UBC Theses and Dissertations

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UBC Theses and Dissertations

Heritable somatic mutations accumulate slowly in Sitka spruce but increase the per-generation mutation rate considerably Hanlon, Vincent Charles Terrence


The rate and biological significance of heritable somatic mutations accumulating with vegetative growth or age in trees has long been a subject of debate. Somatic mutation rates are unknown for conifers, some of which can reach exceptional sizes and ages. I investigated the somatic mutation rate in the conifer Sitka spruce (Picea sitchensis (Bong.) Carr.) by sequencing 113.1 Mb of nuclear DNA from the top and bottom of 20 exceptional old growth trees averaging 76 m in height. I estimate a somatic base substitution rate of 2.7 x 10-⁸ per base pair within a generation. Since this is comparable to germline mutation rates in the fastest-mutating eukaryotes, somatic mutations increase the per-generation heritable mutation rate in conifers considerably; but because these Sitka spruce are old, the increase is very small on an annual basis. I argue that although somatic mutations raise genetic loads in conifers, they generate important genetic variation, and they may also enable selection among cell lineages within individual trees.

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