NSF Award
2028775
Between 1951 and 1962, the U.S. Department of Energy detonated one hundred nuclear weapons during above-ground testing at the Nevada Test Site (NTS), near Las Vegas. The resulting fallout deposited radioactivity across much of Arizona, Nevada, and Utah. Together with hundreds more tests around the world, the bombings of Hiroshima and Nagasaki in 1945, as well as the 1986 and 2011 accidents at Chernobyl and Fukushima Daiichi power plants, it is clear that the atomic age has increased radioactive exposure for human and non-human organisms around the globe. In the short term, radiation exposure raises rates of genetic change (i.e., mutation) and negatively affects survival and reproduction for most organisms tested. In the long term, however, the evolutionary impacts of radiation exposure are not yet clear. Do mutation rates stay elevated over time? Do populations adapt to withstand radiation exposure? Do survival and reproduction stay depressed or recover? Answers to these questions are directly relevant to the long term health of human and non-human populations near places like Fukushima and Chernobyl. They are more broadly relevant to long-standing questions about how mutation rate and natural selection interact during adaptation. Several undergraduates and two graduate students will be trained in diverse laboratory and bioinformatic analyses, including members of underrepresented minorities. <br/><br/>This project asks: how have wild populations evolved following radiation exposure? This is a difficult question to answer because science is often missing baseline, pre-radiation population data. Moreover, for many organisms, only a few generations have passed since irradiation. This project overcomes both of these problems using an organism with short generation times and an approach called resurrection ecology. Resurrection ecology is the collection of historical population samples in the form of dormant eggs that have been deposited through time in sediments. In particular, this research focuses on dormant eggs of small, freshwater crustaceans in the genus Daphnia. Daphnia create annual egg deposits that spend the winter on lake bottoms before hatching in the spring. Some of these eggs do not hatch, however, because they are buried by sediment. This study will take sediment cores from lakes inside and out of the NTS radioactive fallout zone to collect dormant Daphnia eggs deposited before, during, and after above ground nuclear testing. The researchers will hatch eggs from those eras and raise offspring in laboratory conditions to measure rates of hatching, survival, and reproduction. If radiation exposure negatively impacted these populations, then researchers expect that populations from sediments deposited during and shortly after nuclear testing will have relatively low rates of survival and reproduction. If populations adapt to radiation exposure over time, the researchers predict that more recent resurrections will have higher rates of survival and reproduction, on par with pre-nuclear populations.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
