Genetic diversity and seed production in Santa Lucia fir (Abies bracteata), a relict of the Miocene Broadleaved Evergreen Forest

Abstract

Santa Lucia fir (Abies bracteata), is a unique fir, the sole member of the subgenus Pseudotorreya. It is a relict of the Miocene broadleaved evergreen sclerophyll forest, and is now restricted to a highly fragmented range in the Santa Lucia Mountains of central coastal California. Expected heterozygosity for 30 isozyme loci in 18 enzyme systems, averaged over six populations that spanned the species’ north–south range, was only 0.036. Despite a fragmented range and isolated populations, differentiation (F ST) was only 0.080 for mature trees, and the number of migrants per generation (Nm) was 2.88 or 3.83, depending on the method of estimation. F ST for embryos was lower, 0.025, and Nm correspondingly higher, 9.75. Nei’s genetic distances were small and unrelated to geographic distances between populations. The proportion of full seeds per cone was only 0.082–0.488, depending on population, which suggests a high incidence of selfing followed by embryo abortion. However, the level of accumulated inbreeding, F IS, in mature trees was low, only 0.049. By contrast, F IS for embryos was 0.388, which indicates a high proportion of selfed progeny, in agreement with the low seed yields. The difference in inbreeding coefficients between seed trees and their progeny suggest that most inbreds are eliminated before maturity and, therefore, seed production, already low, overestimates the true potential for regeneration of these populations. These results have implications for conservation.