them more vulnerable to environmental fluctuations. Additionally, in carbon-poor soils, viral auxiliary metabolic genes linked to organic carbon metabolism increased host competitiveness and environmental adaptability through a strategy akin to "piggyback the winner." Furthermore, putative antibiotic resistance genes, particularly in low-abundance drug categories, were enriched in carbon-poor soils as an evolutionary consequence of chemical warfare (i.e., interference competition). This raises concerns about the potential dissemination of antibiotic resistance from conventional agriculture that relies on chemical-only fertilization. Consequently, carbon starvation resulting from long-term chemical-only fertilization increases microbial adaptations to competition, underscoring the importance of implementing sustainable agricultural practices to mitigate the emergence and spread of antimicrobial resistance and to increase soil carbon storage.

Toward a metabolic theory of catchments: Scaling of water and carbon fluxes with size.

Allometric scaling relations are widely used to link biological processes to body size in nature. Several studies have shown that such scaling laws hold also for natural ecosystems, including individual trees and forests, riverine metabolism, and river network organization. However, the derivation of scaling laws for catchment-scale water and carbon fluxes has not been achieved so far. Here, we focus on scaling relations of catchment green metabolism, defined as the set of ecohydrological and biogeochemical processes through which vegetation assemblages in catchments maintain their structure and react to the surrounding environment. By revising existing plant size-density relationships and integrating them across large-scale domains, we show that the ecohydrological fluxes occurring at the catchment scale are invariant with respect to the above-ground vegetation biomass per unit area of the basin, while they scale linearly with catchment size. We thus demonstrate that the sublinear scaling of plant metabolism results in an isometric scaling at catchment and regional scales. Deviations from such predictions are further shown to collapse onto a common distribution, thus incorporating natural fluctuations due to resource limitations into a generalized scaling theory. Results from scaling arguments are supported by hyperresolution ecohydrological simulations and remote sensing observations.

Post-Transcriptional Regulation of Rab7a in Lysosomal Positioning and Drug Resistance in Nutrient-Limited Cancer Cells.

Limited nutrient availability in the tumor microenvironment can cause the rewiring of signaling and metabolic networks to confer cancer cells with survival advantages. We show here that the limitation of glucose, glutamine and serum from the culture medium resulted in the survival of a population of cancer cells with high viability and capacity to form tumors in vivo. These cells also displayed a remarkable increase in the abundance and size of lysosomes. Moreover, lysosomes were located mainly in the perinuclear region in nutrient-limited cells; this translocation was mediated by a rapid post-transcriptional increase in the key endolysosomal trafficking protein Rab7a. The acidic lysosomes in nutrient-limited cells could trap weakly basic drugs such as doxorubicin, mediating resistance of the cells to the drug, which could be partially reversed with the lysosomal inhibitor bafilomycin A1. An in vivo chorioallantoic membrane (CAM) assay indicated a remarkable decrease in microtumor volume when nutrient-limited cells were treated with 5-Fluorouracil (5-FU) and bafilomycin A1 compared to cells treated with either agent alone. Overall, our data indicate the activation of complementary pathways with nutrient limitation that can enable cancer cells to survive, proliferate and acquire drug resistance.

Long-term, large-scale experiment reveals the effects of seed limitation, climate, and anthropogenic disturbance on restoration of plant communities in a biodiversity hotspot.

Ecological restoration is essential for maintaining biodiversity in the face of dynamic, global changes in climate, human land use, and disturbance regimes. Effective restoration requires understanding bottlenecks in plant community recovery that exist today, while recognizing that these bottlenecks may relate to complex histories of environmental change. Such understanding has been a challenge because few long-term, well-replicated experiments exist to decipher the demographic processes influencing recovery for numerous species against the backdrop of multiyear variation in climate and management. We address this challenge through a long-term and geographically expansive experiment in longleaf pine savannas, an imperiled ecosystem and biodiversity hotspot in the southeastern United States. Using 48 sites at three locations spanning 480 km, the 8-y experiment manipulated initial seed arrival for 24 herbaceous plant species and presence of competitors to evaluate the impacts of climate variability and management actions (e.g., prescribed burning) on plant establishment and persistence. Adding seeds increased plant establishment of many species. Cool and wet climatic conditions, low tree density, and reduced litter depth also promoted establishment. Once established, most species persisted for the duration of the 8-y experiment. Plant traits were most predictive when tightly coupled to the process of establishment. Our results illustrate how seed additions can restore plant diversity and how interannual climatic variation affects the dynamics of plant communities across a large region. The significant effects of temperature and precipitation inform how future climate may affect restoration and conservation via large-scale changes in the fundamental processes of establishment and persistence.

Functional analysis of regA paralog rlsD in Volvox carteri.

Volvox carteri is an excellent system for investigating the origins of cell differentiation because it possesses just two cell types, reproductive gonidia and motile somatic cells, which evolved relatively recently. The somatic phenotype depends on the regA gene, which represses cell growth and reproduction, preventing cells expressing it from growing large enough to become gonidia. regA encodes a putative transcription factor and was generated in an undifferentiated ancestor of V. carteri through duplication of a progenitor gene whose ortholog in V. carteri is named rlsD. Here we analyze the function of rlsD through knockdown, overexpression, and RNA-seq experiments, to gain clues into the function of a member of an understudied putative transcription factor family and to obtain insight into the origins of cell differentiation in the volvocine algae. rlsD knockdown was lethal, while rlsD overexpression dramatically reduced gonidial growth. rlsD overexpression led to differential expression of approximately one-fourth of the genome, with repressed genes biased for those typically overexpressed in gonidia relative to somatic cells, and upregulated genes biased toward expression in soma, where regA expression is high. Notably, rlsD overexpression affects accumulation of transcripts for genes/Pfam domains involved in ribosome biogenesis, photosynthetic light harvesting, and sulfate generation, functions related to organismal growth, and responses to resource availability. We also found that in the wild type, rlsD expression is induced by light deprivation. These findings are consistent with the idea that cell differentiation in V. carteri evolved when a resource-responsive, growth-regulating gene was amplified, and a resulting gene duplicate was co-opted to repress growth in a constitutive, spatial context.

Severity of Airflow Obstruction Based on FEV1/FVC vs FEV1% of Predicted in the General US Population.

RATIONALE: According to GOLD, the ratio of FEV1/FVC is used to confirm airflow obstruction in COPD diagnosis, whereas FEV1% of predicted (FEV1%pred) is used for severity grading. STaging of Airflow obstruction by the FEV1/FVC Ratio (STAR) and its prediction of adverse outcomes has not been evaluated in general populations. OBJECTIVE: To compare the STAR (FEV1/FVC) versus GOLD (FEV1%pred) classification for the severity of airflow limitation in terms of exertional breathlessness and mortality in the general US population. METHODS: Severity stages according to STAR and GOLD were applied to the multi-ethnic National Health and Nutrition Examination Survey (NHANES) 2007-2012 survey including ages 18-80 years, using post-bronchodilatory FEV1/FVC<0.70 to define airflow obstruction in both staging systems. Prevalence of severity stages STAR 1-4 and GOLD 1-4 was calculated and associations with breathlessness and mortality were analyzed by multinomial logistic regression and Cox regression, respectively. RESULTS: STAR versus GOLD severity staging of airflow obstruction showed similar associations with breathlessness and all-cause mortality, regardless of ethnicity/race. In those with airflow obstruction, the correlation between the two classification systems was 0.461 (p<0.001). STAR reclassified 59% of GOLD stage 2 as having mild airflow obstruction (STAR 1). STAR 1 was more clearly differentiated from the non-obstructive compared to GOLD stage 1 in terms of both breathlessness and mortality. CONCLUSIONS: FEV1/FVC and FEV1%pred as measures of severity of airflow limitation show similar prediction of breathlessness and mortality in the adult US population across ethnicity groups. However, stage 1 differed more clearly from non-obstructive based on FEV1/FVC than FEV1%pred. This article is open access and distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).

Trade-offs of lipid remodeling in a marine predator-prey interaction in response to phosphorus limitation.

Phosphorus (P) is a key nutrient limiting bacterial growth and primary production in the oceans. Unsurprisingly, marine microbes have evolved sophisticated strategies to adapt to P limitation, one of which involves the remodeling of membrane lipids by replacing phospholipids with non-P-containing surrogate lipids. This strategy is adopted by both cosmopolitan marine phytoplankton and heterotrophic bacteria and serves to reduce the cellular P quota. However, little, if anything, is known of the biological consequences of lipid remodeling. Here, using the marine bacterium Phaeobacter sp. MED193 and the ciliate Uronema marinum as a model, we sought to assess the effect of remodeling on bacteria-protist interactions. We discovered an important trade-off between either escape from ingestion or resistance to digestion. Thus, Phaeobacter grown under P-replete conditions was readily ingested by Uronema, but not easily digested, supporting only limited predator growth. In contrast, following membrane lipid remodeling in response to P depletion, Phaeobacter was less likely to be captured by Uronema, thanks to the reduced expression of mannosylated glycoconjugates. However, once ingested, membrane-remodeled cells were unable to prevent phagosome acidification, became more susceptible to digestion, and, as such, allowed rapid growth of the ciliate predator. This trade-off between adapting to a P-limited environment and susceptibility to protist grazing suggests the more efficient removal of low-P prey that potentially has important implications for the functioning of the marine microbial food web in terms of trophic energy transfer and nutrient export efficiency.

Circulating biomarkers of airflow limitation across the life span.

BACKGROUND: Airflow limitation is a hallmark of chronic obstructive pulmonary disease, which can develop through different lung function trajectories across the life span. There is a need for longitudinal studies aimed at identifying circulating biomarkers of airflow limitation across different stages of life. OBJECTIVES: This study sought to identify a signature of serum proteins associated with airflow limitation and evaluate their relation to lung function longitudinally in adults and children. METHODS: This study used data from 3 adult cohorts (TESAOD [Tucson Epidemiological Study of Airway Obstructive Disease], SAPALDIA [Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults], LSC [Lovelace Smoker Cohort]) and 1 birth cohort (TCRS [Tucson Children's Respiratory Study]) (N = 1940). In TESAOD, among 46 circulating proteins, we identified those associated with FEV1/forced vital capacity (FVC) percent (%) predicted levels and generated a score based on the sum of their z-scores. Cross-sectional analyses were used to test the score for association with concomitant lung function. Longitudinal analyses were used to test the score for association with subsequent lung function growth in childhood and decline in adult life. RESULTS: After false discovery rate adjustment, serum levels of 5 proteins (HP, carcinoembryonic antigen, ICAM1, CRP, TIMP1) were associated with percent predicted levels of FEV1/FVC and FEV1 in TESAOD. In cross-sectional multivariate analyses the 5-biomarker score was associated with FEV1 % predicted in all adult cohorts (meta-analyzed FEV1 decrease for 1-SD score increase: -2.9%; 95% CI: -3.9%, -1.9%; P = 2.4 × 10-16). In multivariate longitudinal analyses, the biomarker score at 6 years of age was inversely associated with FEV1 and FEV1/FVC levels attained by young adult life (P = .02 and .005, respectively). In adults, persistently high levels of the biomarker score were associated with subsequent accelerated decline of FEV1 and FEV1/FVC (P = .01 and .001). CONCLUSIONS: A signature of 5 circulating biomarkers of airflow limitation was associated with both impaired lung function growth in childhood and accelerated lung function decline in adult life, indicating that these proteins may be involved in multiple lung function trajectories leading to chronic obstructive pulmonary disease.

How Nutrients Mediate the Impacts of Global Change on Locust Outbreaks.

Locusts are grasshoppers that can migrate en masse and devastate food security. Plant nutrient content is a key variable influencing population dynamics, but the relationship is not straightforward. For an herbivore, plant quality depends not only on the balance of nutrients and antinutrients in plant tissues, which is influenced by land use and climate change, but also on the nutritional state and demands of the herbivore, as well as its capacity to extract nutrients from host plants. In contrast to the concept of a positive relationship between nitrogen or protein concentration and herbivore performance, a five-decade review of lab and field studies indicates that equating plant N to plant quality is misleading because grasshoppers respond negatively or neutrally to increasing plant N just as often as they respond positively. For locusts specifically, low-N environments are actually beneficial because they supply high energy rates that support migration. Therefore, intensive land use, such as continuous grazing or cropping, and elevated ambient CO2 levels that decrease the protein:carbohydrate ratios of plants are predicted to broadly promote locust outbreaks.

The plant root economics space in relation to nutrient limitation in Eurasian herbaceous plant communities.

Plant species occupy distinct niches along a nitrogen-to-phosphorus (N:P) gradient, yet there is no general framework for belowground nutrient acquisition traits in relation to N or P limitation. We retrieved several belowground traits from databases, placed them in the "root economics space" framework, and linked these to a dataset of 991 plots in Eurasian herbaceous plant communities, containing plant species composition, aboveground community biomass and tissue N and P concentrations. Our results support that under increasing N:P ratio, belowground nutrient acquisition strategies shift from "fast" to "slow" and from "do-it-yourself" to "outsourcing", with alternative "do-it-yourself" to "outsourcing" strategies at both ends of the spectrum. Species' mycorrhizal capacity patterns conflicted with root economics space predictions based on root diameter, suggesting evolutionary development of alternative strategies under P limitation. Further insight into belowground strategies along nutrient stoichiometry is crucial for understanding the high abundance of threatened plant species under P limitation.

A grazer's niche edge is associated with increasing diet diversity and poor population performance.

The core-periphery hypothesis predicts niche cores should be associated with greater survivorship, reproductive output and population performance rates than marginal habitats at niche edges. However, there is very little empirical evidence of whether niche centrality influences population trends in animals. Using the Cape mountain zebra (Equus zebra zebra) as a model system, we evaluated whether niche centrality is associated with population trends, resource availability and diet across a core-periphery gradient. Population growth rates and density progressively declined towards niche peripheries. Niche peripheries were resource-poor and Cape mountain zebra consumed more phylogenetically diverse diets dominated by non-grass families. In core habitats they consumed grass-rich diets and female reproductive success was higher. This combination of spatial niche modelling and functional ecology provides a novel evaluation of how bottom-up resource limitation can shape species distributions, population resilience and range change and can guide conservation management.

Interactions between temperature and nutrients determine the population dynamics of primary producers.

Global change is rapidly and fundamentally altering many of the processes regulating the flux of energy throughout ecosystems, and although researchers now understand the effect of temperature on key rates (such as aquatic primary productivity), the theoretical foundation needed to generate forecasts of biomass dynamics and extinction risk remains underdeveloped. We develop new theory that describes the interconnected effects of nutrients and temperature on phytoplankton populations and show that the thermal response of equilibrium biomass (i.e. carrying capacity) always peaks at a lower temperature than for productivity (i.e. growth rate). This mismatch is driven by differences in the thermal responses of growth, death, and per-capita impact on the nutrient pool, making our results highly general and applicable to widely used population models beyond phytoplankton. We further show that non-equilibrium dynamics depend on the pace of environmental change relative to underlying vital rates and that populations respond to variable environments differently at high versus low temperatures due to thermal asymmetries.

Responses of intraspecific metabolic scaling to temperature and activity differ between water- and air-breathing ectothermic vertebrates.

Metabolism underpins all life-sustaining processes and varies profoundly with body size, temperature and locomotor activity. A current theory explains some of the size-dependence of metabolic rate (its mass exponent, b) through changes in metabolic level (L). We propose two predictive advances that: (a) combine the above theory with the evolved avoidance of oxygen limitation in water-breathers experiencing warming, and (b) quantify the overall magnitude of combined temperatures and degrees of locomotion on metabolic scaling across air- and water-breathers. We use intraspecific metabolic scaling responses to temperature (523 regressions) and activity (281 regressions) in diverse ectothermic vertebrates (fish, reptiles and amphibians) to show that b decreases with temperature-increased L in water-breathers, supporting surface area-related avoidance of oxygen limitation, whereas b increases with activity-increased L in air-breathers, following volume-related influences. This new theoretical integration quantitatively incorporates different influences (warming, locomotion) and respiration modes (aquatic, terrestrial) on animal energetics.

Understanding different dominance patterns in western Amazonian forests.

Dominance of neotropical tree communities by a few species is widely documented, but dominant trees show a variety of distributional patterns still poorly understood. Here, we used 503 forest inventory plots (93,719 individuals ≥2.5 cm diameter, 2609 species) to explore the relationships between local abundance, regional frequency and spatial aggregation of dominant species in four main habitat types in western Amazonia. Although the abundance-occupancy relationship is positive for the full dataset, we found that among dominant Amazonian tree species, there is a strong negative relationship between local abundance and regional frequency and/or spatial aggregation across habitat types. Our findings suggest an ecological trade-off whereby dominant species can be locally abundant (local dominants) or regionally widespread (widespread dominants), but rarely both (oligarchs). Given the importance of dominant species as drivers of diversity and ecosystem functioning, unravelling different dominance patterns is a research priority to direct conservation efforts in Amazonian forests.

Phosphate Limitation Responses in Marine Green Algae Are Linked to Reprogramming of the tRNA Epitranscriptome and Codon Usage Bias.

Marine algae are central to global carbon fixation, and their productivity is dictated largely by resource availability. Reduced nutrient availability is predicted for vast oceanic regions as an outcome of climate change; however, there is much to learn regarding response mechanisms of the tiny picoplankton that thrive in these environments, especially eukaryotic phytoplankton. Here, we investigate responses of the picoeukaryote Micromonas commoda, a green alga found throughout subtropical and tropical oceans. Under shifting phosphate availability scenarios, transcriptomic analyses revealed altered expression of transfer RNA modification enzymes and biased codon usage of transcripts more abundant during phosphate-limiting versus phosphate-replete conditions, consistent with the role of transfer RNA modifications in regulating codon recognition. To associate the observed shift in the expression of the transfer RNA modification enzyme complement with the transfer RNAs encoded by M. commoda, we also determined the transfer RNA repertoire of this alga revealing potential targets of the modification enzymes. Codon usage bias was particularly pronounced in transcripts encoding proteins with direct roles in managing phosphate limitation and photosystem-associated proteins that have ill-characterized putative functions in "light stress." The observed codon usage bias corresponds to a proposed stress response mechanism in which the interplay between stress-induced changes in transfer RNA modifications and skewed codon usage in certain essential response genes drives preferential translation of the encoded proteins. Collectively, we expose a potential underlying mechanism for achieving growth under enhanced nutrient limitation that extends beyond the catalog of up- or downregulated protein-encoding genes to the cell biological controls that underpin acclimation to changing environmental conditions.

Anisogamy Does Not Always Promote the Evolution of Mating Competition Traits in Males.

AbstractAnisogamy has evolved in most sexually reproducing multicellular organisms allowing the definition of male and female sexes, producing small and large gametes. Anisogamy, as the initial sexual dimorphism, is a good starting point to understand the evolution of further sexual dimorphisms. For instance, it is generally accepted that anisogamy sets the stage for more intense mating competition in males than in females. We argue that this idea stems from a restrictive assumption on the conditions under which anisogamy evolved in the first place: the absence of sperm limitation (assuming that all female gametes are fertilized). Here, we relax this assumption and present a model that considers the coevolution of gamete size with a mating competition trait, starting in a population without dimorphism. We vary gamete density to produce different scenarios of gamete limitation. We show that while at high gamete density the evolution of anisogamy always results in male investment in competition, gamete limitation at intermediate gamete densities allows for either females or males to invest more into mating competition. Our results thus suggest that anisogamy does not always promote mating competition among males. The conditions under which anisogamy evolves matter, as does the competition trait.