Themes: Agronomy, Ecology
location: Laboratory for Radionuclide Ecotoxicology (LECO) - Cadarache (13)
Master degree in evolutionary biology, ecology, ecotoxicology, ecophysiology / maintenance and experimentation of living organisms / biological, biochemical analysis tools / modeling, statistical analyses.
Age limit: 26 years old unless otherwise stated.
The question of estimating the dose rate above which ionizing radiation becomes harmful to ecosystems on the long-term remains controversial and represents a priority research action in radiation protection at IRSN. The proposed PhD project will be co-supervised by Dr. Frédéric ALONZO (IRSN, Cadarache, France) and Dr. Stuart AULD (University of Stirling, UK). This project will aim to study, under laboratory conditions, long term responses to gamma ionizing radiation (Cs-137) in an aquatic invertebrate, which has been collected in the Chernobyl Exclusion Zone (CEZ). The objective here will be to examine whether exposed populations can gain an increased capacity to face radiological stress, due to the selection of resistant genotypes. The problem will be addressed in a planktonic cladoceran invertebrate, Daphnia pulex, which can be found in freshwater ponds across Chernobyl Exclusion Zone. The proposed approach includes 3 axes: - an experimental part, exposing clones of daphnids collected in Chernobyl to external gamma radiation (Cs-137) over several generations. Life history traits (survival, growth and reproduction curves) will be monitored on a range of dose rates (from background to significantly toxic), together with a collection of samples in order to analyze possible underlying mechanisms of action: genetic damage (strand breaks, mutations), modifications of epigenetic and/or transcriptomic profiles, cellular damage (oxidative stress, apoptosis) etc. - a mathematical modelling part, based on toxicokinetic-toxicodynamic approaches, including GUTS (General Unified Threshold model of Survival) and DEBtox (Dynamic Energy Budget applied to Toxicology) which are used to analyze survival, growth and reproduction curves as a function of dose rate, to identify metabolic modes of action likely involved and to explain how effects can vary in severity over time, in particular from one generation to the next due to cumulated genetic damage. - finally an evolutionary biology part, that will aim to analyze changes in life history and dynamic energy budget among daphnid clones, exposed in Chernobyl to dose rates ranging (nowadays) from 0.1 µGy/h to 200 µGy/h. To do so, life history and metabolic traits will be compared among clones in order to determine whether biological and/or toxicokinetic-toxicodynamic processes have eventually adapt, as a result of natural selection in the CEZ.