Dispersal of Pleistocene horses across Beringia
Climate shapes landscape connectivity, habitat and food availability, and represents a major driver of megafaunal population dynamics. Here, we apply advanced genomics and isotope profiling on fossil horse (Equus spp.) remains from across Beringia as a model for illustrating the profound impact of climate on megafaunal populations. The dispersal of Pleistocene horses native from North America  during past glaciations left enduring genetic traces across Eurasia until the Holocene. Between 46-16 ky BP, Eurasian horses traversed back across the Bering Land Bridge multiple times. The advance and coalescence of continental and Cordilleran glaciers, however, hindered dispersal to interior North America, leading to the evolution of isolated lineages with minimal Eurasian influence. As climate warmed and became wetter 16-10 ky BP, sea level rise flooded the Bering Land Bridge, disconnecting Asian and American horse populations, and opened an ice-free corridor connecting Beringia and mid-continental America. Despite this opportunity for genetic exchange, habitat fragmentation restricted mobility and food availability within that corridor, leading to local demographic collapse. Our integrated genetic, isotopic and Indigenous scientific analyses offer insights for the conservation of modern Arctic grazers amidst ongoing climate warming.