Mitochondrial DNA sequence divergence among some west European brown bear (Ursus arctos L.) populations. Lessons for conservation.

We used the polymerase chain reaction and nucleotide sequencing to study mitochondrial DNA (mtDNA) genetic variability of brown bears (Ursus arctos) belonging to some western European populations. Demographic decline and isolation have apparently shaped genetic variability within and between populations. Small relict bear populations were apparently monomorphic and fixed for different mtDNA haplotypes. Genetic relationships among mtDNA haplotypes suggested the existence of a phylogeographic structure. We discuss the possible roles of historical and demographic factors in determining the observed genetic patterns. The low genetically effective size of the studied brown bear populations points to risks of continuing future loss of gene diversity and increase in inbreeding. Artificial gene flow through restocking could alleviate inbreeding depression in small isolated brown bear populations, and mtDNA phylogeographic relationships may provide a framework for their genetic management.