well, the picts seem to have become the Highlander folks while the lowlander Scots are descendents of the Scotti tribe that came over from Ireland around the 1st century.
This is possible, but not sure, since the Scotti moved to the islands in the Irish Sea, spreading until their new kingdom included parts of the western Scottish tereritory. Eventually the kingdom lost possession of the islands, and remained purely in Scotland. This transitional kingdom including the islands was called Dalriada, which has long seemed to me one of the loveliest names of any state in the British Islands.