Ancient DNA perspectives on North American cervids identify dispersal waves and fluctuations in diversity

North American fauna experienced major changes over the last two million years. Glacial cycles, animal migrations, peopling waves, and, more recently, European colonisation caused demographic fluctuations, divergence, and extinctions. Caribou, moose, wapiti, white-tailed and mule deer are the five extant cervids in Northern America, with unique colonisation patterns and conservation statuses. Here, we used DNA analysis of ancient, historical and modern individuals of these Cervidae to retrace evolutionary processes through time. Our results suggest rapid expansion of moose and wapiti following their arrival on the continent, with the latter showing a subsequent loss of diversity. We show that eastern Canada caribou share ancestry with a 30kya sample from western Canada. Data also give weight to rapid diversification in Odocoileus species resulting in incomplete lineage sorting and mito-nuclear discordance. Our results exemplify the utility of chronological sampling to gain a better understanding of how external pressures drive genomic changes.