Phenetic analysis of skull reveals difference between Hokkaido and Sakhalin populations of the jungle crow Corvus macrorhynchos

Jungle Crow Corvus macrorhynchos Wagler, 1827 is widely distributed in East Asia, but no so far to the North. It requires dense forest and rather mild climate for breeding, therefore during the ice ages they vacated around the Japan Sea Rim in favor of southern refuge located around the East China Sea. After the Last Glacial Maximum, Jungle Crows began to recolonize the north-eastern Asia presumably via two routes: one via the Japanese Archipelago, and the other via Ussuriland (Nechaev, 1971). This might lead to appearance of two subspecies: C. m. mandshuricus and C. m. japonensis. We attempted to find out any new features in purpose to reveal a place where these two recolonization movements have encountered. Detailed analysis of delicate differences in the skulls of five populations of Jungle Crow from Primorsky, Khabarovsky, Amur regions, Sakhalin and Hokkaido islands was conducted. Based on 197 cleaned skulls, 88 from females and 109 from males, we determined incidence frequencies for 10 characters which provide adaptations of the species’ strong bill. 7 features were revealed in juveniles only, frequency of the two others change during the life, and for the remaining stay stable. No difference between males and females was found. For frequencies of pinhole in parasphenoid and septum shape in orbital cavity, we found a significant difference between Hokkaido and Sakhalin populations, while for all other characters studied and between other populations, differences were not significant. The results obtained do not correspond neither to subspecies subdivision for C. m. mandshuricus and C. m. japonensis, nor to previous genetic data by mitochondrial cytochrome B gene which revealed an island and mainland groups of haplotypes (Kryukov et al. 2012). In the same time, as a result of using the phenetic (nonmetric morphological) study on the skull, we show that two movements encountered at the La Perouse Strait. Furthermore we found an indirect evidence for current introgression between Sakhalin and Hokkaido populations.