The preservation and postglacial history of ice age Holarctic beetles, as inferred from museum and ancient DNA

Degraded DNA can be recovered from specimens that are preserved in museums and the natural environment. Data generated from such DNA have provided valuable evidence for the assessment of a suite of biologically important questions. However, research of this nature is limited for invertebrate taxa, despite their diversity and ecological necessity. Using DNA data from dry-stored museum and permafrost-preserved ancient specimens, this thesis greatly extends the study of degraded DNA from invertebrates. The thesis focuses on two arctic ground beetle species (Amara alpina, Pterostichus brevicornis), which are abundant in museum collections and permafrost deposits.

A lack of data that characterises the preservation and potential of degraded beetle DNA, and thereby assessment of future possibilities for this emerging field, provided the impetus for the first three results chapters. Using two different sequencing approaches, the preservation of DNA in museum and ancient specimens was investigated. In addition, the taxonomic utility of DNA extracted from these specimens was assessed. These chapters demonstrate that DNA could be routinely recovered from museum specimens. DNA from ancient specimens could be recovered from A. alpina but not P. brevicornis. In most cases therefore, degraded DNA from these beetles could be used to address further questions.

The final two results chapters focus on the response of the two study species to a past period of climatically driven change, using DNA data from museum and ancient specimens. In these chapters, the mode of postglacial colonisation of Canada at the end of the last ice age was investigated. It was found that existing models of this process were broadly, but not wholly, correct. This may have implications for models of how beetles will respond to future climatic change.

Although some challenges lie ahead, this thesis demonstrates the potential for museum and ancient permafrost-preserved beetle specimens in future, DNA-based, large-scale investigations.