Resolving taxonomic uncertainty in vulnerable elasmobranchs : are the Madeira skate (Raja maderensis) and the thornback ray (Raja clavata) distinct species?

Skates and rays constitute the most speciose group of chondrichthyan fishes, yet are characterised by remarkable levels of morphological and ecological conservatism. They can be challenging to identify, which makes monitoring species compositions for fisheries management purposes problematic. Owing to their slow growth and low fecundity, skates are vulnerable to exploitation and species exhibiting endemism or limited ranges are considered to be the most at risk. The Madeira skate Raja maderensis is endemic and classified as ‘Data Deficient’ by the IUCN, yet its taxonomic distinctiveness from the morphologically similar and more wide-ranging thornback ray Raja clavate is unresolved. This study evaluated the sequence divergence of both the variable control region and cytochrome oxidase I ‘DNA barcode’ gene of the mitochondrial genome to elucidate the genetic differentiation of specimens identified as R. maderensis and R. clavate collected across much of their geographic ranges. Genetic evidence was insufficient to support the different species designations. However regardless of putative species identification, individuals occupying waters around the Azores and North African Seamounts represent an evolutionarily significant unit worthy of special consideration for conservation management

Détection à très grand angle solide: Application à la NRA

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Membrane-Dependent Bystander Effect Contributes to Amplification of the Response to Alpha-Particle Irradiation in Targeted and Nontargeted Cells

International audienceFree radicals are believed to play an active role in the bystander response. This study investigated their origin as well as their temporal and spatial impacts in the bystander effect.We employed a precise alpha-particle microbeam to target a small fraction of subconfluent osteoblastic cells (MC3T3-E1). γH2AX-53BP1 foci, oxidative metabolism changes, and micronuclei induction in targeted and bystander cells were assessed.Cellular membranes and mitochondria were identified as two distinct reactive oxygen species producers. The global oxidative stress observed after irradiation was significantly attenuated after cells were treated with filipin, evidence for the primal role of membrane in the bystander effect. To determine the membrane's impact at a cellular level, micronuclei yield was measured when various fractions of the cell population were individually targeted while the dose per cell remained constant. Induction of micronuclei increased in bystander cells as well as in targeted cells and was attenuated by filipin treatment, demonstrating a role for bystander signals between irradiated cells in an autocrine/paracrine manner.A complex interaction of direct irradiation and bystander signals leads to a membrane-dependent amplification of cell responses that could influence therapeutic outcomes in tissues exposed to low doses or to environmental exposure

Mesures de stabilité de la Microsonde de Saclay

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Projet SIRMIO : Visualisation temps réel des traces d’ionisations alpha/proton

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Population structure of the thornback ray (Raja clavata L.) in British waters

Prior to the 1950s, thornback ray (Raja clavata L.) was common and widely distributed in the seas of Northwest Europe. Since then, it has decreased in abundance and geographic range due to over-fishing. The sustainability of ray populations is of concern to fisheries management because their slow growth rate, late maturity and low fecundity make them susceptible to exploitation as victims of by-catch. We investigated the population genetic structure of thornback rays from 14 locations in the southern North Sea, English Channel and Irish Sea. Adults comprised <4% of the total sampling despite heavy sampling effort over 47 hauls; thus our results apply mainly to sexually immature individuals. Using five microsatellite loci, weak but significant population differentiation was detected with a global FST = 0.013 (P <0.001). Pairwise Fst was significant for 75 out of 171 comparisons. Although earlier tagging studies suggest restricted foraging distances from home areas, the absence of genetic differentiation between some distant populations suggests that a substantial fraction of individuals migrate over wide areas. Autumn/winter locations appear to have a lower level of differentiation than spring/summer, which could be due to seasonal migration. Management and conservation of thornback ray populations will be challenging as population structure appears to be dynamic in space and tim