Survival and divergence in a small group: The extraordinary genomic history of the endangered Apennine brown bear stragglers

Significance A small and relict population of brown bears lives in complete isolation in the Italian Apennine Mountains, providing a unique opportunity to study the impact of drift and selection on the genomes of a large endangered mammal and reconstruct the phenotypic consequences and the conservation implications of such evolutionary processes. The Apennine bear is highly inbred and harbors very low genomic variation. Several deleterious mutations have been accumulated by drift. We found evidence that this is a consequence of habitat fragmentation in the Neolithic, when human expansion and land clearance shrank its habitat, and that retention of variation at immune system and olfactory receptor genes as well as changes in diet and behavior prevented the extinction of the Apennine bear.