Faunal response to abrupt climate change: the history of the British mammal fauna from the Lateglacial to the Early Holocene

Rapid changes in climate are known to be drivers of profound ecosystem change and adaptive evolution. Repetitive and abrupt switches between glacial and interglacial conditions are strongly associated with range shifts, isolation in refugia, extinctions, local extirpations, re-colonisation events, demographic oscillations and repeated bouts of secondary contact in both flora and fauna. This study utilises a synthesis of ancient DNA and both 2D and 3D geometric morphometrics to examine phylogenetic, ecomorphological and population-level responses to abrupt climate change in British mammals. The investigation focuses on a period of significant climatic variability; the closing stages of the last (Devensian) glaciation into the current Holocene interglacial. Four broad alternating cold and warm episodes are recognized in Britain – the end of the Dimlington Stadial, the Lateglacial Interstadial, the Younger Dryas Stadial and the Holocene Interglacial. Three species with differing ecologies and life history traits were selected in order to look for common trends or individualistic responses: common vole (Microtus arvalis), Eurasian beaver (Castor fiber) and the European wildcat (Felis silvestris silvestris).

Geometric morphometrics was shown to be a highly effective tool, both with which to discriminate between morphologically similar species using isolated molar teeth, and with which to identify subtle form changes in tooth morphology that can be related to climate. Whole mitogenomes and single coding and non-coding mtDNA sequences were successfully obtained, in all cases representing the oldest DNA yet sequenced from these species. A common geographical origin was identified for all species as the north-west coast of Europe. Evidence for population continuity over the Younger Dryas cold interval was uncovered for M. arvalis and C. fiber and was associated with a possible micro-refugial area in the south-west of England. Levels of genetic diversity and the degree of phylogenetic and population substructure could be tentatively attributed to the individual dispersal capabilities and ecological preferences of different species.

Overall, this study uncovered formerly unknown population histories from ancient British mammal species and highlighted the huge potential of ancient DNA and geometric morphometrics for unravelling the Late and Postglacial history of the British mammal fauna.