Genetic diversity and population structure in two species of sea cucumber: differing patterns according to mode of development

The population structure of two species of sea cucumber was examined based on mitochondrial DNA sequence analysis. Cucumaria miniata , a species with pelagic nonfeeding larvae lasting less than 2 weeks, and C. pseudocurata , a brooding species lacking a pelagic phase, both occur over similar wide ranges of the northeastern Pacific between Alaska and California. No significant genetic structuring was observed among C. miniata samples with 95% of the observed nucleotide variance attributable to that within population samples. Conversely, only 3.4% of the observed variance was attributed to that within C. pseudocurata population samples, with sampling sites typically greater than 100 km apart. At a finer scale, two C. pseudocurata population samples taken 5 km apart were not statistically different. A significant genetic disjunction was observed among populations of the brooding species, but not in species with pelagic larvae, north of Vancouver Island, Canada, corresponding to the splitting of the California and Alaska currents. Given the observed high levels of genetic diversity in northern samples, this genetic break indicates survival in northern, as well as southern, Pleistocene refugia. These results clearly demonstrate the effects that changes in life-history patterns can have on dispersal, population structure, and the potential for speciation events.     

Preliminary estimates of the potential for carbon mitigation in European soils through no-till farming

In this paper we estimate the European potential for carbon mitigation of no-till farming using results from European tillage experiments. Our calculations suggest some potential in terms of (a) reduced agricultural fossil fuel emissions, and (b) increased soil carbon sequestration. We estimate that 100% conversion to no-till farming would be likely to sequester about 23 Tg C y^–1 in the European Union or about 43 Tg C y^–1 in the wider Europe (excluding the former Soviet Union). In addition, up to 3.2 Tg C y^–1 could be saved in agricultural fossil fuel emissions. Compared to estimates of the potential for carbon sequestration of other carbon mitigation options, no-till agriculture shows nearly twice the potential of scenarios whereby soils are amended with organic materials. Our calculations suggest that 100% conversion to no-till agriculture in Europe could mitigate all fossil fuel-carbon emissions from agriculture in Europe. However, this is equivalent to only about 4.1% of total anthropogenic CO₂-carbon produced annually in Europe (excluding the former Soviet Union) which in turn is equivalent to about 0.8% of global annual anthropogenic CO₂-carbon emissions.     

Energy Metabolism and Pyridine Nucleotide Levels during Xenopus Oocyte Maturation*, 1

The rate of oxygen consumption increased in maturing Xenopus oocytes within 2 hr after progesterone addition, well before GVBD. This suggested an early requirement for energy metabolism during maturation, similar to the situation in sea urchin eggs during fertilization. Yet, the absence of similar increases in glucose-6-phosphate levels, glucose-6-phosphate dehydrogenase activity, glucose conversion to CO₂, and the conversion of NAD(H) to NADP(H), indicated that carbohydrate metabolism was not being stimulated in Xenopus oocytes during maturation. The oxidation of other energy yielding substrates is discussed which might account for the finding that, within 5 min of progesterone addition, both reduced forms of the pyridine nucleotides increased 20% over control levels. This was later followed by a drop in NADH levels and a rise in NAD relative to controls. The significance of these changes in pyridine nucleotide levels and their relationship to a number of maturation events are discussed.     

Effect of stand age on greenhouse gas fluxes from a Sitka spruce [Picea sitchensis (Bong.) Carr.] chronosequence on a peaty gley soil

The influence of forest stand age in a Picea sitchensis plantation on (1) soil fluxes of three greenhouse gases (GHGs – CO₂, CH₄ and N₂O) and (2) overall net ecosystem global warming potential (GWP), was investigated in a 2‐year study. The objective was to isolate the effect of forest stand age on soil edaphic characteristics (temperature, water table and volumetric moisture) and the consequent influence of these characteristics on the GHG fluxes. Fluxes were measured in a chronosequence in Harwood, England, with sites comprising 30‐ and 20‐year‐old second rotation forest and a site clearfelled (CF) some 18 months before measurement. Adjoining unforested grassland (UN) acted as a control. Comparisons were made between flux data, soil temperature and moisture data and, at the 30‐year‐old and CF sites, eddy covariance data for net ecosystem carbon (C) exchange (NEE). The main findings were: firstly, integrated CO₂ efflux was the dominant influence on the GHG budget, contributing 93–94% of the total GHG flux across the chronosequence compared with 6–7% from CH₄ and N₂O combined. Secondly, there were clear links between the trends in edaphic factors as the forest matured, or after clearfelling, and the emission of GHGs. In the chronosequence sites, annual fluxes of CO₂ were lower at the 20‐year‐old (20y) site than at the 30‐year‐old (30y) and CF sites, with soil temperature the dominant control. CH₄ efflux was highest at the CF site, with peak flux 491±54.5 μg m⁻² h⁻¹ and maximum annual flux 18.0±1.1 kg CH₄ ha⁻¹ yr⁻¹. No consistent uptake of CH₄ was noted at any site. A linear relationship was found between log CH₄ flux and the closeness of the water table to the soil surface across all sites. N₂O efflux was highest in the 30y site, reaching 108±38.3 μg N₂O‐N m⁻² h⁻¹ (171 μg N₂O m⁻² h⁻¹) in midsummer and a maximum annual flux of 4.7±1.2 kg N₂O ha⁻¹ yr⁻¹ in 2001. Automatic chamber data showed a positive exponential relationship between N₂O flux and soil temperature at this site. The relationship between N₂O emission and soil volumetric moisture indicated an optimum moisture content for N₂O flux of 40–50% by volume. The relationship between C : N ratio data and integrated N₂O flux was consistent with a pattern previously noted across temperate and boreal forest soils.     

Quantitative variability of 342 plasma proteins in a human twin population

The degree and the origins of quantitative variability of most human plasma proteins are largely unknown. Because the twin study design provides a natural opportunity to estimate the relative contribution of heritability and environment to different traits in human population, we applied here the highly accurate and reproducible SWATH mass spectrometry technique to quantify 1,904 peptides defining 342 unique plasma proteins in 232 plasma samples collected longitudinally from pairs of monozygotic and dizygotic twins at intervals of 2–7 years, and proportioned the observed total quantitative variability to its root causes, genes, and environmental and longitudinal factors. The data indicate that different proteins show vastly different patterns of abundance variability among humans and that genetic control and longitudinal variation affect protein levels and biological processes to different degrees. The data further strongly suggest that the plasma concentrations of clinical biomarkers need to be calibrated against genetic and temporal factors. Moreover, we identified 13 cis‐SNPs significantly influencing the level of specific plasma proteins. These results therefore have immediate implications for the effective design of blood‐based biomarker studies.