Genetic structure of yellow cedar (Chamaecyparis nootkatensis)

Abstract

A range-wide survey of isozyme variation in yellow cedar (Chamaecyparis nootkatensis (D. Don) Spach; or Alaska cedar) found significant inbreeding and a striking geographical structure. The proportion of diversity among populations (GST) was 0.139, and three major geographical groups were evident: (1) Vancouver Island - mid-north coast British Columbia (B.C.); (2) south coast B.C. - Washington state; (3) southeast Alaska. This may indicate the presence of multiple refugia during ice-age range contractions. Geographically disjunct populations in Oregon and southeastern B.C. were also genetically distinct. Adult inbreeding coefficients (F) were usually positive but varied widely among populations, as did gene diversity. The overall average of F = 0.18 suggests that considerable selfing (ca. 30%) occurs in this species. Other statistics were more typical for a conifer: within population heterozygosity (HS) averaged 0.148, total gene diversity (HT) was 0.171, and the number of alleles per locus and percentage polymorphic loci averaged 1.68 and 50, respectively. This geographic structure has implications for species conservation and for breeding programs. Also, previous studies of other Cupressoideae (Rich. ex Sweet) species indicate that these levels of inbreeding and population structure are not uncommon, and may influence evolutionary divergence in the Cupressoideae.Key words: Chamaecyparis nootkatensis, yellow cedar, genetic structure, inbreeding, phylogeography, isozymes.