Repeated Climate-driven dispersal and speciation in peripheral populations of Pleistocene mastodons

ecent ancient DNA work has shed some light on the responses of mastodons to Pleistocene glacial/interglacial cycling into Beringia. However, genetics has complicated our understanding of the relationships between Pacific and American mastodon phylogeography and questioned whether these are in fact two separate species or regionally localized morphotypes. Here we expand on both avenues by sequencing and contextualizing the mitochondrial genome of a Pacific mastodon, as well as from North American eastern coast specimens throughout the last 800 thousand years. We show that Pacific mastodons fall within a previously established, and deeply divergent mitochondrial clade, extending the range of this species into western Canada and potentially Mexico. We also present evidence for at least three discrete expansion events into north eastern coastal regions (i.e. Nova Scotia and the eastern continental shelf), and identify two new mastodon clades, which contain temporally distinct, but geographically co-occurrent mastodons. This work sheds further light on mastodon taxonomy and phylogeography across North America throughout the Pleistocene, highlighting interglacial range expansion into North-Eastern America mirroring the effects on the western side of the continent (Beringia).