Mitogenomic insights into the speciation and evolutionary history of the stag beetle genus Hexarthrius (Coleoptera: Lucanidae)

The genus Hexarthrius Hope, 1842, a prominent member of the family Lucanidae, is widely distributed across southern Asia and includes some of the largest stag beetle species in the world. This study presents the first mitogenomic phylogeny for Hexarthrius and its related genera, using complete mitogenomes from all recognized Hexarthrius species and representatives of all known related genera; 23 mitogenomes are reported here for the first time. We identified two novel mitochondrial gene rearrangements in Hexarthrius and its relative genus Rhaetulus Westwood, 1871, with implications for mitogenome evolution in Lucanidae. Phylogenetic inference and molecular dating recover Hexarthrius as monophyletic and subdivided into two well-supported clades: a Himalayan clade and a Tropical clade, which diverged approximately 8.9 million years ago. Rhaetus Parry, 1864 is inferred as the sister group to Hexarthrius , whereas Rhaetulus occupies a basal position within the larger Hexarthrius clade. Ancestral-area and morphological reconstructions indicate a complex history of vicariance and dispersal associated with uplift of the Hengduan–Himalayan region and subsequent island isolations. These results clarify species relationships, biogeography, and morphological evolution within this emblematic beetle lineage.