Craniometrical variability in insular populations of brown bear (Ursus arctos, Carnivora) from Hokkaido, Sakhalin and South Kurils

Abstract

The morphometrical analysis of 84 skulls of adult males of Ursus arctos from islands of the southern part of the Okhotsk Sea has revealed differences between brown bears from Hokkaido and South Kurils (U. a. yesoensis) and bears from Sakhalin, Shantar Islands and adjacent part of Asia (U. a. beringianus). The analysis has revealed craniometrical features of bears from three genetically different groups from Hokkaido and has shown similarity of bears from South Kurils (Iturup I., Kunashir I.) with bears of the eastern genetic group (B) from Hokkaido. The differentiation of bears into groups is mainly caused by the variation of width of the cerebral part and the basis of the skull and of the jaw height. Bears from Sakhalin are close to the continental ones, but have the smaller sizes and narrower skull in the postorbital area. The morphometrical data do not correlate with the supposed time of immigration of different groups of the brown bear to Hokkaido. Most likely, these data are defined by local adaptations of the studied populations. In our work, quantitative (informational) characteristics of the morphological (morphometrical) diversity of skulls of bears of different subspecies, important for comparative studies, are defined for the first time. Skull of U. a. yesoensis is characterized by a low variety in comparison with those of U. a. beringianus and other subspecies. The hypothesis about rather high morphological specialization of U. a. yesoensis, U. a. beringianus and U. a. piscator in comparison with U. a. arctos and U. a. collaris is formulated.