Discovery of a genetically distinct lineage in medaka species within Lake Towuti in central Sulawesi

Oryzias marmoratus and Oryzias profundicola in Lake Towuti in Sulawesi are considered to have experienced ancient admixture with a lineage phylogenetically close to the extant O. marmoratus in Lake Lantoa. However, the admixture may be ongoing because these lakes are currently connected to each other by rivers. In this study, we examined population genetic structures of O. marmoratus and O. profundicola in Lake Towuti and adjacent lakes. Mitochondrial and microsatellite analyses revealed that O. marmoratus and O. profundicola in Lake Towuti are generally clearly separated from O. marmoratus in Lake Lantoa. However, we found one O. marmoratus individual in Lake Towuti shared a mitochondrial haplotype and a large fraction of ancestry with the Lantoa O. marmoratus. The discovery of this Lantoa-type individual in Lake Towuti suggests that either dispersal of individuals from Lake Lantoa to Lake Towuti is ongoing, or that there is another unknown population within Lake Towuti that originated from ancient admixture.