Abstract

The rates and patterns of somatic mutations in wild plants, as well as how they relate to longevity, are largely unknown. Here, we examined the somatic mutation landscapes of slow- and fast-growing tropical species in central Borneo, Indonesia. Using newly-constructed genomes, we identified an average of 480 mutations in the slow-growing species (265-year-old, 44.1 m in height), which was five times greater than that observed in the fast-growing species (66-year-old, 43.9 m). The number of somatic mutations increased linearly with branch length. The somatic mutation rate per meter was higher in the slow-growing species, yet the rate per year remained constant across both species. The mutational spectra exhibited a dominance of spontaneous mutations, specifically cytosine-to-thymine substitutions at CpG sites. An analysis of nucleotide substitutions at both the intra- and inter-individual level revealed that somatic mutations are neutral within an individual, but those mutations transmitted to the next generation are subject to purifying selection. We developed a model to evaluate the relative contribution of cell division on mutational processes, and postulate that cell-division independent mutagenesis predominates. These findings deepen our understanding of mutational processes underlying the generation of genetic diversity in a tropical ecosystem.