Correlations and variance among species traits explain contrasting impacts of fragmentation and habitat loss on functional diversity

Landscape Ecology - Understanding how landscape fragmentation affects functional diversity, defined as the distribution of functional traits in an assemblage, is critical for managing landscapes...     

Occurrence of High In-Stream Nitrite Levels in a Temperate Region Agricultural Watershed

This study is the first to report nitrite occurrence and variability in surface water across an agricultural watershed in the province of Quebec, Canada. Nitrite (NO₂ ^?) concentrations were monitored across a 2.4 km² watershed during 2 years. Water samples were collected at the outlet from April to November and in three contrasted stream branches (six stations) during three hydrological regimes (summer low water levels, fall recharge, and snowmelt). Our study clearly demonstrates that NO₂ ^? levels observed at the outlet are not representative of NO₂ ^? variability across the micro-watershed. Surface water collected in cropped areas presents high NO₂ ^? concentrations during summer low water levels, often exceeding guidelines for aquatic life, with NO₂ ^? means ranging from 0.022 to 0.107 mg N L^?1 and maximum value reaching 0.156 mg N L^?1. Furthermore, the two stream branches in cropped area have demonstrated significant differences in NO₂ ^? concentrations and other water quality parameters. The importance of groundwater discharge to streams in the micro-watershed Bras d’Henri may potentially generate different in-stream sources of NO₂ ^? and water quality parameters. However, further studies are essential to determine sources and processes related to in-stream NO₂ ^? peaks.     

Influence of the allelic variants encoded at the Gli-B1 locus, responsible for a major allergen of wheat, on IgE reactivity for patients suffering from food allergy to wheat

Wheat presents an important genetic diversity that could be useful to look for cultivars with reduced allergencity. omega5-Gliadins have been described as major allergens for wheat allergic patients suffering from wheat-dependent exercise-induced anaphylaxis (WDEIA) and some cases of chronic urticaria (U). Our objective was to study the influence of genetic variability at the Gli-B1 locus encoding for omega5-gliadins on the reactivity of IgE antibodies from these patients. We selected cultivars expressing 13 alleles at Gli-B1 including a wheat/rye translocation and studied the reactivity to gliadins of a rabbit antiserum specific for omega5-gliadins and of IgE from 10 patients. The antiserum and IgE from nine patients with WDEIA and U strongly detected omega5-gliadins expressed by most of the Gli-B1 alleles but showed no or faint responses to the gliadins and secalins extracted from the translocated wheat. The selection of genotypes lacking the Gli-B1 locus may reduce wheat allergenicity.     

Proteome changes in leaves from grapevine (Vitis vinifera L.) transformed for alcohol dehydrogenase activity

A proteomic approach has been used to study changes in leaf protein content from plants transformed for alcohol dehydrogenase (ADH) activity. Individual quantitative analysis of 190-436 spots separated by two-dimensional electrophoresis was performed, and spots displaying significant quantitative changes between control (C), sense (S), and antisense (R) transformants were selected using Student's t test. Of the 14 spots selected and further analyzed after trypsic digestion, 9 could be identified by MS analysis and 5 by LC-MS/MS. Identified proteins had mainly a chloroplastic origin: four rubisco large subunits, one rubisco binding protein, two glutamine synthetases, one elongation factor Tu, one ATP synthase beta subunit, and one plastidic aldolase. Proteins with other localization were also identified, such as a UDP-glucose pyrophosphorylase, a mitochondrial aminomethyltransferase, a linalool synthase, which comigrated with the protein identified as elongation factor Tu, an enolase comigrating with a glyceraldehyde 3-phosphate dehydrogenase, and a mixture of eight proteins among which were a dehydroascorbate reductase, a chalcone isomerase, and a rubisco activase. The results emphasize the changes in carbon metabolism-associated proteins linked to the alteration in ADH activity of grapevine transformant leaves.     

Protective effects of 4-hydroxycinnamic ethyl ester derivatives and related dehydrodimers against oxidation of LDL: radical scavengers or metal chelators?

4-Hydroxycinnamate derivatives are known to be potent protectors against oxidation of low-density lipoproteins (LDL), via a combination of free radical scavenging and transition metal chelation. Through a series of 4-hydroxycinnamic ethyl ester derivatives and related 8-8 dehydrodimers, we have tried to bring out the structural requirements for radical scavenging and cupric ion chelation. We found that the monomeric compounds, except for highly lipophilic tert-butyl derivative 3, exhibited rather low radical scavenging properties. Furthermore, they did not chelate copper but, in contrast, reduced cupric ion to cuprous ion, affording the related 8-8 dehydrodimers, for which they could be considered as precursors in vitro. In the copper-dependent human LDL oxidation in vitro, the cyclic 8-8 dehydrodimer forms behaved essentially as efficient copper chelators, while related noncyclic 8-8 forms, which were found to be the best protectors, mainly acted as radical scavengers.     

Threshold effect of eucalypt density on an aggressive avian competitor

General guidelines available to revegetation planners focus on the spatial context and dimensions of the revegetated site. However, site-specific habitat factors can have overarching importance for habitat value, especially where interactions with competitors or predators may play an important role. Current revegetation projects in Australia which aim to restore slow-growing buloke (Allocasuarina luehmannii) woodland, a threatened habitat important for bird conservation, usually include faster-growing eucalypts in plantings. This research aimed to identify whether eucalypt presence in buloke woodland facilitates invasion by the noisy miner (Manorina melanocephala), an aggressive competitor that is absent from pure buloke woodland. Birds were surveyed in buloke woodland remnants that contained eucalypts as a sub-dominant species at densities of 0-16 per ha. The probability of noisy miner presence in buloke woodland increased markedly where eucalypts were present at a density of approximately five per hectare. The presence of noisy miners resulted in a substantial difference in bird assemblage structure and composition. Small-bodied insectivorous birds which are experiencing population declines in southern Australia were recorded on average six times more often in transects without noisy miners (low-eucalypt density transects). Avian behaviour and habitat use was also altered, with birds flying more frequently in transects where noisy miners were present. A minor difference in habitat composition results in substantial degradation of the conservation value of non-eucalypt woodland in eastern Australia due to invasion by aggressive avian competitors. Revegetation and restoration practices should take into account the potential for such subtle floristic differences to result in substantial variation in conservation outcomes.     

The influence of livestock grazing and weed invasion on habitat use by birds in grassy woodland remnants

Remnants of native vegetation in regions dominated by agriculture are subject to degradation, especially by livestock grazing and weed invasion. Ground-foraging birds are amongst the most threatened bird groups in Australia, and these agents of degradation might be contributing to their decline by causing a reduction in food availability. We studied the foraging behaviour and microhabitat use of seven species of ground-foraging insectivores in south-eastern Australian buloke woodland remnants with native, grazed and weedy ground-layers. If birds must resort to using more energetically expensive prey-attack manoeuvres, or selectively use substrates and microhabitats that are less available in degraded habitats, then such degradation is likely to be negatively impacting on these species. We found evidence of a negative impact of one or both of these types of degradation on five of the seven bird species. Three species that employ a range of foraging manoeuvres to attack prey used potentially more energetically expensive aerial manoeuvres significantly more frequently in weedy remnants than in remnants with a native or grazed ground layer. Red-capped robins Petroica goodenovii and brown treecreepers Climacteris picumnus both selectively foraged near trees in grazed sites, and hooded robins Melanodryas cucullata, red-capped robins and willie wagtails Rhipidura leucophrys avoided foraging in microhabitats with a high percentage cover of exotic grasses in weedy sites. Brown treecreepers were also less likely to be present in weedy sites that had been protected from grazing than in either grazed or native sites. These results suggest that although grazing appears to have a detrimental impact on foraging habitat of ground-foraging birds, the exclusion of livestock grazing from previously disturbed buloke remnants alone is not adequate to restore habitat values for ground-foraging birds. A conservation strategy for this habitat type should consider the exclusion of heavy grazing from sites with an intact cryptogamic crust and the management of weeds in disturbed remnants, potentially through the use of carefully controlled light grazing.     

Determination of methylmercury in fish by headspace-gas chromatography with microwave-induced-plasma detection

Some additional experiments checking out the extraction method recently developed for the determination of MeHg in biological samples by Headspace Gas Chromatography with Microwave Induced Plasma atomic emission spectroscopy detection were performed. In this method, the MeHg is cleaved from the biological tissue by H₂SO₄ and by addition of iodoacetic acid converted to the iodide form. These reaction steps take place in a closed headspace vial. The H₂SO₄ concentration and the sample matrix have an important influence on the recovery of the MeHg from the sample and these effects are discussed. The method was then applied to the determination of MeHg in cod fish caught in the North Sea. Levels found ranged from 0.13 to 0.63 μg g⁻¹ dw with a mean of 0.33 μg g⁻¹ on the 25 samples analyzed. The total Hg content of these samples was also determined by Cold Vapour Atomic Absorption Spectrometry, and all data pooled ranged from 0.19 to 0.90 μg g⁻¹ with a mean of 0.40 μg g⁻¹. A study of the ratio MeHg/total Hg revealed that MeHg always constituted more than 60 % of the total Hg level, with a mean of 83 % on the 25 samples. The percentage MeHg did not increase or decrease markedly when the total Hg content increased. It could be concluded that these North Sea samples are not much contaminated by Hg and are surely suitable for consumption.     

Host cell invasion by apicomplexan parasites: insights from the co-structure of AMA1 with a RON2 peptide

Apicomplexan parasites such as Toxoplasma gondii and Plasmodium species actively invade host cells through a moving junction (MJ) complex assembled at the parasite-host cell interface. MJ assembly is initiated by injection of parasite rhoptry neck proteins (RONs) into the host cell, where RON2 spans the membrane and functions as a receptor for apical membrane antigen 1 (AMA1) on the parasite. We have determined the structure of TgAMA1 complexed with a RON2 peptide at 1.95 angstrom resolution. A stepwise assembly mechanism results in an extensive buried surface area, enabling the MJ complex to resist the mechanical forces encountered during host cell invasion. Besides providing insights into host cell invasion by apicomplexan parasites, the structure offers a basis for designing therapeutics targeting these global pathogens.