From common gardens to candidate genes: Exploring local adaptation to climate in red spruce

Local adaptation to climate is common in plant species and has been
studied in a range of contexts, from improving crop yields to predicting
population maladaptation to future conditions. The genomic era has brought
new tools to study this process, which was historically explored through
common garden experiments.  In this study, we combine genomic
methods and common gardens to investigate local adaptation in red spruce
and identify environmental gradients and loci involved in climate
adaptation. We first use climate transfer functions to estimate the impact
of climate change on seedling performance in three common gardens. We then
explore the use of multivariate gene-environment association (GEA) methods
to identify genes underlying climate adaptation, with particular attention
to the implications of conducting genome scans with and without correction
for neutral population structure. This integrative approach uncovered
phenotypic evidence of local adaptation to climate and identified a set of
putatively adaptive genes, some of which are involved in three main
adaptive pathways found in other temperate and boreal coniferous species:
drought tolerance, cold hardiness, and phenology. These putatively
adaptive genes segregated into two “modules” associated with different
environmental gradients. This study nicely exemplifies the multivariate
dimension of adaptation to climate in trees.