EAGER: Effects of radiation on life history in “resurrected” Daphnia lineages exposed to fallout from 1950s atmospheric nuclear testing

1951年至1962年间，美国能源部在拉斯维加斯附近的内华达试验场(NTS)进行了地面试验，引爆了100枚核武器。由此产生的尘埃在亚利桑那州、内华达州和犹他州的大部分地区沉积了放射性物质。再加上世界各地数以百计的核试验，1945年广岛和长崎的原子弹爆炸，以及1986年和2011年切尔诺贝利和福岛第一核电站的事故，很明显，原子时代增加了全球人类和非人类生物体的放射性暴露。在短期内，辐射暴露会提高基因变化率(即突变)，并对所测试的大多数生物的生存和繁殖产生负面影响。然而，从长远来看，辐射暴露对进化的影响尚不清楚。随着时间的推移，突变率会保持在较高水平吗？人群是否适应承受辐射暴露？生存和繁殖是保持低迷还是恢复？这些问题的答案直接关系到福岛和切尔诺贝利等地附近人类和非人类人口的长期健康。它们更广泛地涉及到长期存在的问题，即突变率和自然选择在适应过程中如何相互作用。几名本科生和两名研究生将接受不同实验室和生物信息学分析方面的培训，包括代表人数不足的少数民族成员。这个项目的问题是：辐射暴露后野生种群是如何进化的？这是一个很难回答的问题，因为科学经常缺少辐射前的基线人口数据。此外，对于许多生物体来说，自辐射以来只有几代人过去了。这个项目使用一种世代时间短的有机体和一种称为复活生态学的方法来克服这两个问题。复活生态学是以休眠卵的形式收集的历史种群样本的集合，这些休眠卵是随着时间的推移而沉积在沉积物中的。特别是，这项研究侧重于大型水蚤属小型淡水甲壳类动物的休眠卵。水蚤每年都会产生卵子，在湖底过冬，然后在春天孵化。然而，这些蛋中的一些不会孵化，因为它们被沉积物掩埋了。这项研究将从NTS放射性沉降区内外的湖泊中采集沉积物岩心，以收集在地面核试验之前、期间和之后沉积的休眠水蚤卵。研究人员将孵化来自那个时代的卵子，并在实验室条件下饲养后代，以测量孵化率、存活率和繁殖率。如果辐射暴露对这些种群产生了负面影响，那么研究人员预计，在核试验期间和之后不久沉积的沉积物中的种群的存活率和繁殖率将相对较低。如果人们随着时间的推移适应辐射暴露，研究人员预测，最近的复活将有更高的存活率和繁殖率，与核之前的人口持平。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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. 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.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.