Detection of the ongoing sorting of ancestrally polymorphic SINEs toward fixation or loss in populations of two species of Charr during speciation

The FokI family of short interspersed repetitive elements (SINEs) has been found only in the genomes of charr fishes (genus Salvelinus). In an analysis of the insertion of FokI SINEs using PCR, we characterized six loci at which FokI SINEs have been inserted into the genomes of Salvelinus alpinus (Arctic charr) and/or S. malma (Dolly Varden). An analysis of one locus (Fok-223) suggested that a sister relationship exists between S. alpinus and S. malma and the SINE at this locus might have been inserted in a common ancestor of these two species, being fixed in all extant populations examined. By contrast, SINEs at two other loci (Fok-211 and Fok-206) were present specifically in the genome of S. alpinus, with polymorphism among populations of this species. Moreover, the presence or absence of the SINEs of the other three loci (Fok-214, Fok-217, and Fok-600) varied among populations of these two species. The most plausible interpretation of this result is that SINEs, which were ancestrally polymorphic in the genome of a common ancestor of these two species, are involved in an ongoing process of differential sorting and subsequent fixation in the various populations of each species.