Partitioning the effects of algal species identity and richness on benthic marine primary production

Influential research in terrestrial habitats indicates that several ecosystem processes are related to plant biodiversity, yet these links remain poorly studied in marine ecosystems. We conducted one field and one mesocosm experiment to quantify the relative effects of macroalgal species identity and richness on primary production in coral reef macroalgal communities off the north coast of Jamaica. We measured production as the net accumulation of algal biomass in the absence of consumers and as photosynthetic rate using oxygen probes in sealed aquaria. We used two recently developed techniques to attribute deviations in expected relative yield to components associated with species identity or diversity and then to further partition diversity effects into mechanistic components based on dominance, trait-dependent complementarity, and trait-independent complementarity. Our results indicate that algal identity had far greater effects on absolute net growth and photosynthesis than richness. The most diverse mixture of macroalgae did not outperform the most productive monoculture or the average monoculture in either measure of primary production (i.e. we did not find evidence of either transgressive or non-transgressive overyielding). Trait-independent complementarity effects were positive but dominance and trait-dependent complementarity were both negative and became stronger when richness was increased. Thus the potentially positive influence of species interactions and niche partitioning on production were negated by dominance and other negative selection effects. These results demonstrate that the counteracting influence of component effects can diminish the net richness effects on production. This could explain frequently observed weak net richness effects in other aquatic and terrestrial systems and suggests that life history tradeoffs greatly reduce the potential for ecologically relevant plant biodiversity effects on ecosystem properties.     

The role of foraging behaviour in the sexual segregation of the African elephant

Elephants (Loxodonta africana) exhibit pronounced sexual dimorphism, and in this study we test the prediction that the differences in body size and sociality are significant enough to drive divergent foraging strategies and ultimately sexual segregation. Body size influences the foraging behaviour of herbivores through the differential scaling coefficients of metabolism and gut size, with larger bodied individuals being able to tolerate greater quantities of low-quality, fibrous vegetation, whilst having lower mass-specific energy requirements. We test two distinct theories: the scramble competition hypothesis (SCH) and the forage selection hypothesis (FSH). Comprehensive behavioural data were collected from the Pongola Game Reserve and the Phinda Private Game Reserve in South Africa over a 2.5-year period. The data were analysed using sex as the independent variable. Adult females targeted a wider range of species, adopted a more selective foraging approach and exhibited greater bite rates as predicted by the body size hypothesis and the increased demands of reproductive investment (lactation and pregnancy). Males had longer feeding bouts, displayed significantly more destructive behaviour (31% of observations, 11% for females) and ingested greater quantities of forage during each feeding bout. The independent ranging behaviour of adult males enables them to have longer foraging bouts as they experience fewer social constraints than females. The SCH was rejected as a cause of sexual segregation due to the relative abundance of low quality forage, and the fact that feeding heights were similar for both males and females. However, we conclude that the differences in the foraging strategies of the sexes are sufficient to cause spatial segregation as postulated by the FSH. Sexual dimorphism and the associated behavioural differences have important implications for the management and conservation of elephant and other dimorphic species, with the sexes effectively acting as distinct “ecological species”.     

The difference in embryo quality between Belclare and Suffolk ewes is not due to differences in oocyte quality

We have previously reported that the percentage of fertilized oocytes which reached the blastocyst stage by Day 6 after AI with frozen-thawed semen was higher for Belclare (94%) than Suffolk (59%) ewes. This may reflect differences in the timing of fertilization (Experiment 1) or differences in oocyte quality (Experiments 2 and 3). In Experiment 1, oocytes recovered from slaughterhouse ovaries were matured in vitro for 18, 20, 24, 28 or 30 h prior to fertilization and were then cultured in vitro. In Experiment 2, Belclare (n = 69) and Suffolk (n = 71) ewes were laparoscopically inseminated using frozen-thawed semen. Presumptive zygotes were recovered between 23 and 47 h post-insemination and cultured in vitro (grouped by breed). In Experiment 3, immature oocytes from Suffolk and Belclare ewes, were matured, fertilized and cultured in vitro (grouped by breed). Cleavage rate and blastocyst development was assessed. There was no effect of time of fertilization on cleavage rate, however, a lower proportion of cleaved oocytes reached the blastocyst stage after insemination at 30h compared to 24 h (P < 0.001). Ewe breed did not affect cleavage rate of oocytes matured and fertilized in vivo (41+/-9.6 and 47+/-10.1) or in vitro (47+/-9.4 and 52+/-9.4) for Belclare and Suffolk ewes, respectively (P > 0.05; %+/-S.E.). Likewise, ewe breed had no effect on the percentage (+/-S.E.) of cleaved oocytes developing to the blastocyst stage for in vivo (29+/-7.2 and 25+/-7.9) or in vitro matured and fertilized oocytes (29+/-6.1 and 36+/-5.9) from Belclare and Suffolk ewes, respectively (P>0.05). Based on this study oocyte quality does not differ between the breeds and in addition a 4h difference in the timing of fertilization, reflective of the breed difference in the timing of the LH surge in vivo, would not affect early embryo development.     

Plasmodium falciparum: chondroitin sulfate A is the major receptor for adhesion of parasitized erythrocytes in the placenta

Plasmodium falciparum parasites that sequester in the placenta bind to the molecule chondroitin sulfate A (CSA). Women become resistant to malaria during pregnancy as they acquire antibodies that inhibit parasite adhesion to CSA, suggesting that a vaccine against placental malaria is feasible. Hyaluronic acid (HA) and non-immune IgG have also been proposed as receptors for P. falciparum adhesion in the placenta, but evidence for their roles is inconclusive. In this study, CSA, HA, and IgG were simultaneously assessed for their relative contributions to placental adhesion. Placental parasites collected in Tanzania uniformly adhered to the molecule CSA, and soluble CSA completely inhibited adhesion of most samples to placental cryosections. Three of 46 placental parasite samples also adhered to immobilized HA, but HA failed to inhibit adhesion of any placental parasites to placental cryosections. Similarly, non-immune IgG and protein A failed to inhibit adhesion of parasite samples to placental cryosection. P. falciparum adhesion in the placenta appears to be a non-redundant process that requires CSA as a receptor. Vaccines that elicit functional antibodies against CSA-binding parasites may confer resistance to pregnancy malaria.     

Effects of elevated temperature and nickel pollution on the immune status of Japanese medaka

Changes in a host's environment (i.e. physical or chemical) can alter normal immune function. In aquatic organisms, exposure to stress can result in significant changes in innate immunity. In the natural environment, fish are exposed to multiple stressors simultaneously. Temperature change and/or chemical exposure as individual environmental stressors have been shown in various fish species to alter all aspects of the immune response. These same stressors have also been shown to alter plasma steroid levels in exposed fish. For this study, the effects of elevated temperature and nickel pollution on specific immune parameters of Japanese medaka (Oryzias latipes) were determined. Fish were exposed for 1, 7 or 14d to either: waterborne nickel (Ni) at the nominal concentration of 125ppb; a 5 degrees C (+/-0.5 degrees C) rapid increase in water temperature; or, both potential stressors in combination. Medaka maintained at room temperature (25 degrees C+/-1 degrees C) served as the controls. Altered function of the innate and adaptive arms of the immune response was evaluated by assessing kidney macrophage-mediated superoxide (O(2)(-)) production and splenic T-cell proliferation, respectively. Plasma cortisol levels were analysed in the same fish as a marker of the physiological stress response. While kidney cell number was unaffected by exposure of fish to either stressor alone or both factors in combination, spleen cellularity was decreased (compared to control fish) in medaka exposed for 1d to thermal stress in combination with Ni, and to a lesser extent to thermal stress alone. T-lymphocyte proliferation by medaka splenocytes was not affected by any exposure paradigm. Unstimulated intracellular O(2)(-) production by kidney phagocytes was significantly elevated (compared to control) in medaka exposed for 1d to either thermal stress alone or temperature change in combination with Ni; by 7d, only the stressor combination significantly increased baseline O(2)(-) production. Resting levels of extracellular O(2)(-) production was significantly reduced in fish maintained for 1d at the elevated temperature. Effects on phorbol 12-myristate 13 acetate (PMA)-stimulated intracellular and extracellular O(2)(-) production were less dramatic than those observed for resting phagocytes. Exposure of medaka to elevated temperature for 14d tended (p<0.06) to reduce PMA-stimulated intracellular O(2)(-) production (compared to the time-matched control). Although exposure of fish for 14d to elevated temperature only slightly reduced stimulated extracellular O(2)(-) production, exposure for the same duration to Ni alone significantly depressed oxyradical production by kidney phagocytes (compared to the time-matched controls). Decreased plasma cortisol levels were observed in fish exposed for 7d to either an elevated water temperature or Ni (compared to the time-matched control); by 14d of exposure, no significant treatment-induced effects on cortisol levels were observed. These findings add to the growing body of literature seeking to determine what effects, if any, exposure to multiple aquatic pollution-induced effects have upon fish health and the health of impacted ecosystems.     

Total antioxidant power in sled dogs supplemented with blueberries and the comparison of blood parameters associated with exercise

Oxidative damage from free radicals plays an important role in several diseases such as cancer, Alzheimer's disease, and heart disease. Research indicates that exercise contributes to oxidative stress. Fruits, such as blueberries, are good antioxidants because they contain phenolics that preferentially react with free radicals. Maintaining antioxidant levels by supplementing the diet with blueberries may prevent exercise-induced oxidative damage. The goal of our study was to compare antioxidant levels in sled dogs supplemented with blueberries on blood parameters within 48 h post-exercise. Though the exercise protocol did not cause unusual muscle damage as reflected in plasma creatine kinase and isoprostane levels, blueberry supplementation did elicit significantly elevated antioxidant status in sled dogs post exercise. This suggests that dogs fed blueberries while exercising as compared to dogs fed a control diet while exercising, may be better protected against oxidative damage.     

Comparative maturation of cynomolgus monkey oocytes in vivo and in vitro

Background  

In vitro maturation (IVM) of oocytes followed by fertilization in vitro (IVF) and embryo transfer offers an alternative to conventional IVF treatment that minimises drug administration and avoids ovarian hyperstimulation. However, the technique is less efficient than maturation in vivo. In the present study, a non-human primate model was used to address the hypothesis that the number of oocytes is increased and their nuclear and cytoplasmic maturity after IVM are improved when maturation is initiated in vivo by priming with hCG.     

Formation of the gap junction nexus: binding partners for connexins.

Gap junctions are the morphological correlates of direct cell-cell communication and are formed of hexameric assemblies of gap junction proteins (connexins) into hemichannels (or connexons) provided by each coupled cell. Gap junction channels formed by each of the connexin subtypes (of which there are as many as 20) display different properties, which have been attributed to differences in amino acid sequences of gating domains of the connexins. Recent studies additionally indicate that connexin proteins interact with other cellular components to form a protein complex termed the Nexus. This review summarizes current knowledge regarding the protein-protein interactions involving of connexin proteins and proposes hypothesized functions for these interactions.     

The photoprotective molecular switch in the photosystem II antenna

We have reviewed the current state of multidisciplinary knowledge of the photoprotective mechanism in the photosystem II antenna underlying non-photochemical chlorophyll fluorescence quenching (NPQ). The physiological need for photoprotection of photosystem II and the concept of feed-back control of excess light energy are described. The outline of the major component of nonphotochemical quenching, qE, is suggested to comprise four key elements: trigger (ΔpH), site (antenna), mechanics (antenna dynamics) and quencher(s). The current understanding of the identity and role of these qE components is presented. Existing opinions on the involvement of protons, different LHCII antenna complexes, the PsbS protein and different xanthophylls are reviewed. The evidence for LHCII aggregation and macrostructural reorganization of photosystem II and their role in qE are also discussed. The models describing the qE locus in LHCII complexes, the pigments involved and the evidence for structural dynamics within single monomeric antenna complexes are reviewed. We suggest how PsbS and xanthophylls may exert control over qE by controlling the affinity of LHCII complexes for protons with reference to the concepts of hydrophobicity, allostery and hysteresis. Finally, the physics of the proposed chlorophyll-chlorophyll and chlorophyll-xanthophyll mechanisms of energy quenching is explained and discussed. This article is part of a Special Issue entitled: Photosystem II.