Genomic DNA Sequences from Mastodon and Woolly Mammoth Reveal Deep Speciation of Forest and Savanna Elephants
Demographic model that is fit by MCMCcoal, in which all population splits are instantaneous (without subsequent gene flow), and all population sizes are assumed to be constant over intervals. Here, TFS refers to forest-savanna elephant population divergence time, TAM refers to Asian elephant-mammoth population divergence time, TLox-Eur refers to African-Eurasian population divergence time, and TElephantid-Mastodon refers to elephantid-mastodon population divergence time, presented here in millions of years. The Ν quantities refer to constant diploid effective population sizes ancestral to each of these splits (in thousands). For obtaining estimates of years and population sizes, we assume that the elephantids have an average of 31 years per generation, based on estimates of 17–20 years for females , and 40–49 years for males ,. A lower or higher number of years per generation would produce a proportionate effect on the population size estimates. For each parameter, two sets of numbers are shown. The upper set shows the range consistent with the fossil record, calibrating to an assumed African-Eurasian population split of TLox-Eur = 4.2–9 Mya (justified in Text S5). For example for forest-savanna population divergence, this leads to TFS = 2.6–5.6 Mya given that MCMCcoal estimates TFS/TLox-Eur = 62%. The lower set of numbers (in parentheses) provides MCMCcoal's 90% credible interval for the parameters as a fraction of the best estimate (e.g. 76%–126% for TFS). In the main text, we conservatively quote a range that combines the uncertainty from the fossil record and from MCMCcoal (e.g. TFS = 1.9–7.1 Mya).