Abstract
BackgroundEntering and exiting winter dormancy present important trade-offs between growth and survival at northern latitudes. Many forest trees display local adaptation across latitude in traits associated with these phenology transitions. Transfers of a species outside its native range introduce the species to novel combinations of environmental conditions potentially requiring different combinations of alleles to optimize growth and survival. In this study, we performed genome wide association analyses and a selection scan in a P. trichocarpa mapping population derived from crossings between clones collected across the native range and introduced into Sweden. GWAS analyses were performed using phenotypic data collected across two field seasons and in a controlled phytotron experiment.ResultsWe uncovered 584 putative candidate genes associated with spring and autumn phenology traits as well as with growth. Many regions harboring variation significantly associated with the initiation of leaf shed and leaf autumn coloring appeared to have been evolving under positive selection in the native environments of P. trichocarpa. A comparison between the candidate genes identified with results from earlier GWAS analyses performed in the native environment found a smaller overlap for spring phenology traits than for autumn phenology traits, aligning well with earlier observations that spring phenology transitions have a more complex genetic basis than autumn phenology transitions.ConclusionsIn a small and structured introduced population of P. trichocarpa, we find complex genetic architectures underlying all phenology and growth traits, and identify multiple putative candidate genes despite the limitations of the study population.
Highlights
Entering and exiting winter dormancy present important trade-offs between growth and survival at northern latitudes
The study presented here is the first to study the genetic basis of phenology traits in a population of P. trichocarpa introduced to northern Europe
We find considerable and heritable phenotypic variation in and complex genetic architectures underlying most of the studied phenology and growth traits, and identify multiple putative candidate genes despite the small and structured study population
Summary
Entering and exiting winter dormancy present important trade-offs between growth and survival at northern latitudes. We performed genome wide association analyses and a selection scan in a P. trichocarpa mapping population derived from crossings between clones collected across the native range and introduced into Sweden. Populations of widespread species often display signatures of phenotypic and genetic adaptation to their native environments, even in species with considerable gene flow between the populations [6]. This phenomenon, known as local adaptation, often arises from positive selection [7], which leaves distinct and detectable signatures across the genome [8, 9]. Due to the polygenic nature of these traits, the genetic architecture of local adaptation to climate can be very diverse among even closely related species, despite the adaptation being driven by very similar environmental conditions (e.g. [15, 16])
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