Genomic history of Italian brown bears

Apennine bears are a critically endangered population of approximately 50 Italian brown bears that live in the central Apennine Mountains. Apennine bears (Ursus arctos marsicanus) are separated from other bear populations by several hundred kilometers. Andrea Benazzo et al. (pp. E9589–E9597) explored genomic variation and evolutionary divergence in Apennine bears. The authors sequenced the full genomes of six Apennine bears and six other European brown bears. The authors estimate that Apennine bears were separated from other brown bears during the Neolithic Period, resulting in a 40-fold decline in the Apennine population; Apennine bears may have become isolated due to human expansion and land clearing, the authors suggest. The genetic analysis indicates that Apennine bears are highly inbred with a complete loss of variation in the mitochondrial genome and along long stretches of the nuclear genome. Random drift appears to have fixed several deleterious mutations, but also led to unique features such as small size, distinctive cranial morphology, and reduced aggressiveness, compared with other bears. In combination with a lack of competitors, a nearly vegetarian diet, and low aggressiveness, peaks of high variation in genes associated with the immune and olfactory systems may have helped Apennine bears avoid extinction, according to the authors.