Climate-driven local adaptation of ecophysiology and phenology in balsam poplar, Populus balsamifera L.

Premise of the study : During past episodes of climate change, many plant species experienced large-scale range expansions. Expanding populations likely encountered strong selection as they colonized new environments. In this study we examine the extent to which populations of the widespread forest tree Populus balsamifera L. have become locally adapted as the species expanded into its current range since the last glaciation. Methods : We tested for adaptive variation in 13 ecophysiology and phenology traits on clonally propagated genotypes originating from a range-wide sample of 20 subpopulations. The hypothesis of local adaption was tested by comparing among-population variation at ecologically important traits (Q(ST)) to expected variation based on demographic history (F-ST) estimated from a large set of nuclear single nucleotide polymorphism loci. Key results : Evidence for divergence in excess of neutral expectations was present for eight of 13 traits. Bud phenology, petiole