Species delimitation in the genus Stenaptinus (Coleoptera: Carabidae: Brachininae) from Korea using quantitative morphological and molecular data

The genus Stenaptinus has long faced taxonomic challenges due to high morphological similarity among species and a reliance on color patterns for identification. In this study, we aimed to accurately identify Stenaptinus javanus recorded in Korea and a population of Stenaptinus with a new color pattern found on the southern islands of Korea. By comparing the endophallus of male genitalia, we reidentified the Korean S. javanus as S. marginicollis and the new population from the southern islands of Korea as S. occipitalis. However, since S. occipitalis is classified into subspecies based on color variation, we conducted mitochondrial DNA analysis of the CO1 gene and performed principal component analysis (PCA) on quantitative color patterns to accurately confirm the identity of this group. Mitochondrial DNA analysis showed that this group is identical to S. occipitalis jessoensis recorded in the Korean Peninsula, but PCA of color patterns revealed a clearly separate cluster. To understand these results, we analyzed environmental variables affecting melanization in S. occipitalis. We found significant correlations with latitude, temperature, and humidity. This suggests that S. occipitalis may exhibit melanization differences depending on environmental conditions. Therefore, the new population in the southern islands of Korea can be interpreted as resulting from reproductive isolation and environmentally induced melanization.