Figure 5. Orang-utan population genetics and demographics.
a, Site-frequency spectra for 13.2 × 106 Bornean (red) and Sumatran (blue) SNPs are shown based on the ascertainment of 10 chromosomes per species; note the enrichment of low-frequency SNPs among Sumatran individuals. b, The majority of SNPs were restricted to their respective island populations as the ‘heat’ of the two-dimensional site-frequency spectra, representing high allele counts, lay along the axes. c, Our demographic model estimated that the ancestral orang-utan population (Ne = 17,900) split approximately 400,000 years ago, followed by exponential expansion of Sumatran Ne and a decline of Bornean Ne, culminating in higher diversity among modern Sumatran orang-utans despite a lower census population size. The model also supported low-level gene flow (<1 individual per generation), indicated by arrows.