“Infinite” potential in beetle reticulate evolution: evidence for hybrid origin and secondary mitochondrial capture, with incidental intergeneric hybridization

Hybridization and introgression are increasingly recognized as important drivers of evolution, yet stabilized hybrid lineages remain poorly documented in insects. We investigated the origin of Eodorcadion oryx, a geographically restricted longhorned beetle endemic to central Mongolia, hypothesized to derive from hybridization between Eodorcadion exaratum argali and Eodorcadion kozlovi. Analyses of mitochondrial and phased nuclear sequences revealed pronounced mito-nuclear discordance, further contextualized by morphology, divergence-time estimates, and distribution. Mitochondrial data recovered E. oryx as a monophyletic lineage nested within a geographically restricted subset of E. kozlovi, exhibiting minimal divergence and complete haplotypic uniformity across individuals sampled over a decade. In contrast, nuclear alleles consistently affiliated E. oryx with E. e. argali, with only limited introgression from E. kozlovi, a pattern further supported by morphology. A quantitative ordination analysis (PCoA based on Gower distance) further confirmed that all three taxa form entirely distinct, nonoverlapping morphological clusters, reinforcing the qualitative diagnostic differences described above. Time-calibrated phylogenies revealed deep nuclear divergence within the complex (∼1.7 to 2.3 Ma), contrasting with substantially younger mitochondrial coalescence (∼0.52 to 0.73 Ma), whereas divergence estimates outside the focal clade remained broadly concordant between markers. Together, these results are consistent with a multistage scenario involving hybrid origin followed by geographically restricted secondary contact, resulting in near-complete mitochondrial capture and negligible nuclear gene flow. We additionally document a rare case of ongoing intergeneric hybridization between E. oryx and Humerodorcadion humerale impluviatum. This study documents stabilized hybrid ancestry in Coleoptera and highlights the dynamic nature of reticulate evolution in flightless insects.