Testing the Effect of the Toba Volcanic Eruption on Population Sizes in Worldwide Mammal Species

The volcanic eruption of Toba in northern Sumatra at 71 kyBP ({+/-}5 kyBP) emitted sulfur gas and deposited thick layers of dust throughout the surrounding region. It is thought to have had a significant and dramatic cooling impact on the paleoclimate worldwide. Ambrose [1] conjectured this to be the cause of the contemporaneous (50-100 kyBP) population bottleneck observed in humans. We hypothesize that a volcanic winter of sufficient magnitude to cause a population bottleneck in humans would similarly affect other mammals. To test this hypothesis, we estimated pairwise mismatch distributions using mtDNA control region sequences of 28 mammal species archived on NCBI to assess whether each species underwent a population bottleneck. For any species fitting the sudden expansion model, we estimated the timing of the bottleneck and compared it to the date range of the Toba eruption. Only 3 of the 28 species show evidence of rapid population expansion overlapping in time with the Toba eruption. Therefore, the hypothesis that the volcanic winter triggered by the Toba eruption caused a significant bottleneck impacting mammal species worldwide is not supported by mitochondrial evidence. Our results question the hypothesis that the Toba eruption contributed to the bottleneck observed in humans at this time.