Fossil and genomic evidence constrains the timing of bison arrival in North America

Abstract

The arrival of bison in North America marks one of the most successful large-mammal dispersals from Asia within the last million years, yet the timing and nature of this event remain poorly determined. Here, we used a combined paleontological and paleogenomic approach to provide a robust timeline for the entry and subsequent evolution of bison within North America. We characterized two fossil-rich localities in Canada’s Yukon and identified the oldest well-constrained bison fossil in North America, a 130,000-y-old steppe bison, Bison cf. priscus. We extracted and sequenced mitochondrial genomes from both this bison and from the remains of a recently discovered, ∼120,000-y-old giant long-horned bison, Bison latifrons, from Snowmass, Colorado. We analyzed these and 44 other bison mitogenomes with ages that span the Late Pleistocene, and identified two waves of bison dispersal into North America from Asia, the earliest of which occurred ∼195–135 thousand y ago and preceded the morphological diversification of North American bison, and the second of which occurred during the Late Pleistocene, ∼45–21 thousand y ago. This chronological arc establishes that bison first entered North America during the sea level lowstand accompanying marine isotope stage 6, rejecting earlier records of bison in North America. After their invasion, bison rapidly colonized North America during the last interglaciation, spreading from Alaska through continental North America; they have been continuously resident since then.

A middle Holocene steppe bison and paleoenvironments from the Versleuce Meadows, Whitehorse, Yukon, Canada

“…Separate analyses of bison mitochondrial genomes confirm that both subspecies of extant bison (B. bison) form a single, wellsupported cluster (Clade 1A) within the greater diversity of North American bison (Shapiro et al 2004;Heintzman et al 2016;Froese et al 2017;Fig. 6).…”

“…We constructed a consensus sequence following Heintzman et al (2016), except that we retained the entire mitochondrial genome (GenBank accession number MF134653). We compared the Versleuce Meadows bison mitogenome sequence to a previously published alignment (Froese et al 2017), which consists of mitochondrial genome sequences from 46 North American or Siberian bison and four yak. We performed a phylogenetic timetree analysis using BEAST (v1.8.1; Drummond et al 2012) utilizing parameters outlined in Froese et al (2017).…”

“…We compared the Versleuce Meadows bison mitogenome sequence to a previously published alignment (Froese et al 2017), which consists of mitochondrial genome sequences from 46 North American or Siberian bison and four yak. We performed a phylogenetic timetree analysis using BEAST (v1.8.1; Drummond et al 2012) utilizing parameters outlined in Froese et al (2017). Briefly, we partitioned the data, used a strict molecular clock informed by radiocarbon or stratigraphic data (with independent rates for each partition), and a skygrid coalescent prior (Gill et al 2013).…”

“…Fossil records suggest that once bison initially dispersed from Asia across the exposed Bering Isthmus 195-135 thousand years ago (Froese et al 2017), they subsequently established themselves as the most abundant, large Pleistocene ungulate in many parts of North America (Guthrie 1970(Guthrie , 1990McDonald 1981). Estimates suggest that typical late Pleistocene mammal faunas in eastern Beringia are composed of over 80% steppe bison (B. priscus) remains (Guthrie 1990).…”

“…Genetic studies based on mitochondrial DNA from Quaternary bison have shown that extant bison, B. bison, arose during the last glacial maximum from ancestors situated south of the continental ice sheets, and that B. bison mitochondrial variation falls within a much more diverse bison complex (including the steppe bison, B. priscus) that occurred both north and south of the ice sheets during the late Pleistocene (Shapiro et al 2004;Heintzman et al 2016;Froese et al 2017). As mitochondrial DNA sequences can distinguish B. bison from other bison taxa, they can be used to infer the systematic status and phylogeographic history of enigmatic bison specimens.…”