ANCIENT DNA FROM ALASKA'S EXTINCT PLEISTOCENE MUSK OXEN: PHYLOGENETICS AND POPULATION DYNAMICS REVEAL A UNIQUE PALEOENVIRONMENTAL HISTORY

Patterns and timing of megafaunal migrations and diversification in Beringia and Alaska during the Pleistocene were complex, and reflective of paleoenvironmental trends. Ancient DNA from radiocarbon-dated specimens provides data on the population dynamics and phylogenetic affinities of megafauna including bison, mammoths, and wapiti, which, along with plate tectonic and marine isotopic climate reconstructions, helps to build a robust and intricate picture of the Arctic world during the Quaternary. Comparisons between species, additionally, reveal even finer scale fluctuations in environmental conditions and biomes, and asynchrony in the migration and range dynamics of different herbivores. These dynamics and phylogenetic relationships are inferred from DNA sequences obtained from ancient sub-fossil bones, with powerful Bayesian statistical models that are used to estimate phylogenetic or family-tree relationships among individual specimens, population size and whether a population was growing or declining, and to identify genes that may have been under selective evolutionary pressure by modeling rates of molecular change over time.

I tested the hypothesis that musk ox migratory patterns, population dynamics, and rates of molecular evolution during the last 50,000 years were similar to those observed in other megaherbivores during the same time period. The results, in the form of new ancient DNA sequence data for two dozen specimens, provide insight into the population dynamics of the Alaskan musk oxen, and add a novel layer to the complex Quaternary history of Alaska and Beringia. Understanding the history of megafaunal migrations and habitat variability across Beringia over the past 50 thousand years adds to our understanding of the potential differential impacts climatic change may have on organisms that ostensibly occupy similar niches, in the present day and in predictions about the future.