A workflow to investigate the impacts of weathered multi-walled carbon nanotubes to the mud snail Lymnaea stagnalis

Environmental Science and Pollution Research - Although the development and application of nanomaterials is a growing industry, little data is available on the ecotoxicological effects on aquatic...     

Do resources or natural enemies drive bee population dynamics in fragmented habitats?

The relative importance of bottom-up or top-down forces has been mainly studied for herbivores but rarely for pollinators. Habitat fragmentation might change driving forces of population dynamics by reducing the area of resource-providing habitats, disrupting habitat connectivity, and affecting natural enemies more than their host species. We studied spatial and temporal population dynamics of the solitary bee Osmia rufa (Hymenoptera: Megachilidae) in 30 fragmented orchard meadows ranging in size from 0.08 to 5.8 ha in an agricultural landscape in central Germany. From 1998 to 2003, we monitored local bee population size, rate of parasitism, and rate of larval and pupal mortality in reed trap nests as an accessible and standardized nesting resource. Experimentally enhanced nest site availability resulted in a steady increase of mean local population size from 80 to 2740 brood cells between 1998 and 2002. Population size and species richness of natural enemies increased with habitat area, whereas rate of parasitism and mortality only varied among years. Inverse density-dependent parasitism in three study years with highest population size suggests rather destabilizing instead of regulating effects of top-down forces. Accordingly, an analysis of independent time series showed on average a negative impact of population size on population growth rates but provides no support for top-down regulation by natural enemies. We conclude that population dynamics of O. rufa are mainly driven by bottom-up forces, primarily nest site availability.     

Rapid tissue reduction and recovery in the sponge <Emphasis Type="Italic">Aplysinella</Emphasis> sp.

We observed a pronounced, yet reversible tissue reduction in the tropical sponge Aplysinella sp. under non-experimental conditions in its natural habitat, after transfer into seawater tanks, as well as after transplantation from deep to shallow water in the field. Tissue reduction resulted in the formation of small “reduction bodies” tightly attached to the sponge skeleton. Although volume loss and gain were substantial, both tissue reduction and regeneration were often remarkably rapid, occurring within few hours. Microscopic analysis of the reduction bodies revealed morphological similarities to previously described sponge primmorphs, with densely packed archaeocytes and spherulous cells enclosed by a thin layer of epithelial-like cells. Denaturing gradient gel electrophoresis (DGGE) revealed pronounced changes in the sponge-associated microbial community upon tissue reduction during laboratory and field experiments and following changes in ambient conditions after transplantation in the field. Generally, the microbial community associated with this sponge proved less stable, less abundant, and less diverse than those of other, previously investigated Verongid sponges. However, one single phylotype was consistently present in DGGE profiles of Aplysinella sp. This phylotype clustered with γ-proteobacterial sequences found previously in other sponge species of different taxonomic affiliations and geographic provenances, as well as in sponge larvae. No apparent changes in the total secondary metabolite content (per dry weight) occurred in Aplysinella sp. upon tissue reduction; however, comparative analysis of intact and reduced tissue suggested changes in the concentrations of two minor compounds. Besides being ecologically interesting, the tissue reduction phenomenon in Aplysinella sp. provides an experimentally manipulable system for studies on sponge/microbe symbioses. Moreover, it may prove useful as a model system to investigate molecular mechanisms of basic Metazoan traits in vivo, complementing the in vitro sponge primmorph system currently used in this context.     

An individual-based model to study the reproduction of egg bearing copepods: Application to Eurytemora affinis (Copepoda Calanoida) from the Seine estuary,France

Limited empirical studies have elucidated the daily egg production and associated reproductive processes of egg bearing copepod. Herein, we present an individual-based model which constitutes a realistic representation of the reproduction in egg bearing copepods. The model has been parameterized using an extensive set of experimental data obtained from the literature and from the laboratory and field experiments on the estuarine copepod Eurytemora affinis. The proposed model takes into account the adult female longevity, the clutch size and interclutch duration, which is a function of egg maturation time and latency time required by the female after egg hatching to produce a new clutch. The embryonic development time and hatching success are also taken into account. The effect of temperature on the means and variances of above-mentioned reproductive parameters has been also incorporated. A multi agent system based generic platform “Mobidyc” has been used to generate and calibrate the model. The model demonstrates the reproductive parameters of females of E. affinis which is validated through individual based experiments. Temperature specific simulations provide a dynamical explanation of temperature effect on the cumulative egg production. The daily survival principally affects the number of clutches produced per female during its life span. The results obtained in the present study by combining temperature and survival effects reveal the relatively greater importance of the first factor on the daily egg production of egg-carrying copepods. The present model is generic and hence easily applicable to other animals with comparable reproductive strategy.     

Chemical composition and pheromonal function of the defensive secretions in the subtribe Stizopina (Coleptera, Tenebrionidae, Opatrini)

The chemical composition of the defensive secretions of 52 species from 15 genera of the tenebrionid subtribe Stizopina was analyzed. The secretions of all species contained 1,4-benzoquinones, 1-alkenes, and monoterpene hydrocarbons, only one species was lacking the latter. Methyl- and ethyl-1,4-benzoquinone were ubiquitous, mostly accompanied by smaller amounts of 1,4-benzoquinone as well as isopropyl- and propyl-1,4-benzoquinone. 1-Alkenes were dominated by 1-undecene with varying admixtures of other 1-alkenes. The monoterpene hydrocarbons always consisted of a mixture of α-pinene, camphene, β-pinene and limonene, but also p-cymene, α-terpinene or α-phellandrene were found in some species. Furthermore, some species synthesized additional compounds such as phenols, ketones, 2,5-dihydroxy-6-methylbenzoate, 2-hydroxy-4-methoxyacetophenone and naphthoquinones. Bioassays showed that the defensive secretion co-functioned as an aggregation pheromone in the subtribe Stizopina. All nine tested species from six genera were attracted to defensive secretion of Stizopina species, but they did not distinguish between defensive secretions of different Stizopina species. This lack of discrimination might be the initial step for the formation of interspecific aggregations and the evolution of cleptoparasitism within the Stizopina.     

Ansätze zur regionalen Quantifizierung von Methan aus Pflanzen

Background

Methane as a gas influencing our climate is of high importance according to the Kyoto-Protocol. The more precisely we can determine anthropogenic and biogenic sources, the more effective measures we can take to reduce the gas. Direct emission of methane from plants apparently contributes significantly to the total emission but has not been accounted for in emission balances until now.

Methods

A model was created to calculate methane emission for a short time period in regional resolution for Lower Austria and to relate the results to known literature.

Results and Discussion

First model results suggest that the amount of methane released from plants in relation to emissions from other known sources are of importance.

Perspectives

The uncertainties associated with both measurements and quantification require reduction by further research.     

Role of sampling for crop-loss assessment and nematode management

Reliable sampling of nematode communities in crop-loss assessment provides basic characterization of the population dynamics and damage potential of given species in a particular host—cultivar environment. Loss assessments for annual plants may be based on samples taken at: (1) time of planting; (2) mid-season (where nematicide or resistant-cultivar treatments are used); and (3) at harvest. Population levels at, or shortly after, harvest are most useful in projecting nematode hazards for a subsequent crop, especially where survival rates are known. Root symptoms, root-gall or root-necrosis indices, taken at mid-season or at harvest also can be correlated with yield losses caused by Meloidogyne spp. and associated fungi. A composite sample of 20 to 50 soil cores (2.5 cm diameter × 20 cm deep) collected in a stratified or systematic pattern over a 1- to 2-ha area provides nematode population estimates within about 30–50% of the mean. The major problems encountered in relating these estimates to potential hazards and eventual crop losses are related to the striking variation in crop-nematode responses as influenced by environment, cultivar, and general crop-management practices. Relative precision in crop-loss assessment should be improved as more research on crop-nematode responses and sampling methodology is completed.     

Alterations in cytometric characteristics of hemocytes from the American oyster Crassostrea virginica exposed to a polycyclic aromatic hydrocarbon (PAH) contaminated environment

The effects of residing in a polycyclic aromatic hydrocarbon (PAH) contaminated environment on the cytometric characteristics of hemocytes from the American oyster Crassostrea virginica (collected from the Rappahannock River, Virginia, USA in Spring 1991) were analyzed using a multichannel Coulter counter (10000 hemocytes oyster^-1). The percentage and relative volume of small-sized hemocytes (>2.5 to 5.1 m) was higher (P<0.01) in oysters from Hospital Point (HP, a PAH contaminated site) in the Elizabeth River (ER), Virginia, compared to oysters from the relatively unpolluted Rappahannock River (RR). On the contrary, a decrease (P<0.001) in the percentage and volume of larger hemocytes (>6.2 to 10 m) was observed in the HP-oysters. Maintaining the RR-oysters at the HP site for 8 wk induced statistically significant increases in the number and relative volume contribution of the >2.5 to 5.1 m hemocytes and sharp decreases in the occurrence and relative volume of >6.2 to 13 m cells (P<0.01). By depurating the HP-oysters in the York River (the control site), the number of, and volume contributed by the small hemocytes (>2.5 to 5.1 m) showed a significant decrease over time as compared to the baseline values. On the other hand, the relative number of >6.2 to 13 m hemocytes increased sharply within 8 wk (P<0.001). This indicates that these changes are both inducible and reversible and, at least in part, due to exposure to the ER-sediment. Based on these studies, oyster hemocyte cytometric characteristics could be developed as a sensitive biomarker of exposure to PAH.     

Assessing the Vulnerability of Coastal Communities to Extreme Storms: The Case of Revere,MA., USA

Climate change may affect the frequency, intensity, and geographic distribution of severe coastal storms. Concurrent sea-level rise would raise the baseline of flooding during such events. Meanwhile, social vulnerability factors such as poverty and disability hinder the ability to cope with storms and storm damage. While physical changes are likely to remain scientifically uncertain into the foreseeable future, the ability to mitigate potential impacts from coastal flooding may be fostered by better understanding the interplay of social and physical factors that produce human vulnerability. This study does so by integrating the classic causal model of hazards with social, environmental, and spatial dynamics that lead to the differential ability of people to cope with hazards. It uses Census data, factor analysis, data envelopment analysis, and floodplain maps to understand the compound social and physical vulnerability of coastal residents in the city of Revere, MA, USA. This revised version was published online in August 2006 with corrections to the Cover Date.