Genetic and Phenotypic Variation
Our dataset of 192 genotypes analyzed with ddRAD yielded 9195 SNP loci. The 16 Arizona populations show strong differentiation with an average pairwise FST = 0.175 and 95% confidence interval of 0.144-0.205. Consistent with our first hypothesis, we found significant within and among population variation for traits at each of the three common gardens (Table 1, Fig. 3), with phenology traits exhibiting higher differentiation at the population than the genotype level in all but one case. For SLA, height, and diameter at root crown (DRC), the relative contribution of population vs. genotype varied among gardens. Traits measured in the hottest common garden (Yuma) exhibited stronger population than genotype effects in four out of the five traits; for SLA, the proportion of variance explained by genotype was higher than the proportion explained by population, although it was very close (27% vs. 24%, respectively; Table 1). This garden thus produced higher values of QST (the proportion of the genetic variance that is found among rather than within populations, see next section).
Phenotypic plasticity across the three gardens showed significant population differences in all traits except SLA (Table 1, Fig. 3). Here, the lower sample size of seven populations with no populations from the hottest locations may have contributed to this non-significant effect. Population explained more variance in plasticity in the growth traits compared to the phenology traits (Table 1).