The role of intraspecific competition during post-glacial recolonization: a Norway spruce case study

During the climate warming after the last glaciation event, many plant species underwent an expansion that still today shapes their current distribution and population structure. Norway spruce was no exception, and its current distribution is the result of a complex demographic history. Recolonization abilities depend on the competitive ability, but little is known about the shaping force of competition during post-glacial expansions in tree species. In the present study, we investigated the different competitive abilities of the post-glacial genetic clusters of Norway spruce. We assessed the adaptations underlying the trunk diameter, wood density and tracheid traits using a large dataset of 4,461 individuals from 396 half-sib families, 118,145 SNPs from, mixed linear models and multiple Genome-Wide Association Studies, in the progeny tests implemented by the Swedish breeding program. We show that (i) in terms of competition, macroscopic traits are what matters, much more so than tracheid dimensions; (ii) the ability to benefit from early competition is stronger in core populations or ancient refugia; and (iii) population structure for Norway spruce is intrinsically associated with latitude, and as such is a good predictor of adaptation but an impediment for detecting underlying genetic variants. ### Competing Interest Statement The authors have declared no competing interest.