Abstract
Even in species which are distinguishable by mainly internal structures or molecular data (e.g., cryptic species), external morphology could be useful for species identification. This paper describes the morphology and distribution of two species in Poecilus ‘samurai’ (Coleoptera: Carabidae) and tested the utility of external morphometrics for identification of cryptic species. The examination of the membranous parts of genitalia revealed that P. ‘samurai’ is composed of two externally similar species: P. sp. 1 (Hokkaido and Honshu) and P. sp. 2 (Hokkaido, Kyushu, Russia and Korea). With a focus on the identification of individuals from Hokkaido where the two species sympatrically occur, discriminant analyses based on measurements of ten external characteristics were performed between P. sp. 1 (Hokkaido) and P. sp. 2 (Hokkaido), and between P. sp. 1 (Hokkaido and Honshu) and P. sp. 2 (Hokkaido). In the former, all individuals were correctly classified into their own species, whereas in the latter, some individuals were incorrectly classified, suggesting that discriminant analyses using focal populations are more effective. A morphological phylogeny of five Poecilus species (including sp. 1 and 2) was provided, and the distribution pattern in the Japanese Archipelago was discussed.
