High precision during food recruitment of experienced (reactivated) foragers in the stingless bee<Emphasis Type="Italic"> Scaptotrigona mexicana</Emphasis> (Apidae,Meliponini)

Several studies have examined the existence of recruitment communication mechanisms in stingless bees. However, the spatial accuracy of location-specific recruitment has not been examined. Moreover, the location-specific recruitment of reactivated foragers, i.e., foragers that have previously experienced the same food source at a different location and time, has not been explicitly examined. However, such foragers may also play a significant role in colony foraging, particularly in small colonies. Here we report that reactivated Scaptotrigona mexicana foragers can recruit with high precision to a specific food location. The recruitment precision of reactivated foragers was evaluated by placing control feeders to the left and the right of the training feeder (direction-precision tests) and between the nest and the training feeder and beyond it (distance-precision tests). Reactivated foragers arrived at the correct location with high precision: 98.44% arrived at the training feeder in the direction trials (five-feeder fan-shaped array, accuracy of at least ±6° of azimuth at 50 m from the nest), and 88.62% arrived at the training feeder in the distance trials (five-feeder linear array, accuracy of at least ±5 m or ±10% at 50 m from the nest). Thus, S. mexicana reactivated foragers can find the indicated food source at a specific distance and direction with high precision, higher than that shown by honeybees, Apis mellifera, which do not communicate food location at such close distances to the nest.     

Foliar uptake and metal(loid) bioaccessibility in vegetables exposed to particulate matter

At the global scale, high concentrations of particulate matter (PM) enriched with metal(loid)s are currently observed in the atmosphere of urban areas. Foliar lead uptake was demonstrated for vegetables exposed to airborne PM. Our main objective here was to highlight the health risk associated with the consumption of vegetables exposed to foliar deposits of PM enriched with the various metal(loid)s frequently observed in the atmosphere of urban areas (Cd, Sb, Zn and Pb). Leaves of mature cabbage and spinach were exposed to manufactured mono-metallic oxide particles (CdO, Sb₂O₃ and ZnO) or to complex process PM mainly enriched with lead. Total and bioaccessible metal(loid) concentrations were then measured for polluted vegetables and the various PM used as sources. Finally, scanning electronic microscopy coupled with energy dispersive X-ray microanalysis was used to study PM–phyllosphere interactions. High quantities of Cd, Sb, Zn and Pb were taken up by the plant leaves. These levels depended on both the plant species and nature of the PM, highlighting the interest of acquiring data for different plants and sources of exposure in order to better identify and manage health risks. A maximum of 2 % of the leaf surfaces were covered with the PM. However, particles appeared to be enriched in stomatal openings, with up to 12 % of their area occupied. Metal(loid) bioaccessibility was significantly higher for vegetables compared to PM sources, certainly due to chemical speciation changes. Taken together, these results confirm the importance of taking atmospheric PM into account when assessing the health risks associated with ingestion of vegetables grown in urban vegetable crops or kitchen gardens.     

基于综合环境风险的砷污染场地优控筛选方法

污染场地的优控筛选是国家和地区污染场地管理的关键环节,有利于提高污染场地修复的高效性和经济性。研究以污染源强、污染途径脆弱性和受体敏感性作为筛选的主要因素,构建了基于综合环境风险的优控重金属污染场地筛选方法。通过调查某市15个砷渣污染场地,利用综合环境风险指数法分析区域不同污染场地的危害程度,据此推算不同污染场地危害 程度大小次序,并设置不同情景进行敏感性分析,从而筛选出某市优控砷渣污染场地名单。结果表明:污染场地H15和H12在不同权重情景下均处于高危害程度水平,为优控污染场地；H2在多数情景下危害程度较高,确定为备选优控污染场地。     

Effects of a sulfonylurea herbicide on the soil bacterial community

Sulfonylurea herbicides are widely used on a wide range of crops to control weeds. Chevalier® OnePass herbicide is a sulfonylurea herbicide intensively used on cereal crops in Algeria. No information is yet available about the biodegradation of this herbicide or about its effect on the bacterial community of the soil. In this study, we collected an untreated soil sample, and another sample was collected 1 month after treatment with the herbicide. Using a high-resolution melting DNA technique, we have shown that treatment with Chevalier® OnePass herbicide only slightly changed the composition of the whole bacterial community. Two hundred fifty-nine macroscopically different clones were isolated from the untreated and treated soil under both aerobic and microaerobic conditions. The strains were identified by sequencing a conserved fragment of the 16S rRNA gene. The phylogenetic trees constructed using the sequencing results confirmed that the bacterial populations were similar in the two soil samples. Species belonging to the Lysinibacillus, Bacillus, Pseudomonas, and Paenibacillus genera were the most abundant species found. Surprisingly, we found that among ten strains isolated from the treated soil, only six were resistant to the herbicide. Furthermore, bacterial overlay experiments showed that only one resistant strain (related to Stenotrophomonas maltophilia) allowed all the sensitive strains tested to grow in the presence of the herbicide. The other resistant strains allowed only certain sensitive strains to grow. On the basis of these results, we propose that there must be several biodegradation pathways for this sulfonylurea herbicide.     

Integration of toxicological and chemical tools to assess the bioavailability of metals and energetic compounds in contaminated soils

Bioavailability is critical for understanding effects that might result from exposure of biota to contaminated soils. Soils from military range and training areas (RTAs) are contaminated principally by energetic materials (EM) and metals. Their chemical characteristics are relatively well known and toxicity assessment of soils from RTAs are in some cases available. However, bioavailability on these sites needs to be comprehensively characterized. A holistic approach to bioavailability, incorporating both chemical and earthworm toxicological indicators, was applied to soils from an anti-tank firing range at a Canadian Forces Base. Results showed that HMX and the metals Zn, Pb, Bi and Cd, though not consistently the prevailing toxicants, were the most accessible to earthworms. Some metals (notably Cu, Zn, Cr and Bi) were also accumulated in earthworm tissue but those were not necessarily expected given their bioaccessibility (i.e., the chemical availability of contaminants in the environment for the organisms) at the beginning of the exposure. The tested soils impaired earthworm reproduction and reduced adult growth. Measurement of selected sublethal parameters indicated that lysosomal integrity (determined as the neutral red retention time--NRRT) was decreased, while elevated superoxide dismutase (SOD) activity suggested that earthworms experienced oxidative stress. The correspondence between the NRRT and metal contamination pattern suggested that metals may be the main cause of lysosomal disruption in EM-contaminated soils. The approach to bioavailability appraisal adopted in this case appears to be a promising practice for site-specific assessment of contaminated land.     

Dynamis CO2 quality recommendations

In the carbon capture and storage (CCS) chain, transport and storage set different requirements for the composition of the gas stream mainly containing carbon dioxide (CO₂). Currently, there is a lack of standards to define the required quality for CO₂ pipelines. This study investigates and recommends likely maximum allowable concentrations of impurities in the CO₂ for safe transportation in pipelines. The focus is on CO₂ streams from pre-combustion processes. Among the issues addressed are safety and toxicity limits, compression work, hydrate formation, corrosion and free water formation, including the cross-effect of H₂S and H₂O and of H₂O and CH₄.     

Between introgression events and fragmentation, islands are the last refuge for the American crocodile in Caribbean Mexico

Habitat loss and degradation in the Mexican Caribbean, caused by the development of tourism, have decreased the potential nesting area for the American crocodile (Crocodylus acutus) and have fragmented the populations of the Yucatan peninsula. Our study investigated five populations (three continental: North, South, Sian Ka’an, and two insular: Cozumel, Banco Chinchorro) of C. acutus in the Mexican Caribbean using seven different inter simple sequence repeat (ISSR) markers as tools for genetic variability and population differentiation. Three classification methods were tested and compared: distance analysis, self-organizing map, and Bayesian methods, to evaluate the resolution of each method with ISSR markers. The 77 loci selected revealed a high variability between populations (polymorphism from 17% for Sian Ka’an to 75% for Banco Chinchorro) with a total polymorphism of 84% and a global coefficient of gene differentiation (G _ST ) of 0.296, but low values of Nei’s Gene diversity (from 0.065 for Sian Ka’an to 0.233 for Banco Chinchorro). Our results suggest elevated inbreeding in all local populations with higher indices for Banco Chinchorro and lower indices for Sian Ka’an. Three independent classification methods gave similar results, and suggested that most continental individuals are admixtures, with different levels of introgression, with the sympatric species Crocodylus moreletii. We propose that the islands/atolls remain the sole areas with genetically “pure” American crocodiles and we discuss these results for future conservation of this endangered crocodile species.     

Plant growth rates and seed size: a re-evaluation

Small-seeded plant species are often reported to have high relative growth rate or RGR. However, because RGR declines as plants grow larger, small-seeded species could achieve higher RGR simply by virtue of their small size. In contrast, size-standardized growth rate or SGR factors out these size effects. Differences in SGR can thus only be due to differences in morphology, allocation, or physiology. We used nonlinear regression to calculate SGR for comparison with RGR for 10 groups of species spanning a wide range of life forms. We found that RGR was negatively correlated with seed mass in nearly all groups, but the relationship between SGR and seed mass was highly variable. We conclude that small-seeded species only sometimes possess additional adaptations for rapid growth over and above their general size advantage.     

Crossing the frontier: vertical transit rates of deep diving cormorants reveal depth zone of neutral buoyancy

Knowing the depth zone of neutral buoyancy of divers is important because buoyancy can determine how animals manage their energy budget. In this study, we estimate the depth zone of neutral buoyancy of free-ranging cormorants for the first time, using time-depth recorders. We discovered that vertical ascent rates of 12 Crozet and 15 Kerguelen diving blue-eyed shags (respectively Phalacrocorax melanogenis and P. verrucosus) slowed down considerably at the 50–60 m depth zone. We suggest this was due to birds trying to reach the surface from that point upwards using reduced locomotor activity because the force of buoyancy becomes greater than the force of gravity at that depth. The results show a shift of this depth zone in relation to maximum targeted dive depth, suggesting cormorants may control buoyancy through respiratory air volume adjustment. Interestingly, 60 m is close to the maximum depth zone reached by these two species during dives lasting 4 min, their estimated behavioural aerobic dive limit. This suggests that the decision to swim deeper has a direct consequence on the energy budget, with time spent recovering at the surface (time thus lost to foraging) strongly increasing relative to the preceding time of submergence. Resources found in deeper waters must be of sufficient quantity or quality to justify crossing the frontier of physical neutral buoyancy.     

Host selection by a kleptobiotic spider

Why do kleptobiotic spiders of the genus Argyrodes seem to be associated with spiders of the genus Nephila worldwide? Observations following introduction of experimental insect prey of different sizes and weights on to host webs revealed that: (1) small prey are more effectively retained on the web of Nephila clavipes than on the web of another common host, Leucauge venusta. (2) N. clavipes did not consume small prey that accumulated on the web whereas larger, heavier prey were enveloped and stored. (3) We observed clear partitioning of prey items between N. clavipes and Argyrodes spp.; diet selection by Argyrodes did not overlap with that of N. clavipes but closely overlapped with that of L. venusta. (4) L. venusta responds very quickly to prey impact whereas N. clavipes is slower, offering a temporal window of opportunity for Argyrodes foraging. (5) The ability of L. venusta to detect and respond to small items also means that it acts aggressively to Argyrodes spp., whereas N. clavipes does not. Consequently, food-acquisition behaviours of Argyrodes were clearly less risky with N. clavipes compared with L. venusta. We conclude that when a kleptobiotic organism has a choice of various host species, it will opt for the least risky host that presents the highest rate of availability of food items. The fact that Nephila species present such characteristics explains the worldwide association with Argyrodes kleptobiotic spiders.