Why are anopheline mosquitoes not present in the Seychelles?

<p>Abstract</p> <p>Background</p> <p>Species of anopheline mosquitoes are largely distributed over emerged lands around the world and, within the tropics, few areas are without these insects, which are vectors of malaria parasites. Among the exceptions is the Seychelles archipelago in the western Indian Ocean. However, in the Aldabra island group, located in the extreme western portion of the archipelago, <it>Anopheles gambiae s.l. </it>was introduced, leading to massive proliferation and then elimination, with the most recent autochthonous malaria cases recorded in 1931.</p> <p>Methods</p> <p>In order to re-examine the absence of anopheline mosquitoes in the Seychelles, an entomological field survey was conducted in December 2008 at 17 sites on four granitic islands, including Mahé and Praslin, and ten sites on coralline atolls in the extreme west, including Aldabra.</p> <p>Results</p> <p>No evidence of larval or adult anophelines was found at the surveyed sites, which supports their absence in the Seychelles.</p> <p>Conclusions</p> <p>In the granitic islands of the Seychelles, the climate is favourable for anophelines. However, these islands are protected by their remoteness and prevailing seasonal winds. In addition, stagnant freshwater, required in anopheline larval development, is relatively uncommon on the granitic islands because of the steep slopes. In the southwestern atolls (Aldabra and Providence-Farquhar groups), the presence of a long dry season of up to nine months and the total absence of permanent natural freshwater prevents the breeding of anophelines and their successful colonization. The Seychelles does not have any native land mammals and like in other parts of the world (Antarctica, Iceland, New Caledonia, Central Pacific islands) their absence is associated with the lack of anophelines. This suggests an obligatory relationship for anophelines to feed on terrestrial mammals, without alternative for blood-feeding sources, such as bats, birds and reptiles.</p

Effect of a Dual Task on Postural Control in Dyslexic Children

Several studies have examined postural control in dyslexic children; however, their results were inconclusive. This study investigated the effect of a dual task on postural stability in dyslexic children. Eighteen dyslexic children (mean age 10.3±1.2 years) were compared with eighteen non-dyslexic children of similar age. Postural stability was recorded with a platform (TechnoConcept®) while the child, in separate sessions, made reflex horizontal and vertical saccades of 10° of amplitude, and read a text silently. We measured the surface and the mean speed of the center of pressure (CoP). Reading performance was assessed by counting the number of words read during postural measures. Both groups of children were more stable while performing saccades than while reading a text. Furthermore, dyslexic children were significantly more unstable than non-dyslexic children, especially during the reading task. Finally, the number of words read by dyslexic children was significantly lower than that of non-dyslexic children and, in contrast to the non-dyslexic children. In line with the U-shaped non-linear interaction model, we suggest that the attention consumed by the reading task could be responsible for the loss of postural control in both groups of children. The postural instability observed in dyslexic children supports the hypothesis that such children have a lack of integration of multiple sensorimotor inputs

Dynamic behaviour of benthic microalgal biomass in intertidal mudflats

International audienceThe dynamic behaviour of microphytobenthic biomass in a European intertidal mudflat has been analysed by comparing field and laboratory measurements. In an experimental mesocosm, where the effects of grazing by deposit-feeders and resuspension by tides had been significantly decreased, the benthic microalgal biomass followed a logistic-type growth curve, and thus converged towards a maximum value at which production is theoretically equal to zero. In the field, the kinetics of microalgal biomass—measured during 14 consecutive days at the beginning and at the end of every daytime exposures—exhibited a different pattern with biomass increases during daytime exposures and biomass decreases during the other periods, thus describing a series of oscillations. It is suggested that in the field, the effect of grazing and resuspension prevents biomass from holding steady at its maximum level. Moreover, it has been found a significant negative relationship which states that the higher the biomass level at the beginning of daytime exposures, the lower the net production during that daytime exposure. In other words, it turned out that in the field, the biomass also tends to converge towards a “field maximum” where net production is equal to zero. Taken together, these observations allow to hypothesize that the high productivity of the microphytobenthic community in intertidal mudflats is due to the tight coupling between physical and biological processes

Food sources of an infaunal suspension-feeding bivalve <I>Cerastoderma edule</I> in a muddy sandflat of Marennes-Oléron Bay, as determined by analyses of carbon and nitrogen stable isotopes

International audienceStable carbon and nitrogen isotope ratios were used to define the trophic base of the infaunal suspension-feeding bivalve Cerastoderma edule (L.) living on an intertidal muddy sandflat in Marennes-Oléron Bay, France. Suspended particulate organic matter (POM) collected from adjacent marine channels had a mean δ13C value of -22.2 ± 1.1‰ (n = 19). Benthic primary producers on Ronce-les-Bains tidal flats had δ13C values distinct from that of the POM: microphytobenthos (-16.0 ± 0.6‰), the macroalgae Enteromorpha compressa (-17.6 ± 2.8‰), Fucus serratus (-17.4 ± 2.6‰), Fucus vesiculosus (-18.5 ± 1.6‰), Phorphyra umbilicalis (-19.7 ± 0.5‰), Ulva rigida (-14.7 ± 2.0‰) and the seagrass Zostera noltii (-11.1 ± 1.0‰). Mean δ15N values of all macroalgae species ranged from 7.6 ± 1.3 to 8.9 ± 1.0‰, while those for microphytobenthos, POM and seagrass were 5.3 ± 0.8, 5.0 ± 0.9 and 6.5 ± 1.3‰, respectively. The mean δ13C value of spat (-15.3 ± 0.8‰) and juvenile cockles (-15.7 ± 0.7‰) varied within a smaller range than those of 1 to 4 yr old adults (-18.2 ± 1.2‰). The δ15N values of 0-group cockles (spat and juveniles) and adult cockles are similar (8.0 ± 0.9‰ for 0-group and 8.4 ± 1.1‰ for adults). The results suggest, based on the average trophic enrichment found in the literature for C and N, and the relative abundance of each food source, that there are 2 major sources of organic matter assimilated by cockles of the studied flats: microphytobenthos and POM. Seasonal variations in δ13C values reflect a higher dependence of adult cockles on POM variability while spat and juveniles are more closely linked to microphytobenthos. The isotopic shifts indicate that the relative importance of the 2 major food sources depends on the age of the cockles and the season

Kinetics of tidal resuspension of microbiota: Testing the effects of sediment cohesiveness and bioturbation using flume experiments

Resuspension of the top few sediment layers of tidal mud flats is known to enhance planktonic biomass of microbiota (benthic diatoms and bacteria). This process is mainly controlled by tidal shear stress and cohesiveness of mud, and is also influenced by bioturbation activities. Laboratory experiments in a race track flume were performed to test the interactive effects of these factors on both the critical entrainment and resuspension kinetics of microbiota from silt-clay sediments from the Marennes-Oleron Bay, France. The marine snail Hydrobia ulvae was used to mimic surface bioturbation activities. As expected, the kinetics of microbial resuspension versus shear stress were largely controlled by the cohesiveness of silt-clay sediments. However, our results indicate that the effect of surface tracking by H. ulvae on microbial resuspension was clearly dependent on the interaction between sediment cohesiveness and shear velocity. Evidence was also found that microphytobenthos and bacteria are not simultaneously resuspended from silt-clay bioturbated sediments. This supports the theory that diatoms within the easily eroded mucus matrix behave actively and bacteria adhering to fine silt particles eroded at higher critical shear velocities behave passively

Measurement of ingestion rate of <I>Hydrobia ulvae</I> (Pennant) on intertidal epipelic microalgae: the effect of mud snail density

International audienceThe individual mean ingestion rate of Hydrobia ulvae was measured experimentally in controlled microcosms, in the dark to avoid primary production during measurement and at constant temperature. The experimental design was based on the addition of prelabelled epipelic microalgae to microcosms in a constant proportion with unlabelled diatoms, and in such a way that algal food availability was not a limiting factor within the range of tested densities (0.3 to 4.1 snails cm−2). Results show that the individual mean ingestion rate decreased significantly from 26.6±1.1 ng Chl a snail−1 h−1 to 22.4±1.0 ng Chl a snail−1 h−1 between 0.7 and 3 snails cm−2. We hypothesize that this sharp decrease (the threshold density was between 1.4 and 2.5 snails cm−2) may account for a density-dependent effect. We have tested this hypothesis by using a simple random walk model including basic behavioural processes such as a break in feeding activity when two individuals contact each other. The model represents quantitatively well the threshold effect, suggesting that behavioural processes have to be taken into account for estimating a global feeding activity of H. ulvae populations

Carbohydrate production in relation to microphytobenthic biofilm development: an integrated approach in a tidal mesocosm

International audienceExperiments were performed to evaluate short-term changes in sediment extracellular carbohydratesfor a multispecific assemblage of benthic diatoms in relation to physiological status,endogenous migratory rhythms, and environmental conditions. For this purpose, a mesocosmwas used, which simulated both tidal and dark: light alternating cycles under controlled conditions.Scanning electronic microscopy in combination with picture analyses indicated thatnatural diatom migration patterns were reproduced in the mesocosm. Two EPS fractions wereoperationally separated in colloidal carbohydrate measurements: alcohol-soluble EPS (termed‘‘soluble EPS’’) and alcohol-insoluble EPS (termed ‘‘bound EPS’’). Microphytobenthic biomassfollowed a logistic-type curve and converged toward a maximal value termed the ‘‘biotic capacityof the local environment.’’ Both EPS fractions showed oscillations with production duringphotosynthetic periods and sharp decreases during night immersion periods. Productions ofboth EPS fractions increased with Chl a production during light periods suggesting a lightdependence in relation to migratory patterns. The decreases in both EPS fractions, which occurredduring night immersion periods suggest that carbohydrate hydrolysis and/or washawayaffected both EPS fractions similarly in benthic environments. Our results confirm the theoryaccording to which the two distinct fractions are under different metabolic controls. No changein soluble EPS release was obtained during the transition from logarithmic to stationary phase.On the other hand, a metabolism modification of microalgae, probably related to ammoniumdepletion, occurred when cells entered the stationary phase, since there was a high enhancementin bound EPS production. Mesocosm results can serve as a system of reference useful to characterizebiofilm development in field investigations and to revisit the effective implication ofeach EPS fraction in sediment stabilit

Spatio–temporal differentiation in the population structure of <I>Hydrobia ulvae</I> on an intertidal mudflat (Marennes-Oléron Bay, France)

International audienceSpatio–temporal changes in density, breeding cycle, growth and population structure of Hydrobia ulvae (Gastropoda: Prosobranchia) were studied by monthly sampling of a wide bare mudflat in Marennes-Oléron Bay. Four stations, located along a cross-shore transect and characterized by different geomorphological structures, were investigated from March 2000 to February 2001. Hydrobia ulvae was mainly distributed in the upper half part of the mudflat and no individuals were found in the lower part. The breeding cycle extended from March to December and showed two annual peaks, in spring and in autumn. Three cohorts were recruited during the year and showed high growth rates during summer; the parameters of the von Bertalanffy model describing the growth curves were equal to kmax=0·47±0·5 mm month−1 and L∞=5·4±0·2 mm. The snail population had similar size–frequency structure along the transect at the beginning of the survey but summer recruitment initiated spatial differentiation. Reproduction occurred in the middle part of the mudflat but recruits mainly settled down at the upper level of the mudflat; new cohorts appeared with increasing individual densities. The middle part of the mudflat was rather dominated by adult individuals which showed large density fluctuations

Invasion by the marine gastropod <I>Ocinebrellus inornatus</I> in France. III. Comparison of biological traits with the resident species <I>Ocenebra erinacea</I>

International audienceInvasive species impacts on native species and communities have been widely recognised for decades and may involve important economical losses. In this study, we examined two marine muricid gastropods: an invader, Ocinebrellus inornatus, and a resident, Ocenebra erinacea. Both species co-occur on French Atlantic coasts and probably have economical impacts on oyster farming areas of the Charente-Maritime region of France. In previous studies, we investigated the introduction source and the expansion patterns of O. inornatus, using molecular markers. However, these studies are not sufficient to fully understand the expansion dynamics of the exotics. The present framework is devoted to comparing life-history traits between the introduced and resident species. Our results first showed that O. inornatus has more favourable traits, such as a better mean growth rate and a higher reproductive effort, in comparison with O. erinacea. These traits may explain the invader establishment and, partly, its spread along the coast of France. Secondly, the resident species drilled a higher rate of oysters than the invader. Finally, the establishment of O. inornatus in France does not seem to be at the expense of O. erinacea because: (1) resources are not limiting in oyster farming areas and (2) there does not appear to be competition by interference between the species

Recent invasion of the Japanese oyster drill along the French Atlantic coast: identification of specific molecular markers that differentiate Japanese, <I>Ocinebrellus inornatus</I>, and European, <I>Ocenebra erinacea</I>, oyster drills

International audienceThe direct amplification of length polymorphism technique (DALP) has been used to distinguish species-specific banding patterns in two marine gastropod oyster drills Ocenebra erinacea (Linnaeus, 1758) and Ocinebrellus inornatus (Récluz, 1851). Ocenebra erinacea is the European oyster drill, common along all European coasts. Ocinebrellus inornatus, the Japanese oyster drill, was recorded in oyster growing areas of the Marennes-Oléron Bay (SW France) for the first time in 1995. This new biological invasion could lead to an increase, which must be evaluated, in the predation risk for cultivated species i.e. oysters and blue mussels, and for littoral fishing resources along the French Atlantic coasts. As a result, since specific identification of early life stages of both species (egg capsules and juveniles) was previously found to be both difficult and unsure using only morphological criteria, four Ocenebra erinacea and two Ocinebrellus inornatus specific molecular markers were identified and sequenced. These markers will facilitate the assessment of respective ecological impacts (reproductive patterns, abundance and spatial distribution of juveniles), resulting from the exotic species versus the native species and will allow us to analyse with certainty demographic profiles of the two oyster drill populations