Mitochondrial DNA analysis of the evolution and genetic diversity of ancient and extinct bears.

Abstract

Mitochondrial phylogeographic analyses of modern populations can be used to make inferences about the impacts of the last glacial maximum (LGM) and anthropogenic disruption on late Pleistocene and Holocene ancestral populations. However, it is becoming more and more evident that ancient DNA studies greatly augment traditional mtDNA studies based only on extant lineages, and can reveal more complex scenarios than those hypothesised from modern data alone. Ancient DNA studies allow us to trace historic and ancient gene flow through time, giving a dynamic temporal and geographic understanding of genetic diversity. This is particularly informative when molecular data can be coupled with environmental or chronological information (such as radiocarbon dated specimens) allowing links to be made between climatic or anthropogenic disruptions and the genetic response of populations or species. This PhD research used ancient DNA techniques to investigate a number of biogeographic scenarios in relation to the phylogeography of brown bears (Ursus arctos) in Europe (Chapter 2- 4) and across the Eurasian continent (Chapter 5) throughout the Late Pleistocene and Holocene periods. Similarly, a study of the genetic diversity and phylogeography of the extinct giant short-faced bear (Arctodus simus) in North America was undertaken (Chapter 6) to provide a comparison with the dynamic phylogeographic history of contemporaneous Beringian brown bears (Barnes et al., 2002). Additionally, the deeper evolutionary history of the extinct Tremarctine bears was investigated using a molecular approach (Chapter 7) in an attempt to clarify the phylogenetic relationships of this lineage which have remained unresolved by morphological analyses. The research presented in this PhD thesis reinforces the important role that ancient DNA can play in understanding the mtDNA population dynamics and movements of taxa in response to environmental or anthropogenic changes through time. It stresses once again that the use of modern data alone is likely to lead to over-simplified or inaccurate views of past evolutionary history. Ancient DNA studies such as those presented here allow us to develop a more complex understanding of Quaternary phylogeographic patterns in a small number of taxa for which a sufficient number of samples can be obtained, and may guide future research to determine if similar patterns exist for other less-well studied species.