A multi-mutualist simulation: Applying biological market models to diverse mycorrhizal communities

We present a cellular automaton that simulates the interaction between a host tree and multiple potential mycorrhizal symbionts and generates testable hypotheses of how processes at the scale of individual root tips may explain mycorrhizal community composition. Existing theoretical biological market models imply that a single host is able to interact with and select from multiple symbionts to organize an optimal symbiont community. When evaluating the tree–symbiont interaction, two scales must be considered simultaneously: the scale of the entire host plant at which carbon utilization and nutrient demands operate, and the scale of the individual root tip, at which colonization and carbon-nutrient trade occurs. Three strategies that may be employed by the host tree for optimizing carbon use and nutrient acquisition through mycorrhizal symbiont communities are simulated: (1) carbon pool adjustment, in which the plant controls only the total amount of carbon to be distributed uniformly throughout the root system, (2) symbiont selection, wherein the plant opts either for or against the interaction at each fine root tip, and (3) selective carbon allocation, wherein the plant adjusts the amount of carbon allocated to each root tip based on the cost of nutrients. Strategies were tested over various nutrient availabilities (the amount of inorganically and organically bound nutrients). Success was defined on the basis of minimizing carbon expended for nutrient acquisition because this would allow more carbon to be utilized for growth and reproduction. In all cases, the symbiont selection and selective carbon allocation strategies were able to meet the nutritional requirements of the plant, but did not necessarily optimize carbon use. The carbon pool adjustment strategy is the only strategy that does not operate at the individual root tip scale, and the strategy was not successful when inorganic nutrients were scarce since there is no mechanism to exclude suboptimal symbionts. The combination of the symbiont selection strategy and the carbon pool adjustment resulted in optimal carbon use and nutrient acquisition under all environmental conditions but result in monospecific symbiont assemblages. On the other hand, the selective carbon allocation strategy is the only strategy that maintained successful, multi-symbiont communities. The simulations presented here thus imply clear hypotheses about the effect of nutrient availability on symbiont selection and mycorrhizal community richness and composition.     

Earthworms and in vitro physiologically-based extraction tests: complementary tools for a holistic approach towards understanding risk at arsenic-contaminated sites

The relationship of the total arsenic content of a soil and its bioaccumulation by earthworms (Lumbricus rubellus and Dendrodrilus rubidus) to the arsenic fraction bioaccessible to humans, measured using an in vitro physiologically-based extraction test (PBET), was investigated. Soil and earthworm samples were collected at 24 sites at the former arsenic mine at the Devon Great Consols (DGC) in southwest England (UK), along with an uncontaminated site in Nottingham, UK, for comparison. Analysis of soil and earthworm total arsenic via inductively coupled plasma mass spectrometry (ICP-MS) was performed following a mixed acid digestion. Arsenic concentrations in the soil were elevated (204–9,025 mg kg⁻¹) at DGC. The arsenic bioaccumulation factor (BAF) for both earthworm species was found to correlate positively with the human bioaccessible fraction (HBF), although the correlation was only significant (P ≤ 0.05) for L. rubellus. The potential use of both in vitro PBETs and earthworms as complementary tools is explored as a holistic and multidisciplinary approach towards understanding risk at contaminated sites. Arsenic resistant earthworm species such as the L. rubellus populations at DGC are presented as a valuable tool for understanding risk at highly contaminated sites.     

Provenance and threat-sensitive predator avoidance patterns in wild-caught Trinidadian guppies

The antipredator behaviour of prey organisms is shaped by a series of threat-sensitive trade-offs between the benefits associated with successful predator avoidance and a suite of other fitness-related behaviours such as foraging, mating and territorial defence. Recent research has shown that the overall intensity of antipredator response and the pattern of threat-sensitive trade-offs are influenced by current conditions, including variability in predation risk over a period of days to weeks. In this study, we tested the hypothesis that long-term predation pressure will likewise have shaped the nature of the threat-sensitive antipredator behaviour of wild-caught Trinidadian guppies (Poecilia reticulata). Female guppies were collected from two populations that have evolved under high- and low-predation pressure, respectively, in the Aripo River, Northern Mountain Range, Trinidad. Under laboratory conditions, we exposed shoals of three guppies to varying concentrations of conspecific damage-released chemical alarm cues. Lower Aripo (high-predation) guppies exhibited the strongest antipredator response when exposed to the highest alarm cue concentration and a graded decline in response intensity with decreasing concentrations of alarm cue. Upper Aripo (low-predation) guppies, however, exhibited a nongraded (hypersensitive) response pattern. Our results suggest that long-term predation pressure shapes not only the overall intensity of antipredator responses of Trinidadian guppies but also their threat-sensitive behavioural response patterns.     

Distribution of hexabromocyclododecane in Detroit River suspended sediments

The distribution of hexabromocyclododecane (HBCD) isomers (alpha, beta and gamma) was determined in Detroit River suspended sediments using liquid chromatography tandem mass spectrometry (LC/MS/MS). Individual isomers of HBCD were measured at concentrations ranging from <0.025 to 1.9 ng/g (dry wt.) for the alpha-isomer, <0.025 to 0.28 ng/g for the beta-isomer, and <0.025 to 2.3 ng/g for the gamma-isomer. Concentrations of total HBCD ranged from <0.075 to 3.7 ng/g. Roughly two-thirds of HBCD profiles in suspended sediments were dominated by the gamma-isomer, and were similar to profiles of commercial technical mixtures. Profiles in the remaining samples were dominated by the alpha-isomer. The beta-isomer was consistently detected at substantially lower levels than the other isomers; this isomer is a minor constituent in the commercial technical mixtures. Seasonal sampling showed significant shifts in the relative ratios of the HBCD isomers. The spatial distribution of HBCD in the Detroit River was similar to other persistent organic pollutants (e.g., PCBs), and showed a strong association with urban/industrial activities in the watershed. However, the highest HBCD concentrations (2.6-3.7 ng/g) were associated with areas of contemporary industrial activity, and were much lower than maximum concentrations of PCBs (2.2 microg/g) found in areas of the Detroit River associated with historical industrial activity.     

Towards improved socio-economic assessments of ocean acidification’s impacts

Ocean acidification is increasingly recognized as a component of global change that could have a wide range of impacts on marine organisms, the ecosystems they live in, and the goods and services they provide humankind. Assessment of these potential socio-economic impacts requires integrated efforts between biologists, chemists, oceanographers, economists and social scientists. But because ocean acidification is a new research area, significant knowledge gaps are preventing economists from estimating its welfare impacts. For instance, economic data on the impact of ocean acidification on significant markets such as fisheries, aquaculture and tourism are very limited (if not non-existent), and non-market valuation studies on this topic are not yet available. Our paper summarizes the current understanding of future OA impacts and sets out what further information is required for economists to assess socio-economic impacts of ocean acidification. Our aim is to provide clear directions for multidisciplinary collaborative research.     

Identifying trophic variation in a marine suspension feeder: DNA- and stable isotope-based dietary analysis in Mytilus spp.

Accurate field data on trophic interactions for suspension feeders are lacking, and new approaches to dietary analysis are necessary. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was integrated with stable isotope analysis to examine dietary patterns in suspension-feeding Mytilus spp. from seven spatially discrete locations within a semi-enclosed marine bay (Strangford Lough, Northern Ireland) during June 2009. Results of the two methods were highly correlated, reflecting dietary variation in a similar manner. Variation in PCR-DGGE data was more strongly correlated with the principal environmental gradient (distance from the opening to the Irish Sea), while values of δ ¹³C and δ ¹⁵N became progressively enriched, suggesting a greater dependence on animal tissue and benthic microalgae. Diatoms and crustaceans were the most frequently observed phylotypes identified by sequencing, but specific DNA results provided little support for the trophic trends observed in the stable isotope data. This combined approach offers an increased level of trophic insight for suspension feeders and could be applied to other organisms.     

The deployment of an advanced gasification technology in the treatment of household and other waste streams

The Gasplasma^® process developed by APP is an advanced thermal conversion (ATC) technology which has been developed for the treatment of household and trade wastes and has also been successfully applied to the handling of wastes derived from landfill and would be capable of achieving effective energy conversion when utilised as an integrated part of the Enhanced Landfill Mining (ELFM) concept.The core Gasplasma^® technology comprises a two-stage thermal treatment system—firstly, a fluidizing bed gasifier which converts the wastes to a crude syngas using oxy-steam and, secondly, a plasma converter that efficiently cracks problematic tars in the raw syngas to produce a reformed and clean syngas suitable for generating electrical power in gas engines and also recovering an environmentally stable vitrified product for use as a secondary aggregate material. The utilization of oxy-steam as a gasifying agent greatly reduces the syngas volume compared to other ATC processes and incineration and hence reduces the cost of the gas cleaning system while improving the efficiency of the process. By adopting this two-stage approach, high energy conversion (74–90%) and carbon conversion (95 ± 1.6%) efficiencies were achieved with the Gasplasma^® plant that compare favourably with published efficiencies data. The calculated net exportable power generation efficiency for a commercial scale plant is significantly in excess of 25%. This compares well with the published figures of 17.7–23% for fluidized bed technologies processing MSW.     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

Soil arsenic surveys of New Orleans: localized hazards in children’s play areas

Arsenic (As) ranks first on the 2005 and 2007 hazardous substances priority lists compiled for the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). This study describes two New Orleans soil As surveys: (1) a survey of composite soil samples from 286 census tracts and (2) a field survey of soil As at 38 play areas associated with the presence of chromated-copper-arsenate (CCA)-treated wood on residential and public properties. The survey of metropolitan New Orleans soils revealed a median As content of 1.5 mg/kg (range <0.2–16.4) and no distinctive differences between the soils of the city core and outlying areas. Play area accessible soils associated with CCA-treated wood (N = 32) had a median As of 57 mg/kg and 78% of the samples were ≥12 mg/kg, the Louisiana soil As standard. The field survey of play areas for CCA-treated wood (N = 132 samples at 38 sites) was conducted with a portable energy-dispersive X-ray fluorescence (XRF) analyzer. Seventy-five of 132 wood samples (56.8%) were deemed CCA-treated wood. Of the 38 play areas surveyed, 14 (36.8%) had CCA-treated wood. A significant association (Fisher’s exact p-value = 0.348 × 10⁻⁶) was found between CCA-treated wood and soil As (N = 75). At one elementary school CCA-treated woodchips (As range 813–1,654 mg As/kg) covered the playgrounds. The situation in New Orleans probably exists in play areas across the nation. These findings support a precautionary program for testing soils and wood for hazardous substances at all play areas intended for children.     

Prenatal diagnosis of congenital non-bullous ichthyosiform erythroderma (lamellar ichthyosis)

We report the first positive prenatal diagnosis ofcongenital non-bullous ichthyosiform erythroderma or lamellar ichthyosis. Fetal skin samples were obtained by fetoscopy at 21 weeks' gestation and examined by light and electron microscopy. Light microscopy revealed a thickened interfollicular epidermis with multiple layers of flattened cells and excessive keratinization of the epidermal lining of the follicular infundibulum. Electron microscopy of the thickened epidermis revealed granular cells that contained larger-than-normal keratohyalin granules and multiple layers of parakeratotic cornified cells. Although there was regional variation in the degree of interfollicular keratinization, follicles from all regions showed greater and more complete keratinization, indicating that they express the abnormality early enough in development to permit prenatal diagnosis at about 20 weeks' gestation.