Microsatellite marker data for Chernobyl Daphnia populations

Populations experiencing varying levels of ionising radiation provide an
excellent opportunity to study the fundamental drivers of evolution.
Radiation can cause mutations, and
thus supply genetic variation; it can also
selectively remove individuals that are unable to cope
with the physiological stresses associated
with radiation exposure, or non-selectively
cull swathes of the population, reducing genetic variation. Since the
nuclear power plant explosion in 1986, the Chernobyl area has experienced
a spatially heterogeneous exposure to varying levels of ionising
radiation. We sampled Daphnia pulex (a freshwater crustacean) from lakes across the Chernobyl area, genotyped them at ten microsatellite loci, and also calculated the current radiation dose rates. We then investigated whether the pattern of genetic diversity was positively associated with radiation dose rates, consistent with radiation-mediated supply of de novo mutations, or negatively associated with radiation dose rates, as would be expected with strong radiation-mediated selection. We found that measures of genetic diversity, including expected heterozygosity and mean allelic richness (an unbiased indicator of diversity) were significantly higher in lakes that experienced the highest radiation dose rates. This suggests that mutation outweighs selection as the key evolutionary force in populations exposed to high radiation dose rates. We also found significant but weak population structure, indicative of low genetic drift, and clear evidence for isolation by distance between populations. This further suggests gene flow between nearby populations is eroding population structure, and that mutational input in high radiation lakes could, ultimately, supply genetic variation to lower radiation sites.