Vertical Flux of Biogenic Carbon in the Ocean: Is There Food Web Control?

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.     

Differential responses of body shape to local and reach scale stream flow in two freshwater fish species

Stream flow is recognised as an important influence on the physical traits, distribution and diversity of stream fishes. However, measures of ‘stream flow’ are not consistent among studies and can refer to variables characterising microhabitat (e.g. flow velocity) or reach‐level (e.g. discharge) parameters. Because of the ambiguity associated with the term ‘stream flow’, the differential effect of these two aspects of local stream hydrology on freshwater fishes is unclear. Using two frequently sympatric freshwater fish species, Etheostoma nigrum and Pimephales notatus, we tested for correlations between population‐level body shape and two measures of stream flow, microhabitat flow velocity (m/s) and reach‐level discharge (m³·s^?1). Etheostoma nigrum body shape was correlated with flow velocity, while P. notatus body shape was correlated with mean annual discharge. The respective correlations are potentially manifestations of behavioural differences among the two species. Etheostoma nigrum is a benthic specialist rarely venturing far from its associated microhabitats. Pimephales notatus is a habitat generalist and uses many different microhabitats but is unable to escape the overall discharge pressures of a particular stream. These results demonstrate the importance of considering the spatial scale of variables when predicting phenotype–environment associations.     

Precipitate formation in the strontium-phosphate system

Study of the precipitation process in the aqueous Sr(OH)(2)-H(3)PO(4) system, in order to elucidate the phase transformations and the nature of the final solid phases, shows that over much of the range of compositions studied the initial precipitate is poorly crystalline; the x-ray pattern resembles that of strontium hydroxyapatite but has a strontium: phosphorus molar ratio close to 1.3. Within 1 hour the initial precipitate changes to a stable crystalline phase (or phases), with corresponding change, either up or down, in the strontium: phosphorus ratio. At high ratios of Sr(OH)(2) to H(2)PO(4) the initial precipitate is Sr(3)(PO(4))(2)-4H(2)O, which then converts to a phase having the x-ray diffraction pattern of strontium hydroxyapatite, but having a strontium: phosphorus ratio that depends somewhat on the initial ratio of Sr(OH)(2) to H(3)PO(4) used in the precipitation.     

HLA and NK cell inhibitory receptor genes in resolving hepatitis C virus infection

Natural killer (NK) cells provide a central defense against viral infection by using inhibitory and activation receptors for major histocompatibility complex class I molecules as a means of controlling their activity. We show that genes encoding the inhibitory NK cell receptor KIR2DL3 and its human leukocyte antigen C group 1 (HLA-C1) ligand directly influence resolution of hepatitis C virus (HCV) infection. This effect was observed in Caucasians and African Americans with expected low infectious doses of HCV but not in those with high-dose exposure, in whom the innate immune response is likely overwhelmed. The data strongly suggest that inhibitory NK cell interactions are important in determining antiviral immunity and that diminished inhibitory responses confer protection against HCV.     

Characterization of alfalfa (Medicago sativa L.) following in vitro selection for salt tolerance

Summary Alfalfa (Medicago sativa L.) is a valuable forage crop which is grown in areas of limited rainfall, high temperature and where the land is often salt affected. Seedlings of the commercial variety CUF 101 and the more salt tolerant breeding line CUF101-1S were used as explant material to produce tissue cultures for an in vitro screen for salt tolerance. Callus cultures were placed on a regeneration medium containing 0–350 mol m^-3 NaCl to establish the highest possible salt concentration that would allow buds to regenerate and survive as plantlets. Buds were regenerated in 250 mol m^-3 NaCl then isolated, grown to maturity and set seed. The response to salt tolerance in the short term was investigated by exposing 14-day-old seedlings to 200 mol m^-3 NaCl. Measurement of growth, survival, proline concentration and the activity of antioxidant enzymes were made after 14 days exposure to NaCl. One somaclone in particular (6R2IV) compared with the parent line showed increased salt tolerance, greater accumulation of proline and a greater increase in the antioxidant enzyme, glutathione reductase. A potentially important gene is pA9 which is known to be responsible for the production of a proline rich cell wall protein. Polymerase Chain Reaction (PCR) amplification of a region of the pA9 gene indicated that it was present in both tolerant and sensitive lines. Southern blotting has shown that the copy number of the pA9 was present as multiple copies in the tolerant clone compared with a single copy in the parents.Abbreviations GR glutathione reductase     

Dietary Fat Supplementation and the Consequences for Oocyte and Embryo Quality: Hype or Significant Benefit for Dairy Cow Reproduction?

In many countries, fat supplementation in the diet has become common in the dairy industry. There are several ideas as to how dietary fat could influence reproductive performance. Saturated fatty acids, such as palm oil, can increase milk yield but may aggravate negative energy balance and thus may impair fertility when fed during the first week post‐partum. However, priming the lipid oxidation in the liver by feeding saturated fats during the dry period has recently been shown to be a potentially promising strategy to mitigate fat mobilization and liver accumulation post‐partum. Furthermore, polyunsaturated fats (omega‐3 fatty acids and conjugated linoleic acids) are fed to reduce the ‘de novo’ fat synthesis in the udder and thus the milk fat content, which may be of modest benefit for overall energy balance. Furthermore, omega‐6 and omega‐3 polyunsaturated fatty acids are reported to alter follicular growth, steroid synthesis and prostaglandin metabolism in the ovary and endometrium, respectively. Omega‐6 fatty acids are believed to have pro‐inflammatory and thus PGF2α‐stimulating properties rendering them extra value as ‘nutraceutical’ early post‐partum, while omega‐3 fatty acids can weaken this inflammatory potency, leading to a higher chance of survival of the embryo when supplemented during the periconceptual period. Unfortunately, research results rarely provide a consensus in this perspective. The consequences of these fat‐feeding strategies on oocyte and embryo quality remain an intriguing issue for debate. Fat feeding may alter the microenvironment of the growing and maturing oocyte of the early and older embryo and thus may affect reproductive outcome. We recently reported that dietary‐induced hyperlipidaemic conditions can be harmful for embryo development and metabolism. However, to date, research results remain somewhat conflicting most probably due to differences in fat sources used, in diet and duration of supplementation and in experimental set‐up in general.