Cranial distinctiveness in the Apennine brown bear: genetic drift effect or ecophenotypic adaptation?
Molecular studies highlighted a strong genetic affinity between the remnant and isolated
population of the Apennine brown bear and other southern European populations (Taberlet
& Bouvet, 1994; Randi et al., 1994). Despite this genetic closeness a recent morphometric
study (Loy et al., 2008) revealed a marked phenotypic distinctiveness of the Apennine
population, supporting the reinstatement of a distinct taxon (U. arctos marsicanus).
By building upon previous morphological analyses, we adopted geometric morphometrics
to better investigate skull morphology of the Apennine brown bear with reference to the
other, closely related south European populations.
Both skull shape and size differences confirmed the strong divergence of U. arctos
marsicanus. Particularly the Apennine bears are characterized by an enlargement of
supraorbital apophysis and a larger distance across the zygomatic arches. Furthermore,
our analyses highlighted a significant shape differences of the first upper molar in the
Apennine bears.
Our results suggest that the Apennine bears underwent a rapid morphological change
possibly driven by genetic drift and local selective pressures. Because the greatest
morphological differentiation is likely related to the muscles involved in mastication, we
hypothesize that local selective pressures might be related to a shift in food habits, with
highly reduced depredation and feeding on large carcasses in favour of vegetation and
hard mast (beech nuts and acorns).
These results suggest an adaptive distinctiveness of the Apennine bears, which should be
carefully considered in any management and conservation action addressed to this highly
endangered population. While more in-depth molecular studies are required to better
assess the taxonomic and genetic status of the Apennine brown bear population, our study
emphasises the importance of morphological analyses as a complementary tool for a more
thorough characterization of variation and divergence of endangered taxa.