Species delimitation in the Aleochara fucicola species complex (Coleoptera: Staphylinidae: Aleocharinae) and its phylogenetic relationships

To assess the accuracy of species delimitation and phylogenetic relationships of the Aleochara fucicola species complex, we performed molecular phylogenetic analyses. Detailed micromorphological characters were also examined using scanning electron microscopy (SEM). The molecular data set included two mitochondrial (COI and COII) and three nuclear protein‐coding genes (CAD, EF1‐α and wg) for 19 populations of five species. Significant discordance was found between mitochondrial and nuclear gene trees. Two species, A. puetzi (Assing) and A. segregata Yamamoto and Maruyama, were not separated in the mitochondrial gene trees, but clearly were differentiated in the nuclear and concatenated gene trees. The SEM data also supported the separation of these two species, but an analysis of genetic divergence data did not. Adaptation to extremely harsh environments might reduce morphological variation in the A. fucicola species complex during the colonization of seashores. We present a multilocus phylogeny of the species complex. It suggests that the ancestor of the A. fucicola species complex occurred along the southern coasts of Northeast Asia, followed by dispersals to northern coasts.