Postglacial colonization and population genetic relationships in the Pinus contorta complex

To explore the evolutionary relationships among the subspecies of lodgepole pine (Pines contorta Dougl. ex Loud.) and the possible existence of a northern glacial refugium for Pinus contorta Dougl. ex Loud. subsp. latifolia Engelm. and a coastal refugium for Pinus contorta Dougl. ex Loud. subsp. contorta, 31 populations were analyzed using RAPD markers to determine whether a pattern of isolation by distance exists. A total of 52 markers from 10 primers were scored. A significant pattern of isolation by distance was detected when all 31 populations were analyzed together and for the 19 populations of subsp. latifolia. A phylogenetic tree constructed from all 31 populations does not show an unambiguous division of the subspecies of P. contorta into distinct clades. Our results provide no support for the separation of lodgepole pine into various subspecies and show that the subspecies of lodgepole pine have not been sufficiently isolated from one another for a large amount of genetic divergence to occur between them. For subsp. latifolia, the pattern of isolation by distance is consistent with the hypothesis of a single refugium south of the glacial maximum with population expansion following glacial retreat. The amount of genetic distance and the pattern of differentiation in populations of subsp. contorta suggest a more complex history associated with fluctuation in ocean levels and glacial margins.