Evolution of mutation rate in astronomically large phytoplankton populations
<p>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,...
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| Format: | Journal article |
| Language: | English |
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Oxford University Press
2020
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| Summary: | <p>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 <em>Emiliania huxleyi</em> (Haptophyta) that has modest genetic diversity despite an astronomically large population size. Genome sequencing of <em>E. huxleyi</em> mutation accumulation lines revealed 455 mutations, with an unusual GC-biased mutation spectrum. This yielded an estimate of the per site mutation rate <em>µ</em>=5.55x10<sup>−10</sup> (CI 95%: 5.05x10<sup>−10</sup> – 6.09x10<sup>−10</sup>), which corresponds to an effective population size <em>N<sub>e</sub></em>∼2.7x10<sup>6</sup>. Such a modest <em>N<sub>e</sub></em> 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<sup>−10</sup> 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.</p> |
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