Climate-driven ecological changes through the last glacial period: innovations in plant ancient DNA and stable isotope palaeoecology

Abstract

The impact of climate-driven ecological changes can be understood by reconstructing the effects of past climate variation on the flora and fauna. This thesis develops and applies new methods for inferring the history of the graminoid-dominated steppes of the northern Holarctic and Patagonia as they declined during the end of the Last Glacial Period (25,000–10,000 years ago). Stable nitrogen isotope data are used to argue for the pivotal role that landscape moisture played in the decline of the Pleistocene megafauna, and a new method for inferring relative changes in plant-available moisture from herbivore collagen isotopic measurements is developed. Experimental methods for working with botanical ancient DNA are presented, tested, and used to explore the taxonomy and evolutionary histories of three ancient plant species, ultimately yielding the two oldest known draft chloroplast genome sequences, dating to between 50,000 and 80,000 years ago. The results confirm the strongly-reticulated phylogenies characteristic of plants evolved to employ great plasticity as an adaptive ability, even with minimal sexual reproduction. All new genetic methods are tested with the aid of a newly designed program SimWreck, which simulates sequence data with the known characteristics of ancient DNA.