The genetic structure of Squalidus multimaculatus revealing the historical pattern of serial colonization on the tip of East Asian continent.

Separated river systems could create confluences via two geological processes, estuary coalescence in response to decreasing sea levels and headwater capture, allowing primary freshwater species to disperse across rivers. Squalidus multimaculatus, is an endemic and primary freshwater species restricted to the southeast coast of the Korean Peninsula. The distribution of this species is unique, given that other congeneric species, including its closely related S. gracilis majimae, as well as other cyprind species are observed throughout the peninsula except for the east coast. Phylogeographic analyses were conducted using three mitochondrial loci to identify the origin of S. multimaculatus and the historical pathways of dispersal. A strong phylogenetic affinity between S. multimaculatus and S. g. majimae and the genetic structure among populations indicated that S. multimaculatus originated from the eastward colonization of the common ancestor between S. g. majimae and S. multimaculatus via headwater capture through fault zones within successive mountain range. Following colonization, the ancestral S. multimaculatus likely migrated towards north via estuary coalescence along a well-developed continental shelf. Our study was the first empirical attempt providing insights into how freshwater organisms dispersed to the southernmost tip of East Asia, despite the potential loss of such historical imprints with anthropogenic interference.