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International audience; This study examined chronic effects of external Cs-137 gamma radiation on Daphnia magna exposed over three successive generations (F0, F1 and F2) to environmentally relevant dose rates (ranging from 0.007 to 35.4mGyh-1). Investigated endpoints included survival, growth, reproduction and DNA alterations quantified using random-amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). Results demonstrated that radiation effects on survival, growth and reproduction increased in severity from generation F0 to generation F2. Mortality after 21 days at 35.4mGyh-1 increased from 20% in F0 to 30% in F2. Growth was affected by a slight reduction in maximum length at 35.4mGyh-1 in F0 and by reductions of 5 and 13% in growth rate, respectively, at 4.70 and 35.4mGyh-1 in F2. Reproduction was affected by a reduction of 19% in 21 day-fecundity at 35.4mGyh-1 in F0 and by a delay of 1.9 days in brood release as low as 0.070mGyh-1 in F2. In parallel, DNA alterations became significant at decreasing dose rates over the course of F0 (from 4.70mGyh-1 at hatching to 0.007mGyh-1 after ~21 days) and from F0 to F2 (0.070mGyh-1 at hatching to 0.007mGyh-1 after ~21 days), demonstrating their rapid accumulation in F0 daphnids and their transmission to offspring generations. Transiently more efficient DNA repair leading to some recovery at the organism level was suggested in F1, with no effect on survival, a slight reduction of 12% in 21 day-fecundity at 35.4mGyh-1 and DNA alterations significant at highest dose rates only. The study improved our understanding of long term responses to low doses of radiation at the molecular and organismic levels in a non-human species for a better radioprotection of aquatic ecosystems. © 2015 Elsevier B.V.

This study aimed to examine the mechanisms involved in the transgenerational increase in Daphnia magna sensitivity to waterborne depleted uranium (DU) under controlled laboratory conditions. Daphnids were exposed to concentrations ranging from 2 to 50 μg L-1 over two successive generations. Genotoxic effects were assessed using random amplified polymorphic DNA and real time PCR (RAPD-PCR). Effects on life history (survival, fecundity and somatic growth) were monitored from hatching to release of brood 5. Different exposure regimes were tested to investigate the specific sensitivity of various life stages to DU. When daphnids were exposed continuously or from hatching to deposition of brood 5, results demonstrated that DNA damage accumulated in females and were transmitted to offspring in parallel with an increase in severity of effects on life history across generations. When daphnids were exposed during the embryo stage only, DU exposure induced transient DNA damage which was repaired after neonates were returned to a clean medium. Effects on life history remained visible after hatching and did not significantly increase in severity across generations. The present results suggest that DNA damage might be an early indicator of future effects on life history. © 2013 Elsevier Inc.

The effects of radiation on biological systems have been studied for many years, and it is now accepted that direct damage to DNA from radiation is the triggering event leading to biological effects. In the present study, DNA damage induced by acute or chronic irradiation was compared at the cellular (zebrafish [Danio rerio] cell line ZF4) and developmental (embryo) levels. Zebrafish ZF4 cells and embryos (at 3h postfertilization) were exposed within ranges of acute doses (0.3-2Gy/d) or chronic dose rates (0.1-0.75Gy/d). DNA damage was assessed by immunodetection of \textgreekg-H2AX and DNA-PK (DNA double-strand breaks) and the alkaline comet assay (DNA single-strand breaks). Zebrafish embryo development and DNA damage were examined after 120h. At low doses, chronic irradiation induced more residual DNA damage than acute irradiation, but embryo development was normal. From 0.3Gy, a hyper-radiosensitivity phenomenon compared to other species was shown for acute exposure with an increase of DNA damage, an impairment of hatching success, and larvae abnormalities. These results suggest a dose-dependent correlation between unrepaired DNA damage and abnormalities in embryo development, supporting the use of DNA repair proteins as predictive biomarkers of ionizing radiation exposure. This could have important implications for environmental protection. © 2011 SETAC.