Temporal variability of airborne bacterial community structure in an urban area

Temporal airborne bacterial genetic community structure and meteorological factors were analysed above an urban area in the northwest of France from December 2003 to April 2004 with a sampling strategy considering different time intervals (from an hour to a month). Principal component analysis (PCA) of B-ARISA (Bacterial-Automated Ribosomal Intergenic Spacer Analysis) profiles revealed a hierarchy in the temporal variability of bacterial community: daily<weekly<seasonal. Co-inertia analysis between B-ARISA data and meteorological factors demonstrated the correlation between the seasonal variability in the bacterial community and climatic conditions such as temperature and relative humidity, whereas daily and weekly variability seemed likely to be managed by other factors such as anthropogenic activities.     

Sonar backscatter differentiation of dominant macrohabitat types in a hydrothermal vent field.

Over the past 20 years, sonar remote sensing has opened ways of acquiring new spatial information on seafloor habitat and ecosystem properties. While some researchers are presently working to improve sonar methods so that broad-scale high-definition surveys can be effectively conducted for management purposes, others are trying to use these surveying techniques in more local areas. Because ecosystem management is scale-dependent, there is a need to acquire spatiotemporal knowledge over various scales to bridge the gap between already-acquired point-source data and information available at broader scales. Using a 675-kHz single-pencil-beam sonar mounted on the remotely operated vehicle ROPOS, 2200 m deep on the Juan de Fuca Ridge, East Pacific Rise, five dominant habitat types located in a hydrothermal vent field were identified and characterized by their sonar signatures. The data, collected at different altitudes from 1 to 10 m above the seafloor, were depth-normalized. We compared three ways of handling the echoes embedded in the backscatters to detect and differentiate the five habitat types; we examined the influence of footprint size on the discrimination capacity of the three methods; and we identified key variables, derived from echoes that characterize each habitat type. The first method used a set of variables describing echo shapes, and the second method used as variables the power intensity values found within the echoes, whereas the last method combined all these variables. Canonical discriminant analysis was used to discriminate among the five habitat types using the three methods. The discriminant models were constructed using 70% of the data while the remaining 30% were used for validation. The results showed that footprints 20-30 cm in diameter included a sufficient amount of spatial variation to make the sonar signatures sensitive to the habitat types, producing on average 82% correct classification. Smaller footprints produced lower percentages of correct classification; instead of the habitat types, the sonar data responded to intrapatch roughness and hardness characteristics. The sonar variables used in this study and the methods for extracting and transforming them are fully described in this paper and available in the public domain.     

Degradation of Polyethylene Designed for Agricultural Purposes

For many years now, scientific articles have been published on the potential biodegradability of polyethylene. Polyethylene (PE) with peroxidant additives, in the form of agricultural films, is sold by various suppliers as biodegradable mulch. Even though, the photo-chemical and thermal degradation of these products under artificial laboratory conditions is highlighted, several extrapolation on the biodegradation and, moreover, on the neutral environmental impact of PE are made. In this study, three different commercial mulch films have been submitted to standardised biodegradation tests and the results are discussed. The first conclusions are that a very low degree of biodegradation of the commercial PE films is achieved from these tests and that crosslinked PE micro-fragments are found in soil after a very long period of time.     

Anchovy (<Emphasis Type="Italic">Engraulis encrasicolus</Emphasis>) egg density measurements in the Bay of Biscay: evidence for the spatial variation in egg density with sea surface salinity

Knowledge of the pelagic vertical distribution of fish eggs is central for several aspects of fisheries science including fisheries recruitment and egg production studies. In modelling egg vertical distributions, variation in fish egg density is an important issue. Though variation in egg density between individual eggs has been reported, evidence for significant spatial variation in egg density is novel. The present study provides evidence that egg density of anchovy (Engraulis encrasicolus) varies spatially across spawning sites in the Bay of Biscay, depending on the regional scale variation in sea water properties due to river discharge. We measured the density of the eggs using a density gradient column at 17 stations in 2005 and 2006 as well as their diameter. At station, the variability in the individual egg density was statistically distributed according to a Gaussian probability function. Significant variation in the mean egg density was observed across stations. Mean egg density displayed a significant correlation with sea surface salinity. Results are discussed in light of the mechanisms determining the egg density.     

Effect of the endectocide ivermectin on filamentous fungi

We investigated the effect of ivermectin, at environmental concentrations and above, on several strains of filamentous fungi. Ivermectin did not show significant short-term effect on biomass production and germination rate of the spores. By contrast, the spore production was stimulated twofold in Phanerochaete chrysosporium and Mucor racemosus cultures, whereas that endpoint was reduced in Fusarium cultures. A long-term exposure of F. oxysporum to ivermectin reduced both production and germination of fungal spores. Ivermectin was not an inducer of exocellular oxidases.     

Effects of within- and among-patch experiences on the patch-leaving decision rules in an insect parasitoid

The present study aimed to address how an insect parasitoid makes patch-departure decisions from various types of host patches and how previous patch experiences in the environment modify this decision-making process. Experiments were done with the parasitic wasp Aphidius rhopalosiphi attacking the grain aphid Sitobion avenae. In the experiments, wasps were observed in a laboratory environment containing several patches of various host densities, and behavioural records were analysed using a Coxs proportional hazards model. Consideration of the effect of the within-patch experience gave a classic pattern of patch-leaving decision rules in parasitoids: A. rhopalosiphi used local information on host quality (i.e. numbers of ovipositions or rejections) and availability (i.e. patch density) to determine departure decision. However, consideration of previous patch experiences provided evidence that these departure rules are fundamentally dynamic, responding to the physiological state of the animal and the information it has about its environment. Results showed that A. rhopalosiphi decreased its tendency to leave the visited patch after an oviposition. However, when a female has already laid several other eggs in the environment, such an incremental mechanism gradually switched to a decremental one. Hence, A. rhopalosiphi responded to egg-load depletion by leaving the visited patches sooner and by depositing a smaller number of eggs in those patches, which probably led to a decreased level of superparasitism. Results also indicated that previous experiences enabled wasps to estimate spatial host distribution and then to adjust their behavioural decisions accordingly. Thus, A. rhopalosiphi was shown to adjust its patch residence time according to the quality and the number of the patches previously visited. These proximate mechanistic rules adopted by A. rhopalosiphi females are discussed in the context of general predictions from optimality models.Communicated by D. Gwynne     

Alkanes and hopanes for pollution source apportionment in coking plant soils

Polluted soils of former coking plants are characterized by multiple organic contributions, e.g. coal tar, coal, coke, soot, and natural organic matter, that can either be sources of polycyclic aromatic hydrocarbons (PAHs) or act as sorption surfaces for pollutants. The contamination level is usually based on the quantification of 16 PAHs but it does not provide any information on PAH sources. We studied the aliphatic fractions of 25 soil samples from a former coking plant site by microscopy and gas chromatography-mass spectrometry (GC-MS). The microscopic investigation allowed to identify four main organic contributions: coal tar, coal, coke, and natural organic matter. These isolated sources were analyzed and considered as reference materials. Although the PAH distributions were very similar in the 25 contaminated soils, alkanes and hopanes distributions were representative from various contributions characterizing the relative enrichment in coal, coal tars, or natural organic matter. Two principal component analyses based on n-alkanes and hopanes showed that three molecular indices, the carbon preference index, the low molecular weight/high molecular weight n-alkanes ratio, and the 18α(H)-22,29,30-trisnorhopane/(18α(H)-22,29,30-trisnorhopane+17α(H)-22,29,30-trisnorhopane) ratio allow to classify polluted soils according to various organic contributions.     

Scent of a nest: discrimination of own-nest odours in Antarctic prions,<Emphasis Type="Italic"> Pachyptila desolata</Emphasis>

Petrels and albatrosses evolved well-developed olfactory anatomical structures comparable to those of mammals. To date it has been demonstrated that petrels are attracted by food-related odours, and that some hypogean species have decreased homing performances if anosmic. The ability to distinguish between familiar and unfamiliar odours had not been demonstrated. Here we show that the Antarctic prion, Pachyptila desolata, is able to distinguish between its own nest and that of a conspecific, relying on olfactory cues only. When tested in a maze, only prions with an intact sense of smell made a choice and recognized their own burrow whereas anosmic birds did not. In the absence of leading odours in the maze prions behaved similarly to anosmic birds. These results suggest the mechanism used in the short-range homing process of this species as an olfactory beaconing and suggest the skill of recognising individually distinctive odours. Evolving an efficient identification system in the dark allowed these hypogean petrels to return to their colony at night and recognise their own burrow without singing. This behaviour protects them from predation by skuas, Catharacta skua lönnbergi, that hunt petrels by vision and hearing.