Cryptic diversity on Apennine sky islands: evolutionary history of flea beetles of the Psylliodes springeri (Coleoptera, Chrysomelidae) species complex

High-altitude environments on isolated mountain peaks harbor unique biodiversity, offering natural laboratories to study past climate change impacts on speciation. In Europe, the Italian Apennines stand out for their high insect endemism, including the micro-endemic flea beetles Psylliodes springeri Leonardi, 1975 and the more widely distributed P. biondii Leonardi, 1975, which shows a morphologically distinct population on the Maiella Massif. Using species delimitation methods, multispecies coalescent models, and a multilocus molecular approach, we identified key phylogenetic lineages and estimated the timing of cladogenetic events shaping this diversity. Phylogenetic analysis confirmed the monophyly of the springeri species complex, consistent with their morphological and ecological similarities. Large genetic distances and lineage sorting in both mitochondrial and nuclear gene trees distinguish the Maiella population as a separate lineage from P. biondii. Genetic differentiation between these 2 lineages matches the interspecific distance observed between P. biondii and P. springeri. Molecular dating places their divergence in a short time frame during the Early Pleistocene, approximately 2 million years ago, likely driven by glacial–interglacial cycles, which isolated populations and triggered divergence. While P. springeri and the Maiella lineage remained confined to their respective single massifs, P. biondii exhibited a broader distribution, suggesting distinct ecological responses to climate fluctuations. This study underscores how climate-driven isolation has fueled rapid speciation in the Sky Island beetles of the central Apennines, shedding light on the evolutionary history of the largely unexplored biodiversity of high-altitude southern European ecosystems. Future studies may offer further insight into the evolutionary and taxonomic status of the Maiella lineage.