Abstract

Genetic diversity in three taiga specialists — the Siberian tit (Parus cinctus), the Siberian jay (Perisoreus infaustus) and the Siberian flying squirrel (Pteromys volans) — was assessed by comparing DNA sequence variation across the mitochondrial control region and allele frequencies of microsatellites from samples collected from Fennoscandia and Siberia. Population sizes of these species have declined in association with fragmentation and loss of suitable forest habitat due to modern forestry practices in Fennoscandia. The red squirrel (Sciurus vulgaris) served as a reference for the flying squirrel.

Genetic differentiation among species studied ranged from a panmictic population in the Siberian tit to that of the strong differentiation of populations (θ_ST = 53%) in the flying squirrel in Finland. MtDNA and microsatellite data, together with assignment studies, showed the Siberian jay population to be significantly genetically structured and supported the existence of a metapopulation like structuring in Fennoscandia. Division of genetic variation among flying squirrel populations along the ancient shoreline of the Littorina Lymnea Sea stage of the Baltic Sea (7000 BP) and two geographically associated branches in the minimum spanning network supported a two-way colonisation history for the species. The Finnish inland appears to have been colonised from the east in association with the arrival of Norway spruce. At the same time, Coastal Finland was colonised from the south-east through the Karelian Isthmus. Gene flow of the species appeared female biased and restricted. Species exhibiting more restrictive dispersal characteristics and habitat requirements possessed stronger population genetic structure than those with opposite characteristics.

Growth or contractions in population size leave characteristic signatures in mtDNA that can be studied by comparing different sequence diversity estimates among populations. I applied this method to the species studied. Significant differences in nucleotide diversities indicated restrictions in gene flow among populations in all species studied. Half of the Siberian jay populations gave a signal of population size bottleneck.

All the species studied showed differences in their population genetic structures across their entire distribution ranges consistent with the multirefugia model, most likely to be attributable to differences in their ecological characteristics and Pleistocene histories.