Lions and brown bears colonized North America in multiple synchronous waves of dispersal across the Bering Land Bridge

Abstract

The Bering Land Bridge connecting North America and Eurasia was periodically exposed and inundated by oscillating sea levels during the Pleistocene glacial cycles. This land connection allowed the intermittent dispersal of animals, including humans, between Western Beringia (far north-east Asia) and Eastern Beringia (north-west North America), changing the faunal community composition of both continents. The Pleistocene glacial cycles also had profound impacts on temperature, precipitation, and vegetation, impacting faunal community structure and demography. While these paleoenvironmental impacts have been studied in many large herbivores from Beringia (e.g., bison, mammoths, horses), the Pleistocene population dynamics of the diverse guild of carnivorans present in the region are less well understood, due to their lower abundances. In this study, we analyze mitochondrial genome data from ancient brown bears (Ursus arctos; n = 103) and lions (Panthera spp.; n = 39), two megafaunal carnivorans that dispersed into North America during the Pleistocene. Our results reveal striking synchronicity in the population dynamics of Beringian lions and brown bears, with multiple waves of dispersal across the Bering Land Bridge coinciding with glacial periods of low sea levels, as well as synchronous local extinctions in Eastern Beringia during Marine Isotope Stage 3. The evolutionary histories of these two taxa underscore the crucial biogeographic role of the Bering Land Bridge in the distribution, turnover, and maintenance of megafaunal populations in North America.

Ancient horse genomes reveal the timing and extent of dispersals across the Bering Land Bridge

“…Finally, our study demonstrates the advantage of genomics in identifying the role of the BLB not only as a biogeographical corridor, but also as a critical contact zone where significant evolutionary processes unfolded for Holarctic cold adapted taxa (Figure 4). Our data show that horses dispersed back into North America from Eurasia around the same time as the initial expansion of bison, brown bears and lions through the BLB (Froese et al, 2017; Salis et al, 2020). When present, the BLB clearly played a key role as a bicontinental dispersal corridor for many taxa, including ones that used it more than once (Debruyne et al, 2008; Elias & Crocker, 2008; Froese et al, 2017; Meiri et al, 2014, 2020).…”

“…Reconstructions of first appearance dates (FADs) for different mammals dispersing across the BLB support the conclusion that optimal conditions for dispersal were intermittent and varied by taxon (Salis et al, 2020). The current North American FAD for mammoths, for example, is the Early Pleistocene, ~1.5 Ma (Lister & Sher, 2015), while bison first entered North America during MIS 6, ~195-135 ka, and then again at ~45-21 ka (Froese et al, 2017).…”

Initial Human Colonization of the Americas, Redux

“…Why should the Americas be unique? Many mammal species crossed Beringia in multiple immigration waves during cold periods of the Pleistocene (Salis et al 2020). Why not hominins, too?…”

An age-depth model and revised stratigraphy of vertebrate-bearing units in Natural Trap Cave, Wyoming

“…DICARB age determinations have been questioned (Reuther and Gerlach, 2005), though their incorporation into larger datasets used in Bayesian models may still have utility (Hamilton and Krus, 2018). Twenty-two of those ages have been referred to in publications (Shapiro, 2004;McKay, 2008;Williams, 2009;Salis et al, 2020;Perri et al, 2021;Salis et al, 2021;Table S1). LLNL Determinations 2015-2018: Fifty-eight (including two inter-and two intralab replicate samples) AMS 14 C ages were determined from NTC specimens at the Lawrence Livermore National Laboratory CAMS facility (LLNL; Table S1).…”