THE SALMON SMAI FAMILY OF SHORT INTERSPERSED REPETITIVE ELEMENTS (SINES) - INTERSPECIFIC AND INTRASPECIFIC VARIATION OF THE INSERTION OF SINES IN THE GENOMES OF CHUM AND PINK SALMON

The genomes of chum salmon and pink salmon contain a family of short i nterspersed repetitive elements (SINEs), designated the salmon SmaI fa mily. It is restricted to these two species, a distribution that sugge sts that this SINE family might have been generated in their common an cestor. When insertions of the SmaI SINEs at 10 orthologous loci of th ese species were analyzed, however, it was found that there were no sh ared insertion sites between chum and pink salmon. Furthermore, at six loci where SmaI SINEs have been species-specifically inserted in chum salmon, insertions of SINEs were polymorphic among populations of chu m salmon. By contrast, at four loci where SmaI SINEs had been species- specifically inserted in pink salmon, the SINEs were fixed among all p opulations of pink salmon. The interspecific and intraspecific variati on of the SmaI SINEs cannot be explained by the assumption that the Sm aI family was amplified in a common ancestor of these two species. To interpret these observations, we propose several possible models, incl uding introgression and the horizontal transfer of SINEs from pink sal mon to chum salmon during evolution.