Phytoplankton is a nineteenth century ecological construct for a biologically diverse group of pelagic photoautotrophs that share common metabolic functions but not evolutionary histories. In contrast to terrestrial plants, a major schism occurred in the evolution of the eukaryotic phytoplankton that gave rise to two major plastid superfamilies. The green superfamily appropriated chlorophyll b, whereas the red superfamily uses chlorophyll c as an accessory photosynthetic pigment. Fossil evidence suggests that the green superfamily dominated Palaeozoic oceans. However, after the end-Permian extinction, members of the red superfamily rose to ecological prominence. The processes responsible for this shift are obscure. Here we present an analysis of major nutrients and trace elements in 15 species of marine phytoplankton from the two superfamilies. Our results indicate that there are systematic phylogenetic differences in the two plastid types where macronutrient (carbon:nitrogen:phosphorus) stoichiometries primarily reflect ancestral pre-symbiotic host cell phenotypes, but trace element composition reflects differences in the acquired plastids. The compositional differences between the two plastid superfamilies suggest that changes in ocean redox state strongly influenced the evolution and selection of eukaryotic phytoplankton since the Proterozoic era.

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.

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Under optimal growth conditions, many metabolic rates scale to the 3 ⁄ 4 power of mass. We show that resource limitation can alter this size scaling of metabolic rates if resource acquisition depends on organism size. A prime example of size-dependent resource acquisition is light harvesting by phytoplankton. The size-dependence of light acquisition causes a deviation in the 3 ⁄ 4 size scaling of growth and photosynthetic rates under growth-limiting irradiance. The degree of deviation from the 3 ⁄ 4 size-scaling exponent depends on the size-dependence of physiological acclimation in response to resource limitation. Phytoplankton acclimate to light limitation by changes in pigment concentration. We calculate the pigment concentration required to maximize photosynthetic rate, and predict that the light-limited photosynthetic rate must scale to the 2 ⁄ 3 power of cell volume. These theoretical results are consistent with the size scaling of pigment concentration and photosynthetic rate of phytoplankton cultures. Our results suggest that deviation from the 3 ⁄ 4 size-scaling exponent for metabolic rate under resource-limiting conditions is the consequence of the size-dependence of both resource acquisition and physiological acclimation to resource availability. KEY WORDS: 3 ⁄ 4 rule · Allometry · Light absorption · Macroecology · Nutrient uptake · Phytoplankton · Resource limitation · Size scaling Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 273: [269][270][271][272][273][274][275][276][277][278][279] 2004 ties of transport networks (West et al. 1997, Banavar et al. 2002. West et al. (1997) argued that fractal transport networks regulate metabolic rates with a maximum possible size-scaling exponent of 3 ⁄ 4 . They observed that many biological surfaces are effectively fractal and thus have non-Euclidean scaling. They modify a surface-rule argument to obtain a scaling exponent of 3 ⁄ 4 instead of 2 ⁄ 3 . Banavar et al. (2002) show that an efficient Euclidean resource delivery network which allows metabolic rate to be independent of organism size must itself scale as V 4 ⁄ 3 . In many organisms, the transport network is an approximately constant proportion of body mass, and thus the metabolic rate scales to the 3 ⁄ 4 power of body volume or mass (Banavar et al. 2002). However, every rule has exceptions. Deviations in the size-scaling exponent have been associated with sub-optimal environmental conditions, such as extremes in temperature and irradiance (Schlesinger et al. 1981, Peters 1983, Sommer 1989, Finkel 2001, Gillooly et al. 2001. Theoretical models based on geometric scaling properties of transport networks suggest that imbalances in supply and demand could cause deviations from the 3 ⁄ 4 rule (Banavar et al. 2002). Under resource limitation, the supply of energy and nutrients does not match the demands of growth rate. There is at present no theoretical description of how resource limitation will alter the size scaling of metabolic rates.Under o...

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 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), 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.arth system models (ESMs) generally indicate that greenhouse gas emissions may, over the coming century, lead to further acidification and warming of the ocean surface, increased surface stratification and decreased mixing depths, and weaker seasonal entrainment of deep nutrients essential for phytoplankton growth (1, 2). These global trends are seen in the North Atlantic, although regional variations are apparent (Fig. S1). Many models project that waters southeast of Greenland will become cooler, more stratified, and consequently nutrient-poor (1-3). Here, strong salinity-driven surface stratification arising from ice melt and enhanced precipitation over evaporation may weaken meridional overturning (4). The cooling here is associated with weaker transport of heat into the surface laterally and from below by convection but is also because stratified surface waters are exposed to the relatively cold atmosphere for a longer duration (5). Projected basin-scale changes in clouds and sea ice cover may also drive changes in light entering the ocean surface.These environmental changes may lead to pronounced regional changes in phytoplankton communities, overlying a global trend of decreasing primary production, weaker sinking flux of particulate carbon, and decreased energy flows between phytoplankton and fish (1, 2, 6). Although it is widely believed that marine organisms and ecosystems are sensitive to climate change (7-11), the climate response and drivers of change for individual phytoplankton species are not well known. The goal of this study is to estimate how anthropogenic climate change in the coming century may alter the biogeographies of many phytoplankton species commonly sampled in the subpolar...

Glucagon-like peptide-1 receptor agonists (GLP-1 RA) are effective for obese patients with type 2 diabetes mellitus (T2DM) because they concomitantly target obesity and dysglycaemia. Considering the high prevalence of non-alcoholic fatty liver disease (NAFLD) in patients with T2DM, we determined the impact of 6 months’ GLP-1 RA therapy on intrahepatic lipid (IHL) in obese, T2DM patients with hepatic steatosis, and evaluated the inter-relationship between changes in IHL with those in glycosylated haemoglobin (HbA1c), body weight, and volume of abdominal visceral and subcutaneous adipose tissue (VAT and SAT). We prospectively studied 25 (12 male) patients, age 50±10 years, BMI 38.4±5.6 kg/m2 (mean ± SD) with baseline IHL of 28.2% (16.5 to 43.1%) and HbA1c of 9.6% (7.9 to 10.7%) (median and interquartile range). Patients treated with metformin and sulphonylureas/DPP-IV inhibitors were given 6 months GLP-1 RA (exenatide, n = 19; liraglutide, n = 6). IHL was quantified by liver proton magnetic resonance spectroscopy (1H MRS) and VAT and SAT by whole body magnetic resonance imaging (MRI). Treatment was associated with mean weight loss of 5.0 kg (95% CI 3.5,6.5 kg), mean HbA1c reduction of 1·6% (17 mmol/mol) (0·8,2·4%) and a 42% relative reduction in IHL (−59.3, −16.5%). The relative reduction in IHL correlated with that in HbA1c (ρ = 0.49; p = 0.01) but was not significantly correlated with that in total body weight, VAT or SAT. The greatest IHL reduction occurred in individuals with highest pre-treatment levels. Mechanistic studies are needed to determine potential direct effects of GLP-1 RA on human liver lipid metabolism.

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The elemental stoichiometry of microalgae reflects their underlying macromolecular composition and influences competitive interactions among species and their role in the food web and biogeochemistry. Here we provide a new estimate of the macromolecular composition of microalgae using a hierarchical Bayesian analysis of data compiled from the literature. The median macromolecular composition of nutrient-sufficient exponentially growing microalgae is 32.2% protein, 17.3% lipid, 15.0% carbohydrate, 17.3% ash, 5.7% RNA, 1.1% chlorophyll-a and 1.0% DNA as percent dry weight. Our analysis identifies significant phylogenetic differences in macromolecular composition undetected by previous studies due to small sample sizes and the large inherent variability in macromolecular pools. The phylogenetic differences in macromolecular composition lead to variations in carbon-to-nitrogen ratios that are consistent with independent observations. These phylogenetic differences in macromolecular and elemental composition reflect adaptations in cellular architecture and biochemistry; specifically in the cell wall, the light harvesting apparatus, and storage pools.