Somatic mutation rates in Acropora hyacinthus

Exogenous mutagens can increase the mutation rate and genomic instability. One such mutagen is ionizing radiation, a byproduct of nuclear fission technologies. For all the discussion about nuclear technology over the last seven decades, little has been done to assess the effects of radiation on wild populations. The lack of publicly available knowledge is particularly stark in the Marshall Islands, where the U.S. Navy tested nuclear weapons from 1946-1958. We measured somatic mutation rates and patterns in coral colonies living at Enewetak and Bikini Atolls, two former nuclear testing sites, as well as two non-irradiated sites, Palau and American Samoa. On average, the somatic mutation rate was not higher for corals living in Enewetak and Bikini than those living in American Samoa and Palau. Two colonies, one from Bikini and one from Enewetak, showed 4-10 times high somatic mutation rates, but not higher single nucleotide variant rates. Structural variants like indels and balanced inversions tend to be signatures of ionizing radiation. There was no relationship between the number of genetic differences in two samples from a coral and the physical distance between those two samples, indicating that colony size is not a reliable proxy for the accumulation of somatic mutations. The Enewetak coral population was less genetically diverse than the other three, perhaps due to a bottleneck or founder effect as a result of widespread coral mortality in the 1940s-50s. A broader survey of more corals is needed to determine the frequency of individuals with very high somatic mutation rates.