PHYLOCHRONOLOGY: POPULATION GENETICS THROUGH SPACE AND TIME

The end-Pleistocene mammalian extinctions in North America ushered in newly assembled temperate faunas, most of whose members survive today. The Holocene witnessed climatic oscillations including warming and cooling events, which, although minor by Pleistocene standards, appear to have caused an evolutionary response of mammals at the population-genetic level. Observation of the morphological and genetic change exhibited by select mammalian species allowed us to explore evolution on a heretofore uninvestigated time scale, simultaneously providing more information than any modern geographic study and adding detailed genetic data to the paleontological perspective. Advanced molecular techniques permitted extraction of high quality DNA from fossils and, combined with sufficiently large samples, led to assembly of population genetic data that documented molecular evolution through space and time. Such phylochronologic analyses demonstrated a suite of evolutionary responses to climatic change that are determined by life history. While some species exhibit extreme genetic isolation and phenotypic plasticity, others exhibit enhanced gene flow and show evidence of selection across a large geographic scale. These responses indicate the breadth of evolutionary responses through the late Quaternary and imply dynamics between population structure and climatic change previously unimagined.