Year 1: Daphnia distribution and radiation dose over space and time. Three sediment cores will be obtained from each of eight lakes from across the CEZ. The cores will be measured and split longitudinally; Daphnia resting eggs will be isolated from along one half of each sediment core. With the other half of each core, we will conduct cutting-edge analysis using the distributions of Plutonium 139 (high energy alpha radiation) Caesium 137, Lead 210, Americium 241 and Strontium 90 (lower energy gamma radiation) isotopes to determine how radioactive material was deposited in freshwater lakes, and then determine the radiation dose rate experienced by organisms that inhabit those lakes (including Daphnia). The student will then conduct a large-scale hatching programme, following proven methods, to revive the Daphnia eggs from dormancy; these hatched Daphnia will be propagated by asexual reproduction to establish independent genetic lines from different Chernobyl lakes at different historical time points. The project will aim to address the following points, although its exact trajectory will depend on the studentÃ¢â‚¬â„¢s own interests and initial results:
Q1.1: How patchy was the deposition of radioactive material within lakes before the nuclear reactor was built, during normal operation, and immediately after the accident?
Q1.3: How does the spatio-temporal distribution of Daphnia resting eggs covary with radiation dose rate within and across Chernobyl lakes?
Year 2: Radiation and Daphnia trait evolution. Using the genotype lines established in Year 1, the student will conduct a suite of standard Daphnia life history experiments to quantify how key fitness traits such as asexual replication rate, propensity to produce male offspring, lifespan and reproductive senescence vary with respect to radiation dose and lake. The experiments will be blocked according to lake, and there will be a minimum of 100 genotypes per lake (x 3 replicates per genotype). This experiment will allow the student to answer the following questions:
Q2.1: Does radiation dose rate fuel phenotypic evolution in Daphnia?
Q2.2: Can rapid adaptive evolution in Daphnia populations mitigate the negative impacts of exposure to radiation?
Year 3: Population genetic consequences of the Chernobyl accident in Daphnia. Using simple and well-established microsatellite genetic tools, the student will be able to examine how genetic diversity and population structure has changed over space and time. S/he will use microsatellites to: (1) quantify the supply of alleles, i.e., the supply of genetic variation, over time; (2) look for evidence that some pre-accident alleles either disappear or become rare, and evaluate whether this is due to a massive population bottleneck, or due to radiation-mediated selection; and (3) test whether there is significant arrival of genetic variants from neighbouring lakes, as would occur if migration of radiation-resistant Daphnia allowed for the recolonization of lakes after the Chernobyl accident. This will allow them to ask:
Q3.1: Is there an association between radiation dose rate and the supply of microsatellite alleles, i.e., the supply of genetic variation, over time
Q3.2: Is there evidence of an extreme population bottleneck or gene flow associated with post-accident recolonization of lakes?
Year 3.5: Synthesis of phenotypic and population genetic data. In the final six months, the student will have the opportunity to quantify the extent to which phenotypic change and population genetic patterns are linked. S/he can then evaluate these relationships and look for evidence of radiation-mediated selection on the Chernobyl Daphnia populations over time. We envisage that this project has the potential to generate 5-6 first-author papers for the student, produced throughout the PhD with the first potentially being written by the end of the 1st year.