Contamination Expérimentale In Vivo et In Vitro par Aggregata eberthi: Etude Ultrastructurale1

The mechanism of host invasion by Aggregata has been experimentally investigated both in vivo (in the crab), and in vitro (in mollusc cell cultures) and followed by electron microscopy. A few hours after the infesting meal, sporozoites escaped from sporocysts in the crab stomach: then they reached the small intestine. There, they pussed through the epithelium, making their way between the cells. Perforation of the thick basal lamina was induced by means of the elaboration of a dense product, probably an enzyme. Sporozoites stretched themselves passing through the basal lamina and entered the connective tissue surrounding the digestive tract. Damages inflicted on the host were minimal. In vitro, merozoites were able to enter cells from several molluscs by penetrating the cell's plasmalemma. A nucleolus appeared in the nuclei of intracellular merozoites.     

Nitrogen Mobilization from Stubble and Roots during Re-growth of Defoliated Perennial Ryegrass

Nitrogen re-mobilization during ryegrass (Lolium perenne L.)re-growth was studied as a function of time. Roots and stubblecompounds were labelled with ¹⁵N before clipping. Experimentalresults clearly showed that ryegrass re-growth involves twoperiods of differing physiological significance. The first occursduring the first 6 d when nearly all the nitrogen of the newleaves comes from organic nitrogen re-mobilized from roots andstubble. At the same time, the uptake of nitrogen from the mediumis very low, no reduction of endogenous nitrate occurs and proteolysisand amino amido nitrogen re-mobilization in stubble are notfully compensated for by synthesis.Thus, the change in protein-Ncontent, expressed per plant, in stubble decreases from 998µg (uncut plant) to 866 µg and 661 µg for2 d and 4 d respectively after cutting. The second period (afterthe sixth day) may be more representative of stable behaviourof ryegrass, with assimilation of mineral nitrogen from themedium providing the predominant source of nitrogen for re-growth. Key words: Lolium perenne L., nitrogen, re-growth     

Five polymorphic microsatellite markers for the study of Cardiocondyla elegans (Hymenoptera: Myrmicinae)

We describe primer sequences for five microsatellite markers in Cardiocondyla elegans, an ant species with ergatoid males. Polymorphism of these loci was investigated using 236 individuals from 22 colonies from four locations. The microsatellites are dinucleotide repeats with four to 16 alleles, and the observed heterozygosity ranges from 0.244 to 0.720. We characterized these markers for the study of the population as well as the social structure of colonies.     

Functional diversity decreases with temperature in high elevation ant fauna

相似文献   

Metabolome and water status phenotyping of Arabidopsis under abiotic stress cues reveals new insight into ESK1 function

Metabolomic investigation of the freezing-tolerant Arabidopsis mutant esk1 revealed large alterations in polar metabolite content in roots and shoots. Stress metabolic markers were found to be among the most significant metabolic markers associated with the mutation, but also compounds related to growth regulation or nutrition. The metabolic phenotype of esk1 was also compared to that of wild type (WT) under various environmental constraints, namely cold, salinity and dehydration. The mutant was shown to express constitutively a subset of metabolic responses which fits with the core of stress metabolic responses in the WT. But remarkably, the most specific metabolic responses to cold acclimation were not phenocopied by esk1 mutation and remained fully inducible in the mutant at low temperature. Under salt stress, esk1 accumulated lower amounts of Na⁺ in leaves than the WT, and under dehydration stress its metabolic profile and osmotic potential were only slightly impacted. These phenotypes are consistent with the hypothesis of an altered water status in esk1 , which actually exhibited basic lower water content (WC) and transpiration rate (TR) than the WT. Taken together, the results suggest that ESK1 does not function as a specific cold acclimation gene, but could rather be involved in water homeostasis.     

Climate change, diapause termination and zooplankton population dynamics: an experimental and modelling approach

1. Earlier spring warming as predicted for climate change will alter combinations of water temperature and photoperiod that act as emergence cues for zooplankton resting stages. As a result, water temperature cue thresholds will be experienced at shorter photoperiods, a variable independent of weather variations. Also, light intensity, another potentially important cue for zooplankton emergence, could decrease in many lakes if symptoms of climate change resemble those of eutrophication. 2. We designed a laboratory experiment to test the effects of three factors, temperature (6, 9 and 12 °C), photoperiod (13L : 11D and 16L : 8D) and light intensity (20 and 35 μE m⁻² s⁻¹) on hatchling abundance and timing of hatching of daphniids (Daphnia ambigua) and rotifers (Keratella spp. and Synchaeta pectinata) from resting eggs. Further, we investigated the implications of potential changes in hatching dynamics, following variations in hatching cues, on zooplankton spring population development using predator–prey simulation models. 3. For hatchling abundance and timing of hatching, photoperiod had a significant effect for D. ambigua but not rotifers. Daphnia ambigua hatchling abundance decreased by 50% when incubated at conditions mimicking early spring (12 °C + 13‐h photoperiod) compared to a later spring (12 °C + 16‐h photoperiod). Light intensity has a significant effect only for S. pectinata, producing greater hatchling abundance at lower light intensity. 4. Simulation models suggest that in contrast to a later spring, an early warming produces a shift in spring zooplankton community composition, from daphniid to rotifer dominance. These patterns are primarily driven by differential zooplankton emergence response with variations in temperature–photoperiod cues. 5. Overall, our laboratory experiments and simulation models suggest that lakes with strong dependence on the ‘resting egg‐bank’, characteristic of many shallow north‐temperate lakes or in years with low winter survivorship of adult zooplankton, may be most susceptible to climate change. Further, fewer large grazers such as daphniids with an earlier spring may result in less control of cyanobacterial blooms in eutrophic lakes.     

Bacterial rhamnolipids are novel MAMPs conferring resistance to Botrytis cinerea in grapevine

Rhamnolipids produced by the bacteria Pseudomonas aeruginosa are known as very efficient biosurfactant molecules. They are used for a wide range of industrial applications, especially in food, cosmetics and pharmaceutical formulations as well as in bioremediation of pollutants. In this paper, the role of rhamnolipids as novel molecules triggering defence responses and protection against the fungus Botrytis cinerea in grapevine is presented. The effect of rhamnolipids was assessed in grapevine using cell suspension cultures and vitro-plantlets. Ca²⁺ influx, mitogen-activated protein kinase activation and reactive oxygen species production form part of early signalling events leading from perception of rhamnolipids to the induction of plant defences that include expression of a wide range of defence genes and a hypersensitive response (HR)-like response. In addition, rhamnolipids potentiated defence responses induced by the chitosan elicitor and by the culture filtrate of B. cinerea . We also demonstrated that rhamnolipids have direct antifungal properties by inhibiting spore germination and mycelium growth of B. cinerea . Ultimately, rhamnolipids efficiently protected grapevine against the fungus. We propose that rhamnolipids are acting as microbe-associated molecular patterns (MAMPs) in grapevine and that the combination of rhamnolipid effects could participate in grapevine protection against grey mould disease.     

Ecologically heterogeneous populations of the invasive ant Wasmannia auropunctata within its native and introduced ranges

Abstract 1. The biology of most invasive species in their native geographical areas remains largely unknown. Such studies are, however, crucial in shedding light on the ecological and evolutionary processes underlying biological invasions. 2. The present study focuses on the little fire ant Wasmannia auropunctata, a species native to Central and South America that has been widely introduced and which has become invasive throughout the tropics. We characterise and compare several ecological traits of native populations in French Guiana with those in one of its introduced ranges, New Caledonia. 3. We found ecologically heterogeneous populations of W. auropunctata coexisting in the species’ native geographical area. First, we found populations restricted to naturally perturbed areas (particularly floodplains) within the primary forest, and absent from the surrounding forest areas. These populations were characterised by low nest and worker densities. Second, we found dominant populations in recent anthropogenic areas (e.g. secondary forest or forest edge along road) characterised by high nest and worker densities, and associated with low ant species richness. The local dominance of W. auropunctata in such areas can be due to the displacement of other species (cause) or the filling‐up of empty habitats unsuitable to other ants (effect). With respect to their demographic features and ant species richness, the populations of native anthropogenic habitats were to a large extent similar to the invasive populations introduced into remote areas. 4. The results point to the need for greater research efforts to better understand the ecological and demographic features of invasive species within their native ranges.     

Fluctuating asymmetry in bank vole populations (Rodentia, Arvicolinae) reflects stress caused by landscape fragmentation in the Mont-Saint-Michel Bay

In intensively farmed, reclaimed areas (polders) of Mont-St-Michel Bay, France, bank voles ( Clethrionomys glareolus ) live in fragmented hedgerows, where populations are small and dispersal rates and genetic diversity are low. These small populations are likely to have been exposed to potential environmental and/or genetic stress. The sensitivity of development to stress can be measured by fluctuating asymmetry (FA). FA was calculated for three samples from a disturbed area and one sample from an adjacent, more connected and undisturbed landscape. Size FA was estimated from 16 measurements of the skull and teeth whilst shape asymmetry was estimated from the skull alone. Bank voles in fragmented hedgerows of the disturbed area had a higher degree of FA than bank voles from the more extensive and more connected hedges of the undisturbed area. These results were confirmed by the study of shape asymmetry, body mass and centroid size of the skull. There were no differences in FA between the three disturbed area samples. We conclude that FA does not reveal differences in the development of bank voles living in isolation under different local conditions in the various parts of the disturbed area. However, FA may allow differentiation between populations from greatly contrasting landscapes.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80, 37–44.