Abstract: Vicariance and dispersal are fundamental biogeographical processes driving the distribution and diversification of species across space and time. This study examines the diversification and origin of some Hydropsyche lineages in the Aegean Archipelago by assessing three biogeographic hypotheses: a vicariance model driven by historical fragmentation, a dispersal model involving colonization across sea barriers, and a mixed model combining both processes. We reconstructed the cladogenesis for species located among island and mainland, estimated divergence times in relation to major paleogeographical events, and examined patterns of island endemism and their distribution. Phylogenetic and time-estimate analyses of mitochondrial cytochrome oxidase subunit I (COI) sequences revealed eight extant lineages exhibiting consistent inter-lineage genetic divergences exceeding 2.5%. These findings suggest a relatively recent diversification history, with primary speciation events during the late Plio-Pleistocene. Widespread species are consistent with a dispersal-driven model because their shallow Pleistocene divergences and large geographical ranges are compatible with recurrent colonization, whereas the geographically restricted island endemics are more consistent with a mixed model (vicariance and dispersal), with confined distributions. Overall, the recovered phylogenetic patterns do not show evidence for an ancient Miocene-vicariance model.

Key words: phylogenetics, caddisflies, biogeography, phylogeography, Pleistocene