The dynamics of a changing Lutz spruce (Picea x lutzii) hybrid zone on the Kenai Peninsula, Alaska

We investigated the genetic makeup of Lutz spruce, a natural hybrid between white and Sitka spruce on the Kenai Penin-sula, Alaska. Microsatellites indicate 72% of individuals sampled had predominantly white spruce ancestry, whereas 14% had predominantly Sitka spruce ancestry; some individuals classified as white spruce had Sitka spruce plastid genotypes. As Picea mitochondria are maternally inherited and plastids are paternally inherited, it appears that white spruce was the ancestral seed parent of nearly all spruce on the western peninsula, whereas Sitka spruce alleles originated from pollen. Pollen records show that white spruce colonized the western peninsula <^>-8500 YBP from glacial refugium, whereas Sitka spruce arrived on the eastern peninsula <^>-4000 YBP after migrating up the Pacific coast. Our data suggest that Sitka spruce colonization west of the Kenai Mountains may have occurred not via seed dispersal but by long distance transport of wind-borne pollen and sub-sequent hybridization with established white spruce populations. Hybridization was an important mechanism that allowed Sitka spruce to expand the leading edge of its range in response to historical climate change. As the climate continues to warm, climate envelope modeling suggests Lutz spruce may ultimately displace white spruce on the western peninsula even as Sitka spruce is constrained to the eastern peninsula where it will continue to hybridize.

Automated summary

We studied the genetic composition of Lutz spruce, a hybrid between white and Sitka spruce in Alaska's Kenai Peninsula. Our microsatellite analysis showed that 72% of the sampled individuals had white spruce ancestry, while 14% had Sitka spruce ancestry; some individuals classified as white spruce had Sitka spruce plastid genotypes. Our data suggest that white spruce was the ancestral seed parent, and Sitka spruce alleles originated from pollen. Hybridization played a crucial role in allowing Sitka spruce to expand its range in response to climate change.