Local adaptation at fine spatial scales: an example from sugar pine (Pinus lambertiana, Pinaceae)

The forest environment can be heterogeneous over short physical distances, so that local adaptation by conifers, especially when selection is strong or gene flow restricted, may occur at fine spatial scales. Here, we examine patterns of genetic diversity across ten sugar pine (Pinus lambertiana Dougl.) populations located within the Lake Tahoe Basin of California and Nevada, USA. This region covers an area of only 1300 km(2) but is heterogeneous with respect to local environmental conditions. We associated 475 single nucleotide polymorphisms (SNPs) with five phenotypic traits, as well as with 11 environmental variables that describe the maternal tree environments. Phenotypes were measured in a common garden established from offspring of 108 maternal trees sampled from eight populations. Genetic, phenotypic, and environmental variation was pronounced among populations. Association genetic analysis identified six associations between SNPs and phenotypic traits, as well as 31 associations between SNPs and environmental principal components (PCs). Only two SNPs were shared among these sets of results. One of these two SNPs was associated with carbon isotope ratios that were correlated to an environmental PC representing soil and climate variables involved with water availability. Utilization of this three-pronged approach established conceptual links between genotypes and phenotypes in an ecological context.