Population genetics of the Siberian flying squirrel (Pteromys volans) in Finland using whole mitochondrial genomes

Abstract

The European populations of the Siberian flying squirrel (Pteromys volans) have been steadily declining for decades and in 2019, Finland’s flying squirrel population (representing the western edge of the global distribution) has even been red-listed as ‘Vulnerable’. In this thesis, I present first insights into the population genetics, population structure and phylogeography of the Siberian flying squirrel across their entire Finnish distribution using whole mitochondrial genomes. Furthermore, I investigate the possible geographical origin of this ex-situ population by comparing cytochrome b sequences of an individual from the Zoo in Riga, Latvia, with those of in-situ Siberian flying squirrels across their global distribution.

In total, 55 new whole mitochondrial genomes (16,511 bp) for the Siberian flying squirrel were sequenced: 52 from Finland, 2 from Estonia, and 1 from the ex-situ population.

Genetic diversity of the mitochondrial genome is very low for the Finnish population, with a nucleotide diversity (π) of 0.00032 (±0.00003) and only max. 19 nucleotide differences between all 52 individuals. The Finnish population is structured into three haplotype clusters. Two of them correlate geographically with either the northeastern or southwestern half of the Finnish distribution and show strong signs of population expansion, and the third may represent the ancestral Siberian flying squirrel lineage. This structure was likely shaped by post-glacial processes, with the extensive lake network in ‘Lakeland’ acting as a significant geographical barrier. Both Early Holocene and Late Holocene colonization scenarios are possible. The low genetic variation limits the adaptive potential of Finland’s Siberian flying squirrels, potentially making them less resilient to climate change and more susceptible for diseases. For long-term conservation, it is crucial to sustain the standing variation left in the population.

For the ex-situ individual, the cytochrome b haplotype network revealed closest relation to in-situ populations around northeastern China and southeastern Russia, indicating that at least one female founder of Riga’s Zoo population originated from the Far East phylogenetic clade. Thus, ex-situ genetic variation could differ greatly to that of European in-situ populations, which belong to the Northern Eurasia clade.