Bison phylogeography constrains dispersal and viability of the Ice Free Corridor in western Canada

Abstract

The Ice Free Corridor has been invoked as a route for Pleistocene human and animal dispersals between eastern Beringia and more southerly areas of North America. Despite the significance of the corridor, there are limited data for when and how this corridor was used. Hypothetical uses of the corridor include: the first expansion of humans from Beringia into the Americas, northward postglacial expansions of fluted point technologies into Beringia, and continued use of the corridor as a contact route between the north and south. Here, we use radiocarbon dates and ancient mitochondrial DNA from late Pleistocene bison fossils to determine the chronology for when the corridor was open and viable for biotic dispersals. The corridor was closed after ∼23,000 until 13,400 calendar years ago (cal y BP), after which we find the first evidence, to our knowledge, that bison used this route to disperse from the south, and by 13,000 y from the north. Our chronology supports a habitable and traversable corridor by at least 13,000 cal y BP, just before the first appearance of Clovis technology in interior North America, and indicates that the corridor would not have been available for significantly earlier southward human dispersal. Following the opening of the corridor, multiple dispersals of human groups between Beringia and interior North America may have continued throughout the latest Pleistocene and early Holocene. Our results highlight the utility of phylogeographic analyses to test hypotheses about paleoecological history and the viability of dispersal routes over time.

Keywords: Clovis; Pleistocene; bison; ice free corridor; phylogeography.

Fig. 1.

The geographic distribution and clade assignment of 192 radiocarbon dated or present-day North American bison. Bison distribution (A) >23,000 cal y BP, before the period of glacial coalescence; (B) 23,000–13,500 cal y BP, during the period of glacial coalescence; (C) 13,500–12,000 cal y BP, as the corridor opens; and (D) <12,000 cal y BP. Bison mitochondrial sequences fall into two main genetic clades (11): clade 1a arises in the south during the interval depicted in B. Ice margins are from ref. : (A) pre-LGM margin at 23,000 cal y BP estimated following discussion of probable marine isotope stage 3 margin in ref. ; (B) 17,900 cal y BP; (C) 13,000 cal y BP; (D) 10,700 cal y BP. Sea levels are from ref. : (A) −55 m; (B) −100 m; (C) −65 m; and (D) −40 m. Specific localities: Anzick (AZ), Calgary (CA), Charlie Lake Cave (CLC), Dry Creek (DC), Edmonton/Clover Bar (E/CB), Gault (G), Liard River (LI), Paisley Caves (PC), Upward Sun River (USR), Vermilion Lakes (VL), and Wally's Beach (WB). Map modified from ESRI ArcGIS Online; source: US National Park Service and US Geological Survey, east view cartographic.

Fig. S1.

A tip-labeled, time-calibrated mitochondrial genealogy of 192 bison obtained from a Bayesian analysis of ∼600 bp of the mitochondrial control region, as in Fig. 1. Node values are Bayesian posterior probabilities and tip labels correspond to samples in Dataset S1. Bars are 95% highest posterior probability density intervals for node heights and are shown for nodes with posterior probability values of >95%.

Fig. 2.

(A) A time-calibrated maximum clade credibility mitochondrial genealogy resulting from a Bayesian phylogeographic analysis of ∼600 bp of the mitochondrial control region amplified from 192 bison. Clades 1 and 2 are denoted by orange and purple, as in Fig. 1, with the three late-surviving clades (1a, 2a, and 2b) highlighted. Gray and red branches represent haplotypes sampled from localities north and south of 60° N, respectively. This latitude is assumed to be the location of a final barrier to a traversable corridor (56). Yellow stars denote nodes supported by posterior probabilities >90%, as inferred from the Bayesian analysis. (B) Density plots representing the timing of movements between north and south of 60° N. The plots have been rescaled so that the highest peaks are of equal height. The period of glacial coalescence (PGC) is overlain in gray between 23,000–13,500 cal y BP.