Genetic diversity in the Siberian jay Perisoreus infaustus in fragmented old-growth forests of Fennoscandia

The Siberian jay Perisoreus infaustus is a bird inhabiting old-growth conif erous taiga Forests. It has recently declined in numbers in Finland mainly because of habitat fragmentation. Distant mtDNA lineages from Taimyrian Pen insula (subspecies P. i. monjerensis) and middle Yenisei valley (P. i. rogo sovi) have diverged From Fennoscandian (P. i. infaustus) lineage ca 610000 yr ago. The estimated time to the most recent common ancestor for Fennoscan dian population (78000 yr) coincides with the beginning of the Weichselian ice age. Within Fennoscandia, the observed distribution of pairwise genetic distances followed the expected distribution of an expanding population re flecting the postglacial history rather than the present day situation of t he Siberian jay, Mitochondrial control region sequences showed that among 6 5 Fennoscandian individuals the most common haplotype (40%) was Found in al l but two populations. Genetic structuring (phi (ST) = 0.111) was clear wit hin the Fennoscandian population. This may be attributable to low intrinsic natal dispersal. In an isolate of western Finland, nucleotide diversity wa s significantly lower than in P. i. infaustus populations of the continuous distribution area. We suggest that isolation by habitat fragmentation in m odern landscapes may effectively reduce gene flow below the level occurring in natural conditions. Thus, Siberian jay isolates with limited number of individuals would be highly vulnerable to loss of genetic variation or even to extinction by demographic or environmental stochasticity.