Mito-nuclear discordance in a genus of darkling beetles (Coleoptera: Tenebrionidae: Dailognatha ) reveals both incomplete lineage sorting and introgression driven by complex island paleogeography

Abstract Phylogenetic studies of insular radiations have traditionally relied on mitochondrial DNA, yet the increasing availability of genomic datasets has revealed numerous cases of phylogenetic discordance between mitochondrial and nuclear markers across animal taxa. The present study focuses on the Aegean Dailognatha, a group of six predominantly insular darkling beetle species. The evolutionary history of the group was assessed using 1,610 nuclear protein-coding loci and mitochondrial genomes obtained from low-coverage WGS, which supported the existence of mito-nuclear discordance in both major clades (Clades A and B). The phylogenetic conflict observed in Clade A was associated with pervasive incomplete lineage sorting (ILS), while that in Clade B with introgressive hybridisation, both presumably resulting from the complex palaeogeographic history of the Aegean archipelago. Specifically, the formation of the Mid-Aegean trench coincided with three temporally clustered speciation events and likely played a key role in generating the observed pattern of ILS. An additional cladogenetic event coincided with the Messinian Salinity Crisis, during which hybridisation between D. hellenica and D. quadricollis likely occurred too. Overall, this study highlights the role of complex palaeogeographic dynamics in promoting both ILS and introgression within insular radiations, suggesting that mito-nuclear discordance may be more widespread in such systems than currently appreciated.