Phylogeography of Scymnus posticalis (Coleoptera: Coccinellidae) in East Asia: genome-scale insights into Neogene divergence and geographic isolation shaping population structure

Abstract Scymnus posticalis Sicard, 1912, an important predatory ladybird beetle, is widely distributed throughout East Asia. However, the impact of geographic isolation on their phylogeography remains poorly understood. To elucidate the phylogeographic structure among S. posticalis populations in East Asia, identify the impacts of climate change and geographic isolation on population structure, and reconstruct the species’ population demographic history, we employed whole-genome resequencing combined with an optimized MaxEnt niche model. Our genomic analyses clearly revealed that S. posticalis formed 7 distinct phylogeographic lineages, with significant genetic differentiation among these distinct lineages in East Asia. Divergence time estimation indicated that these lineages diverged sequentially from the late Oligocene to the late Miocene (27.40 to 7.19 Ma). The extent of lineage divergence exhibits a significant correlation with geographic distance, indicating that isolation by distance plays a key role in shaping the current phylogeographic patterns of S. posticalis. This study represents the first phylogeographic investigation of the genus Scymnus globally, and its findings fill a critical gap in phylogeographic research on Coccinellidae in Asia. Our findings contribute to a better understanding of how climate change and geographic barriers jointly influence the evolutionary processes in East Asian insects and provide a valuable framework for future studies on population differentiation, speciation, and phylogeography of montane insect taxa in this biodiversity-rich region.