A model of time-dependent macromolecular and elemental composition of phytoplankton.

Phytoplankton Chl:C:N:P ratios are important from both an ecological and a biogeochemical perspective. We show that these elemental ratios can be represented by a phytoplankton physiological model of low complexity that includes major cellular macromolecular pools. In particular, our model resolves time-dependent intracellular pools of chlorophyll, proteins, nucleic acids, carbohydrates/lipids, and N and P storage. Batch culture data for two diatom and two prasinophyte species are used to constrain parameters that represent specific allocation traits and strategies. A key novelty is the simultaneous estimation of physiological parameters for two phytoplankton groups of such different sizes. The number of free parameters is reduced by assuming (i) allometric scaling for maximum uptake rates, (ii) shared half-saturation constants for synthesis of functional macromolecules, (iii) shared exudation rates of functional macromolecules across the species. The rationale behind this assumption is that across the different species, the same or similar processes, enzymes, and metabolites play a role in key physiological processes. For the turnover numbers of macromolecular synthesis and storage exudation rates, differences between diatoms and prasinophytes need to be taken into account to obtain a good fit. Our model fits suggest that the parameters related to storage dynamics dominate the differences in the C:N:P ratios between the different phytoplankton groups. Since descriptions of storage dynamics are still incomplete and imprecise, predictions of C:N:P ratios by phytoplankton models likely have a large uncertainty.

Common environmental stress responses in a model marine diatom.

Marine planktonic diatoms are among the most important contributors to phytoplankton blooms and marine net primary production. Their ecological success has been attributed to their ability to rapidly respond to changing environmental conditions. Here, we report common molecular mechanisms used by the model marine diatom Thalassiosira pseudonana to respond to 10 diverse environmental stressors using RNA-Seq analysis. We identify a specific subset of 1076 genes that are differentially expressed in response to stressors that induce an imbalance between energy or resource supply and metabolic capacity, which we termed the diatom environmental stress response (d-ESR). The d-ESR is primarily composed of genes that maintain proteome homeostasis and primary metabolism. Photosynthesis is strongly regulated in response to environmental stressors but chloroplast-encoded genes were predominantly upregulated while the nuclear-encoded genes were mostly downregulated in response to low light and high temperature. In aggregate, these results provide insight into the molecular mechanisms used by diatoms to respond to a range of environmental perturbations and the unique role of the chloroplast in managing environmental stress in diatoms. This study facilitates our understanding of the molecular mechanisms underpinning the ecological success of diatoms in the ocean.

Elemental stoichiometry of the key calcifying marine phytoplankton Emiliania huxleyi under ocean climate change: A meta-analysis.

The elemental composition of marine microorganisms (their C:N:P ratio, or stoichiometry) is central to understanding the biotic and biogeochemical processes underlying key marine ecosystem functions. Phytoplankton C:N:P is species specific and flexible to changing environmental conditions. However, bulk or fixed phytoplankton stoichiometry is usually assumed in biogeochemical and ecological models because more realistic, environmentally responsive C:N:P ratios have yet to be defined for key functional groups. Here, a comprehensive meta-analysis of experimental laboratory data reveals the variable C:N:P stoichiometry of Emiliania huxleyi, a globally significant calcifying phytoplankton species. Mean C:N:P of E. huxleyi is 124C:16N:1P under control conditions (i.e. growth not limited by one or more environmental stressors) and shows a range of responses to changes in nutrient and light availability, temperature and pCO2 . Macronutrient limitation caused strong shifts in stoichiometry, increasing N:P and C:P under P deficiency (by 305% and 493% respectively) and doubling C:N under N deficiency. Responses to light, temperature and pCO2 were mixed but typically shifted cellular elemental content and C:N:P stoichiometry by ca. 30% or less. Besides these independent effects, the interactive effects of multiple environmental changes on E. huxleyi stoichiometry under future ocean conditions could be additive, synergistic or antagonistic. To synthesise our meta-analysis results, we explored how the cellular elemental content and C:N:P stoichiometry of E. huxleyi may respond to two hypothetical future ocean scenarios (increased temperature, irradiance and pCO2 combined with either N deficiency or P deficiency) if an additive effect is assumed. Both future scenarios indicate decreased calcification (which is predominantly sensitive to elevated pCO2 ), increased C:N, and up to fourfold shifts in C:P and N:P. Our results strongly suggest that climate change will significantly alter the role of E. huxleyi (and potentially other calcifying phytoplankton species) in marine biogeochemical processes.

Conservation and architecture of housekeeping genes in the model marine diatom Thalassiosira pseudonana.

Housekeeping genes (HKGs) are constitutively expressed with low variation across tissues/conditions. They are thought to be highly conserved and fundamental to cellular maintenance, with distinctive genomic features. Here, we identify 1505 HKGs in the unicellular marine diatom Thalassiosira pseudonana based on an RNA-seq analysis of 232 samples taken under 12 experimental conditions over 0-72 h. We identify promising internal reference genes (IRGs) for T. pseudonana from the most stably expressed HKGs. A comparative analysis indicates < 18% of HKGs in T. pseudonana have orthologs in other eukaryotes, including other diatom species. Contrary to work on human tissues, T. pseudonana HKGs are longer than non-HKGs, due to elongated introns. More ancient HKGs tend to be shorter than more recent HKGs, and expression levels of HKGs decrease more rapidly with gene length relative to non-HKGs. Our results indicate that HKGs are highly variable across the tree of life and thus unlikely to be universally fundamental for cellular maintenance. We hypothesize that the distinct genomic features of HKGs of T. pseudonana may be a consequence of selection pressures associated with high expression and low variance across conditions.

Anthropogenic climate change impacts on copepod trait biogeography.

Copepods are among the most abundant marine metazoans and form a key link between marine primary producers, higher trophic levels, and carbon sequestration pathways. Climate change is projected to change surface ocean temperature by up to 4°C in the North Atlantic with many associated changes including slowing of the overturning circulation, areas of regional freshening, and increased salinity and reductions in nutrients available in the euphotic zone over the next century. These changes will lead to a restructuring of phytoplankton and zooplankton communities with cascading effects throughout the food web. Here we employ observations of copepods, projected changes in ocean climate, and species distribution models to show how climate change may affect the distribution of copepod species in the North Atlantic. On average species move northeast at a rate of 14.1 km decade-1 . Species turnover in copepod communities will range from 5% to 75% with the highest turnover rates concentrated in regions of pronounced temperature increase and decrease. The changes in species range vary according to copepod traits with the largest effects found to occur in the cooling, freshening area in the subpolar North Atlantic south of Greenland and in an area of significant warming along the Scotian shelf. Large diapausing copepods (>2.5 mm) which are higher in lipids and a crucial food source for whales, may have an advantage in the cooling waters due to their life-history strategy that facilitates their survival in the arctic environment. Carnivorous copepods show a basin wide increase in species richness and show significant habitat area increases when their distribution moves poleward while herbivores see significant habitat area losses. The trait-specific effects highlight the complex consequences of climate change for the marine food web.

Dynamic Photophysiological Stress Response of a Model Diatom to Ten Environmental Stresses.

Stressful environmental conditions can induce many different acclimation mechanisms in marine phytoplankton, resulting in a range of changes in their photophysiology. Here we characterize the common photophysiological stress response of the model diatom Thalassiosira pseudonana to ten environmental stressors and identify diagnostic responses to particular stressors. We quantify the magnitude and temporal trajectory of physiological parameters including the functional absorption cross-section of PSII (σPSII ), quantum efficiency of PSII, non-photochemical quenching (NPQ), cell volume, Chl a, and carotenoid (Car) content in response to nutrient starvation (nitrogen (N), phosphorus (P), silicon (Si), and iron (Fe)), changes in temperature, irradiance, pH, and reactive oxygen species (ROS) over 5 time points (0, 2, 6, 24, 72 h). We find changes in conditions: temperature, irradiance, and ROS, often result in the most rapid changes in photophysiological parameters (<2 h), and in some cases are followed by recovery. In contrast, nutrient starvation (N, P, Si, Fe) often has slower (6-72 h) but ultimately larger magnitude effects on many photophysiological parameters. Diagnostic changes include large increases in cell volume under Si-starvation, very large increases in NPQ under P-starvation, and large decreases in the σPSII under high light. The ultimate goal of this analysis is to facilitate and enhance the interpretation of fluorescence data and our understanding of phytoplankton photophysiology from laboratory and field studies.

Photosynthetic adaptation to light availability shapes the ecological success of bloom-forming cyanobacterium Pseudanabaena to iron limitation.

The poorly understood filamentous cyanobacterium Pseudanabaena is commonly epiphytic on Microcystis colonies and their abundances are often highly correlated during blooms. The response and adaptation of Microcystis to iron limitation have been extensively studied, but the strategies Pseudanabaena uses to respond to iron limitation are largely unknown. Here, physiological responses to iron limitation were compared between one Pseudanabaena and two Microcystis strains grown under different light intensities. The results showed that low-intensity light exacerbated, but high-intensity light alleviated, the negative effect of iron limitation on Pseudanabaena growth relative to two Microcystis strains. It was found that robust light-harvesting and photosynthetic efficiency allowed adaptation of Pseudanabaena to low light availability relative to two Microcystis strains only during iron sufficiency. The results also indicated that a larger investment in the photosynthetic antenna probably contributed to light/iron co-limitation of Pseudanabaena relative to two Microcystis strains under both light and iron limitation. Furthermore, the lower antenna pigments/chlorophyll a ratio and photosynthetic efficiency, and higher nonphotochemical quenching and saturation irradiance provided Pseudanabaena photoadaptation and photoprotection advantages over the two Microcystis strains under the high-light condition. The lower investment in antenna pigments of Pseudanabaena than the two Microcystis strains under high-light intensity is likely an efficient strategy for both saving iron quotas and decreasing photosensitivity. Therefore, when compared with Microcystis, the high plasticity of antenna pigments, along with the excellent photoadaptation and photoprotection ability of Pseudanabaena, probably ensures its ecological success under iron limitation when light is sufficient.

The macromolecular composition of noncalcified marine macroalgae.

The macromolecular composition of macroalgae influences nutrient flow and food quality in aquatic ecosystems and the value of macroalgae species for human consumption, aquaculture, biofuels, and other applications. We used literature data (125 publications, 1,117 observations) and a hierarchal Bayesian statistical model to estimate the average macromolecular composition, protein, lipid, and carbohydrate of macroalgae as a whole and at the phylum level. Our focus was on marine, noncalcified macroalgae sampled from wild-grown populations in the field. We found that the median macromolecular composition is 9.98% protein, 2.7% lipid, 48.5% carbohydrate, and 31.8% ash as percent dry weight. We compared the median macromolecular content of macroalgae to microalgae and herbaceous plants and test for differences in macromolecular content across macroalgal phyla. Macroalgae were much more enriched in carbohydrate and minerals than the microalgae and lower in protein and lipid than many herbaceous plants. Rhodophyte macroalgae have significantly less lipid and more protein and the Ochrophyte macroalgae have significantly less protein than the average.

Anthropogenic climate change drives shift and shuffle in North Atlantic phytoplankton communities.

Anthropogenic climate change has shifted the biogeography and phenology of many terrestrial and marine species. Marine phytoplankton communities appear sensitive to climate change, yet understanding of how individual species may respond to anthropogenic climate change remains limited. Here, using historical environmental and phytoplankton observations, we characterize the realized ecological niches for 87 North Atlantic diatom and dinoflagellate taxa and project changes in species biogeography between mean historical (1951-2000) and future (2051-2100) ocean conditions. We find that the central positions of the core range of 74% of taxa shift poleward at a median rate of 12.9 km per decade (km⋅dec(-1)), and 90% of taxa shift eastward at a median rate of 42.7 km⋅dec(-1) The poleward shift is faster than previously reported for marine taxa, and the predominance of longitudinal shifts is driven by dynamic changes in multiple environmental drivers, rather than a strictly poleward, temperature-driven redistribution of ocean habitats. A century of climate change significantly shuffles community composition by a basin-wide median value of 16%, compared with seasonal variations of 46%. The North Atlantic phytoplankton community appears poised for marked shift and shuffle, which may have broad effects on food webs and biogeochemical cycles.

A prospective observational trial of fusion imaging in infrarenal aneurysms.

OBJECTIVE: Use of three-dimensional fusion has been shown to significantly reduce radiation exposure and contrast material use in complex (fenestrated and branched) endovascular aneurysm repair (EVAR). Cydar software (CYDAR Medical, Cambridge, United Kingdom) is a cloud-based technology that can provide imaging guidance by overlaying preoperative three-dimensional vessel anatomy from computed tomography scans onto live fluoroscopy images both in hybrid operating rooms and on mobile C-arms. The aim of this study was to determine whether radiation dose reduction would occur with the addition of fusion imaging to infrarenal repair in all imaging environments. METHODS: All patients who consented to involvement in the trial and who were treated with EVAR in our center from March 2016 until April 2017 were included. A teaching session about radiation protection and Cydar fusion software use was provided to all operators before the start of the fusion group enrollment. This group was compared with a retrospective cohort of patients treated in the same center from March 2015 to March 2016, after a dedicated program of radiation awareness and reduction was introduced. Ruptured aneurysms and complex EVAR were excluded. Preoperative and perioperative characteristics were recorded, including parameters of radiation dose, such as air kerma and dose-area product. Results were expressed in median and interquartile range. RESULTS: Forty-four patients were prospectively enrolled and compared with 21 retrospective control patients. No significant differences were found in comparing sex, body mass index, and age at repair. The median operation time (wire to wire) and fluoroscopy time were 90 (75-105) minutes and 30 (22-34) minutes, respectively, without significant differences between groups (P = .56 and P = .36). Dose-area product was nonsignificantly higher in the control group, 21.7 (8.9-85.9) Gy cm2, compared with the fusion group, 12.4 (7.5-23.4) Gy cm2 (P = .10). Air kerma product was significantly higher in the control group, 142 (61-541) mGy, compared with 82 (51-115) mGy in the fusion group (P = .03). The number of digital subtraction angiography runs was significantly lower in the fusion group (8 [6-11]) compared with the control group (10 [9-14]); (P = .03). There were no significant differences in the frequency of adverse events, endoleaks, or additional procedures required. CONCLUSIONS: When it is used in simple procedures such as infrarenal aneurysm repair, image-based fusion technology is feasible both in hybrid operating rooms and on mobile systems and leads to an overall 50% reduction in radiation dose. Fusion technology should become standard of care for centers attempting to maximize radiation dose reduction, even if capital investment of a hybrid operating room is not feasible.

Phytoplankton adapt to changing ocean environments.

Model projections indicate that climate change may dramatically restructure phytoplankton communities, with cascading consequences for marine food webs. It is currently not known whether evolutionary change is likely to be able to keep pace with the rate of climate change. For simplicity, and in the absence of evidence to the contrary, most model projections assume species have fixed environmental preferences and will not adapt to changing environmental conditions on the century scale. Using 15 y of observations from Station CARIACO (Carbon Retention in a Colored Ocean), we show that most of the dominant species from a marine phytoplankton community were able to adapt their realized niches to track average increases in water temperature and irradiance, but the majority of species exhibited a fixed niche for nitrate. We do not know the extent of this adaptive capacity, so we cannot conclude that phytoplankton will be able to adapt to the changes anticipated over the next century, but community ecosystem models can no longer assume that phytoplankton cannot adapt.

Mutations in CYP24A1 and idiopathic infantile hypercalcemia.

BACKGROUND: Vitamin D supplementation for the prevention of rickets is one of the oldest and most effective prophylactic measures in medicine, having virtually eradicated rickets in North America. Given the potentially toxic effects of vitamin D, the recommendations for the optimal dose are still debated, in part owing to the increased incidence of idiopathic infantile hypercalcemia in Britain in the 1950s during a period of high vitamin D supplementation in fortified milk products. We investigated the molecular basis of idiopathic infantile hypercalcemia, which is characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. METHODS: We used a candidate-gene approach in a cohort of familial cases of typical idiopathic infantile hypercalcemia with suspected autosomal recessive inheritance. Identified mutations in the vitamin D-metabolizing enzyme CYP24A1 were evaluated with the use of a mammalian expression system. RESULTS: Sequence analysis of CYP24A1, which encodes 25-hydroxyvitamin D 24-hydroxylase, the key enzyme of 1,25-dihydroxyvitamin D(3) degradation, revealed recessive mutations in six affected children. In addition, CYP24A1 mutations were identified in a second cohort of infants in whom severe hypercalcemia had developed after bolus prophylaxis with vitamin D. Functional characterization revealed a complete loss of function in all CYP24A1 mutations. CONCLUSIONS: The presence of CYP24A1 mutations explains the increased sensitivity to vitamin D in patients with idiopathic infantile hypercalcemia and is a genetic risk factor for the development of symptomatic hypercalcemia that may be triggered by vitamin D prophylaxis in otherwise apparently healthy infants.

Ectopic lipid storage in non-alcoholic fatty liver disease is not mediated by impaired mitochondrial oxidative capacity in skeletal muscle.

Non-alcoholic fatty liver disease (NAFLD), characterized by lipid deposition within the liver [intrahepatocellular lipid (IHCL)], is associated with insulin resistance and the metabolic syndrome (MS). It has been suggested that impaired skeletal muscle mitochondrial function may contribute to ectopic lipid deposition, and the associated MS, by altering post-prandial energy storage. To test this hypothesis, we performed a cross-sectional study of 17 patients with NAFLD [mean±S.D.; age, 45±11 years; body mass index (BMI), 31.6±3.4 kg/m2] and 18 age- and BMI-matched healthy controls (age, 44±11 years; BMI, 30.5±5.2 kg/m2). We determined body composition by MRI, IHCL and intramyocellular (soleus and tibialis anterior) lipids (IMCLs) by proton magnetic resonance spectroscopy (1H-MRS) and skeletal muscle mitochondrial function by dynamic phosphorus magnetic resonance spectroscopy (31P-MRS) of quadriceps muscle. Although matched for BMI and total adiposity, after statistical adjustment for gender, patients with NAFLD (defined by IHCL ≥ 5.5%) had higher IHCLs (25±16% compared with 2±2%; P<0.0005) and a higher prevalence of the MS (76% compared with 28%) compared with healthy controls. Despite this, the visceral fat/subcutaneous fat ratio, IMCLs and muscle mitochondrial function were similar between the NAFLD and control groups, with no significant difference in the rate constants of post-exercise phosphocreatine (PCr) recovery (1.55±0.4 compared with 1.51±0.4 min-1), a measure of muscle mitochondrial function. In conclusion, impaired muscle mitochondrial function does not seem to underlie ectopic lipid deposition, or the accompanying features of the MS, in patients with NAFLD.

Higher extracellular fluid volume in women is concealed by scaling to body surface area.

OBJECTIVE: The objective was to assess body surface area (BSA) for scaling extracellular fluid volume (ECV) in comparison with estimated lean body mass (LBM) and total body water (TBW) across a range of body mass indices (BMI). METHODS: This was a multi-centre study from 15 centres that submitted raw data from routine measurement of GFR in potential kidney transplant donors. There were 819 men and 1059 women in total. ECV was calculated from slope-intercept and slope-only measurements of GFR. ECV was scaled using two methods: Firstly, division of ECV by the scaling variable (ratio method), and secondly the regression method of Turner and Reilly. Subjects were placed into five BMI groups: < 20, 20-24.9, 25-29.9, 30-34.9, and 35 + kg/m(2). LBM and TBW were estimated from previously published, gender-specific prediction equations. RESULTS: Ratio and regression scaling gave almost identical results. ECV scaled to BSA by either method was higher in men in all BMI groups but ECV scaled to LBM and TBW was higher in women. There was, however, little difference between men and women in respect to ECV per unit weight in any BMI group, even though women have 10% more adipose tissue. The relations between TBW and BSA and between LBM and BSA, but not between LBM and TBW, were different between men and women. CONCLUSION: Lean tissue in women contains more extracellular water than in men, a difference that is obscured by scaling to BSA. The likely problem with BSA is its insensitivity to body composition.

Density regulation amplifies environmentally induced population fluctuations.

Background: Density-dependent regulation is ubiquitous in population dynamics, and its potential interaction with environmental stochasticity complicates the characterization of the random component of population dynamics. Yet, this issue has not received attention commensurate with its relevance for descriptive and predictive modeling of population dynamics. Here we use a Bayesian modeling approach to investigate the contribution of density regulation to population variability in stochastic environments. Methods: We analytically derive a formula linking the stationary variance of population abundance/density under Gompertz regulation in a stochastic environment with constant variance to the environmental variance and the strength of density feedback, to investigate whether and how density regulation affects the stationary variance. We examine through simulations whether the relationship between stationary variance and density regulation inferred analytically under the Gompertz model carries over to the Ricker model, widely used in population dynamics modeling. Results: The analytical decomposition of the stationary variance under stochastic Gompertz dynamics implies higher variability for strongly regulated populations. Simulation results demonstrate that the pattern of increasing population variability with increasing density feedback found under the Gompertz model holds for the Ricker model as well, and is expected to be a general phenomenon with stochastic population models. We also analytically established and empirically validated that the square of the autoregressive parameter of the Gompertz model in AR(1) form represents the proportion of stationary variance due to density dependence. Discussion: Our results suggest that neither environmental stochasticity nor density regulation can alone explain the patterns of population variability in stochastic environments, as these two components of temporal variation interact, with a tendency for density regulation to amplify the magnitude of environmentally induced population fluctuations. This finding has far-reaching implications for population viability. It implies that intense intra-specific resource competition increases the risk of environment-driven population collapse at high density, making opportune harvesting a sensible practice for improving the resistance of managed populations such as fish stocks to environmental perturbations. The separation of density-dependent and density-independent processes will help improve population dynamics modeling, while providing a basis for evaluating the relative importance of these two categories of processes that remains a topic of long-standing controversy among ecologists.

Genomic architecture constrains macromolecular allocation in dinoflagellates.

Dinoflagellate genomes have a unique architecture that may constrain their physiological and biochemical responsiveness to environmental stressors. Here we quantified how nitrogen (N) starvation influenced macromolecular allocation and C:N:P of three photosynthetic marine dinoflagellates, representing different taxonomic classes and genome sizes. Dinoflagellates respond to nitrogen starvation by decreasing cellular nitrogen, protein and RNA content, but unlike many other eukaryotic phytoplankton examined RNA:protein is invariant. Additionally, 2 of the 3 species exhibit increases in cellular phosphorus and very little change in cellular carbon with N-starvation. As a consequence, N starvation induces moderate increases in C:N, but extreme decreases in N:P and C:P, relative to diatoms. Dinoflagellate DNA content relative to total C, N and P is much higher than similar sized diatoms, but similar to very small photosynthetic picoeukaryotes such as Ostreococcus. In aggregate these results indicate the accumulation of phosphate stores may be an important strategy employed by dinoflagellates to meet P requirements associated with the maintenance and replication of their large genomes.

The reliability of glomerular filtration rate measured from plasma clearance: a multi-centre study of 1,878 healthy potential renal transplant donors.

PURPOSE: The objective of the study was to undertake a clinical audit of departmental performance in the measurement of glomerular filtration rate (GFR) using the coefficient of variation (CV) of extracellular fluid volume (ECFV) as the benchmark. ECFV is held within narrow limits in healthy subjects, narrower than GFR, and should therefore have a low CV. METHODS: Fifteen departments participated in this retrospective study of healthy renal transplant donors. Data were analysed separately for men (n ranged from 28 to 115 per centre; total = 819) and women (n = 28-146; 1,059). All centres used the slope-intercept method with blood sample numbers ranging from two to five. Subjects did not fast prior to GFR measurement. GFR was scaled to body surface area (BSA) and corrected for the single compartment assumption. GFR scaled to ECFV was calculated as the terminal slope rate constant and corrected for the single compartment assumption. ECFV/BSA was calculated as the ratio of GFR/BSA to GFR/ECFV. RESULTS: The departmental CVs of ECFV/BSA and GFR/BSA ranged from 8.3 to 25.8% and 12.8 to 21.9%, respectively, in men, and from 9.6 to 21.1% and 14.8 to 23.7%, respectively, in women. Both CVs correlated strongly between men and women from the same centre, suggesting department-specific systematic errors. GFR/BSA was higher in men in 14 of 15 centres, whereas GFR/ECFV was higher in women in 14 of 15 centres. Both correlated strongly between men and women, suggesting regional variation in GFR. CONCLUSION: The CV of ECFV/BSA in normal subjects is a useful indicator of the technical robustness with which GFR is measured and, in this study, indicated a wide variation in departmental performance.

Extracellular fluid volume and glomerular filtration rate in 1878 healthy potential renal transplant donors: effects of age, gender, obesity and scaling.

UNLABELLED: Aim. The aim of this study was to investigate the influence of age, gender, obesity and scaling on glomerular filtration rate (GFR) and extracellular fluid volume (ECV) in healthy subjects. METHODS: This is a retrospective multi-centre study of 1878 healthy prospective kidney transplant donors (819 men) from 15 centres. Age and body mass index (BMI) were not significantly different between men and women. Slope-intercept GFR was measured (using Cr-51-EDTA in 14 centres; Tc-99m-DTPA in one) and scaled to body surface area (BSA) and lean body mass (LBM), both estimated from height and weight. GFR was also expressed as the slope rate constant, with one-compartment correction (GFR/ECV). ECV was measured as the ratio, GFR to GFR/ECV. RESULTS: ECV was age independent but GFR declined with age, at a significantly faster rate in women than men. GFR/BSA was higher in men but GFR/ECV and GFR/LBM were higher in women. Young women (<30 years) had higher GFR than young men but the reverse was recorded in the elderly (>65 years). There was no difference in GFR between obese (BMI>30 kg/m2) and non-obese men. Obese women, however, had lower GFR than non-obese women and negative correlations were observed between GFR and both BMI and %fat. The decline in GFR with age was no faster in obese versus non-obese subjects. ECV/BSA was higher in men but ECV/LBM was higher in women. ECV/weight was almost gender independent, suggesting that fat-free mass in women contains more extracellular water. BSA is therefore a misleading scaling variable. CONCLUSION: There are several significant differences in GFR and ECV between healthy men and women.

Evolutionary inheritance of elemental stoichiometry in phytoplankton.

The elemental composition of phytoplankton is a fusion of the evolutionary history of the host and plastid, resulting in differences in genetic constraints and selection pressures associated with environmental conditions. The evolutionary inheritance hypothesis predicts similarities in elemental composition within related taxonomic lineages of phytoplankton. To test this hypothesis, we measured the elemental composition (C, N, P, S, K, Mg, Ca, Sr, Fe, Mn, Zn, Cu, Co, Cd and Mo) of 14 phytoplankton species and combined these with published data from 15 more species from both marine and freshwater environments grown under nutrient-replete conditions. The largest differences in the elemental profiles of the species distinguish between the prokaryotic Cyanophyta and primary endosymbiotic events that resulted in the green and red plastid lineages. Smaller differences in trace element stoichiometry within the red and green plastid lineages are consistent with changes in trace elemental stoichiometry owing to the processes associated with secondary endosymbioses and inheritance by descent with modification.