Subalpine fir microsatellite variation reveals the complex relationship between var. lasiocarpa and var. bifolia

Abstract

Subalpine fir, Abies lasiocarpa, occurs throughout western North America, often in forest–tundra parkland. To resolve the presence of varieties in this species, we surveyed microsatellite genetic markers in 11 populations containing three putative varieties of Abies lasiocarpa: (1) var. lasiocarpa, (2) var. bifolia, and (3) var. arizonica. We tested primers from related taxa, and 13 of the best primer pairs were used for assays. Within populations, both heterozygosity and allelic richness were approximately 10% lower in var. lasiocarpa. The STRUCTURE procedure struggled to assign populations to groups correctly; at K = 3, individuals were assigned to their putative varieties with approximately 70% accuracy. Regardless, both lasiocarpa and bifolia were correctly assigned more than expected by chance, indicating that these taxa are distinct. A dendrogram of genetic distances showed var. arizonica to exhibit higher evolutionary distance from the other two varieties and serves as an outgroup. The dendrogram also showed a nesting of var. bifolia clades within var. lasiocarpa, indicating a complex relationship between var. lasiocarpa and var. bifolia. Comparisons among the STRUCTURE population assignments for K = 2, K = 3, and K = 4 identified populations with cryptic admixture and indicate a “ lasiocarpa–bifolia” subspecies complex that warrants further study.