Assessing the Impact of Arctic Glacial History on Walrus Genetic Structure and Diversity Through Time Using Ancient Mitochondrial DNA

Open Access
Cousar, Michael Christopher
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Dr Beth Shapiro, Thesis Supervisor
  • Stephen Wade Schaeffer, Honors Advisor
  • ancient DNA
  • mitochondrial DNA
  • walrus
  • phylogenetic analysis
  • molecular biology
  • glacial history
  • population genetics
The emergence of ancient DNA (aDNA) research in 1984 has resulted in a number of studies exploring evolutionary history of plant and animal species incorporating genetic data isolated from ancient and historic remains. Phylogenetic studies using aDNA are aimed at determining the driving force behind changes in genetic diversity within populations. Here, we examine the phylogenetic history of walruses using a mitochondrial DNA analysis. The walrus (Odobenus rosmarus) is currently divided into three subspecies based on their geographic distribution: Atlantic (O. r. rosmarus), Pacific (O. r. divergens), and Laptev Sea (O. r. laptevi). The recent discovery of ancient walrus fossils on Herschel Island in the Yukon Territory, Canada, provides an opportunity to incorporate these samples in an overall genetic analysis of walrus, to determine whether past glacial cycles had an effect on walrus diversity. In this study, mitochondrial DNA from ancient Herschel Island, modern Pacific, ancient Atlantic walrus samples was extracted and sequenced. The sequence information was combined with data from another study to produce phylogenetic trees and haplotype networks. While our results are inconclusive with regard to the evolutionary relationship between modern walruses and the Herschel Island specimens, we found strong support for two distinct Pacific walrus mitochondrial clades. The results will be used in a larger study that will explore walrus phylogenetic history in greater detail.