A morphology-based revision and phylogenetic analysis of the Pterostichus macrogenys species group (Coleoptera, Carabidae) and implications for differentiation of the species group

The Pterostichus macrogenys species group is an endemic subterranean Japanese carabid clade that provides intriguing material for studying morphological differentiation, speciation and interspecific relationships. However, its diversity remains not fully explored. We investigated specimens from northern Tohoku District, an area where knowledge of this species group is notably limited. Our research led to the description of three new species: P. namahagesp. nov., P. kamurosanussp. nov. and P. atsumidakensissp. nov. We also updated distribution records for three known species: P. asahinus Habu & Baba, 1960; P. kitakamisanus Sasakawa, 2005; and P. chokaisanus Sasakawa, 2009. This report includes both the expanded distribution ranges of the known species and the discovery of a new sympatric species pair (P. chokaisanus and P. asahinus). We conducted a morphological phylogenetic analysis of all but one species, for which no male specimens were available, accounting for a total of 42 species within the group. The resulting phylogenetic tree implies that the initial differentiation of this species group originated on the Sea of Japan side, in the northern part of their current distribution, followed by dispersion to other areas and subsequent differentiation. Additionally, our findings indicate that sympatric species of varying body sizes are distantly related phylogenetically. These insights into the differentiation process align with regional distribution patterns of species-level diversity and sympatric sites.