Feeding habits of the tiger shark, <Emphasis Type="Italic">Galeocerdo cuvier,</Emphasis> in the northwest Atlantic Ocean and Gulf of Mexico

Tiger sharks, Galeocerdo cuvier, are apex predators that may structure marine communities through predation. Despite a large number of studies in other areas such as the Pacific Ocean, there are no quantitative data on the diet of tiger sharks in the northwest Atlantic Ocean and Gulf of Mexico. Diet was assessed from 169 tiger sharks by life stage, area, and environmental factors. Fifteen prey groups were identified, with teleosts, molluscs, birds, cephalopods, and reptiles being the predominant prey categories. There was an ontogenetic shift in diet, prey size and diversity. Molluscs were the most common prey in smaller sharks, while teleosts and reptiles became more important in the diet of larger sharks. Dietary overlap was significant by area (Gulf of Mexico vs Atlantic Ocean) and among all life stages except for young-of-the-year and adult tiger sharks. Juvenile tiger sharks also demonstrated selective feeding by targeting gastropod feet over ingesting the entire animal. While results were similar to feeding studies conducted on tiger sharks in other ocean basins, an understanding of area-specific trophic interactions is necessary to inform decision support tools for ecosystem-based approaches to management.     

Control of Oxidative Sulfur Metabolism of Chlorobium limicola forma thiosulfatophilum

A metered blend of anaerobic-grade N₂, CO₂, and H₂S gases was introduced into an illuminated, 800-ml liquid volume, continuously stirred tank reactor. The system, described as an anaerobic gas-to-liquid phase fed-batch reactor, was used to investigate the effects of H₂S flow rate and light energy on the accumulation of oxidized sulfur compounds formed by the photoautotroph Chlorobium limicola forma thiosulfatophilum during growth. Elemental sulfur was formed and accumulated in stoichiometric quantities when light energy and H₂S molar flow rate levels were optimally adjusted in the presence of nonlimiting CO₂. Deviation from the optimal H₂S and light energy levels resulted in either oxidation of sulfur or complete inhibition of sulfide oxidation. Based on these observations, a model of sulfide and sulfur oxidases electrochemically coupled to the photosynthetic reaction center of Chlorobium spp. is presented. The dynamic deregulation of oxidative pathways may be a mechanism for supplying the photosynthetic reaction center with a continuous source of electrons during periods of varying light and substrate availability, as in pond ecosystems where Chlorobium spp. are found. Possible applications for a sulfide gas removal process are discussed.     

Rates of growth and protein synthesis correlated with nucleic acid content in fry of rainbow trout, Oncorhynchus mykiss: effects of age and temperature

Groups of recently hatched fry of rainbow trout, Oncorhynchus mykiss were maintained in the laboratory in order to investigate the effects of age, ration level and temperature on whole body growth, nucleic acid concentrations, protein synthesis rates and enzyme activities. In fry of up to 30 days after hatching, which were feeding but still had some yolk sac, no significant change in mean RNA concentration was observed with ration level. In older fry of 50 days or more, when the yolk sac was completely absorbed and exogenous feeding fully established, the concentration of RNA was correlated with the rate of protein growth. RNA concentrations and activities of citrate synthase and lactate dehydrogenase were significantly different between fed and starved fry. As water temperature was raised (from 5 to 15° C), higher rates of protein growth were brought about by an increase in the rate of protein synthesis and also by increased efficiency of retention of synthesized protein (reduced protein turnover). In fed fry, no change in RNA concentration was found with increasing temperature, while the amount of RNA per cell (RNA: DNA) decreased, indicating that increased rates of protein synthesis were due to increased RNA efficiency.     

Substrate preferences of coexisting invasive amphipods, <Emphasis Type="Italic">Dikerogammarus villosus</Emphasis> and <Emphasis Type="Italic">Dikerogammarus haemobaphes</Emphasis>, under field and laboratory conditions

Two Ponto-Caspian amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, have expanded their geographical ranges from eastern Europe into Great Britain in recent years. This study represents one of the first examining the distribution and habitat preferences of coexisting populations of D. haemobaphes and D. villosus via field and laboratory experiments in the UK. Field surveys of a recently invaded lowland reservoir in the UK are complimented with ex situ laboratory mesocosm experiments examining the substrate preferences of coexisting populations of D. villosus and D. haemobaphes. Results from the field study indicated that D. haemobaphes dominated the macroinvertebrate community within the reservoir and demonstrated a strong affinity for large cobble and artificial substrates. D. villosus occurred at lower abundances but displayed a strong preference for coarse cobble substrates. A third invasive amphipod, Crangonyx pseudogracilis, was largely confined to sand/silt habitats. Laboratory mesocosm experiments clearly supported the field observations of D. villosus and D. haemobaphes with both species demonstrating a preference for cobble substrates. Results from the study highlight the importance of characterising physical habitat when investigating biological invasions and suggest that habitat availability may influence the extent and speed at which range expansion of new amphipod invaders occurs.     

Sessile invertebrate coelobite communities from reefs of Bermuda: Species composition and distribution

Sessile invertebrate coelobite communities attached to the walls and roof of cavities in coralgal reefs on the annular rim of the Bermuda platform near North Rock (4 sites) and in the algal cup reef tract on the south shore (3 sites) have been studied by belt photo-transects and direct sampling. Irradiance measurements reveal a light gradient which appears to exert a strong influence on the composition, relative coverage and zonation of the attached biotic communities. Two main communities are recognised from cluster analysis and relative areal coverage data. Near the cavity entrances is a community dominated by crustose coralline algae, with subsidiary ascidians, demosponges, bryozoans and Foraminifera. Species richness is high and there is total biotic coverage of walls and roof. This community grades laterally into an exclusively animal community characterised by encrusting sponges and Foraminifera, with subsidiary bryozoans and unidentified branching organisms. Coverage varies from 100% to 30%, the substrate often exhibiting high micro-relief from the branching growth forms of the Foraminifera. Species richness is high at North Rock sites, less so on the south shore. The distribution of coelobite species is compared with that described from previous studies in Bermuda, Grand Cayman and Madagascar.     

Determining the fate of selenium in wheat biofortification: an isotopically labelled field trial study

Background and aims

Root hair growth and development are important features of plant response to varying soil conditions and of nutrient and water uptake. Most current methods of characterizing root hairs in the field are unreliable or inefficient. We describe a method to quantify root hair area in digital images, such as those collected in situ by minirhizotron systems.

Methods

This method uses ImageJ and R open source software and is partially automated using code presented here. It requires manual tracing of a subset of root hair images (training data set) to which a multivariate logistic regression is fit with each color channel in the image as an independent variable. Thereafter the model is applied to complete sets of selected root hair sections to estimate total root hair area.

Results

There was good agreement between the training data sets and the predictions of the regression models in castor (Ricinus communis L.), maize (Zea mays L.), and papaya (Carica papaya L.).

Conclusion

This method enables time-efficient and consistent quantification of root hairs using in situ root imaging systems that are already widely in use.

     

Assessment of dietary intake: NuGO symposium report

Advances in genomics science and associated bioinformatics and technology mean that excellent tools are available for characterising human genotypes. At the same time, approaches for characterising individual phenotypes are developing rapidly. In contrast, there has been much less investment in novel methodology for measuring dietary exposures so that there is now a significant gap in the toolkit for those investigating how diet interacts with genotype to determine phenotype. This symposium reviewed the strengths and limitations of current tools used in assessment of dietary intake and the potential to improve these tools through, for example, the use of statistical techniques that combine information from different sources (such as modelling and calibration methods) to ameliorate measurement error and to provide validity checks. Speakers examined the use of approaches based on technologies such as mobile 'phones, digital cameras and Web-based systems which offer the potential for more acceptable (for study participants) and less laborious (for researchers and participants) routes to more robust data collection. In addition, the application of omics, especially metabolomics, tools to biofluids to identify new biomarkers of intake offers great potential to provide objective measures of food consumption with the advantage that data may be collected in forms that can be integrated readily with other high throughput (nutrigenomic) technologies.