Genetic diversity is expected to be proportional to population size, yet, there is a well-known, but unexplained lack of genetic diversity in large populations – the “Lewontin’s paradox”. Larger populations are expected to evolve lower mutation rates, which may help to explain this paradox. Here we test this conjecture by measuring the spontaneous mutation rate in a ubiquitous unicellular marine phytoplankton species Emiliania huxleyi (Haptophyta) that has modest genetic diversity despite an astronomically large population size. Genome sequencing of E. huxleyi mutation accumulation lines revealed 455 mutations, with an unusual GC-biased mutation spectrum. This yielded an estimate of the per site mutation rate µ=5.55x10⁻¹⁰ (CI 95%: 5.05x10⁻¹⁰ – 6.09x10⁻¹⁰), which corresponds to an effective population size N_e∼2.7x10⁶. Such a modest N_e is surprising for a ubiquitous and abundant species that accounts for up to 10% of global primary productivity in the oceans. Our results indicate that even exceptionally large populations do not evolve mutation rates lower than ∼10⁻¹⁰ per nucleotide per cell division. They rule out the possibility that the extreme disparity between modest genetic diversity and astronomically large population size in the plankton species is due to an unusually low mutation rate.

中文翻译：

---

天文大型浮游植物种群突变率的演变。

遗传多样性预计将与人口规模成正比，但是，众所周知，大人口中遗传多样性缺乏，这是无法解释的，这就是“李文汀悖论”。预期较大的人群将产生较低的突变率，这可能有助于解释这一悖论。在这里，我们通过测量普遍存在的单细胞海洋浮游植物物种Emiliania huxleyi（Haptophyta）的自发突变率来测试该猜想，该物种尽管天文数字庞大，但遗传多样性不高。赫氏大肠杆菌（E. huxleyi）突变累积株的基因组测序显示455个突变，具有不寻常的GC偏向突变谱。得出每个位点突变率的估计值μ = 5.55x10 ^-10（CI 95％：5.05x10 ^-10 - 6.09x10 ^-10），其对应于一个有效群体大小Ñ _Ë ~2.7x10 ⁶。如此适度的N _e令人惊讶，因为它们无处不在且种类繁多，占海洋总初级生产力的比例高达10％。我们的结果表明，即使是非常大的种群，其每细胞分裂所产生的突变率也不会低于每核苷酸〜10 ^-10。他们排除了浮游生物物种中适度的遗传多样性与天文数字上的巨大种群之间的极端差异是由于异常低的突变率造成的可能性。