Postglacial colonisation and diversification of the Jungle Crow (Corvus macrorhynchos) in its north-eastern frontier as revealed by morphological analysis

Abstract

The Jungle Crow (Corvus macrorhynchos) is a widespread species in Asia that underwent remarkable postglacial recolonisations during the Pleistocene and Holocene. In order to better understand the pattern of its settling and diversification, we investigated the morphological differences among adult Jungle Crow samples obtained from locations in northern Japan and the Russian Far East: Hokkaido, Sakhalin Island, the continental seaboard adjacent to the Tatarsky Strait and the region to the west of the Sikhote-Alin Mountains. We studied four cranial measurements and five bill measurements, as well as body mass from 195 samples. We found clear differences among most populations for both males and females when the various characteristics were observed, especially on Hokkaido and Sakhalin Island; crows from Hokkaido had larger bills and lighter body mass. The differences between the Hokkaido and Sakhalin populations correspond to Bergman’s and Allen’s rules, but this was not the case with the longitudinal cline revealed among the three populations from the Russian Far East. In conclusion, our results suggest that La Pérouse Strait separates two assumed recolonisation movements, the first being along the mainland via Ussuriland to Sakhalin and the second along the Japanese Archipelago to Hokkaido. It is evident that this strait is a more effective barrier between Jungle Crow populations than either the Tatarsky Strait or the Sikhote-Alin mountain range.