Adaptive variants are independently sorted
Across the species geographic distribution, climatic heterogeneity explains significant genomic variation. In particular, TSEAS and PWQ showed strong associations between environments and gene pools. The patterns of genomic turnover associated with the studied climatic variables are aligned with the climatic gradients of the region (Figure 5). These associations are indicative of the multidimensional patterns of adaptation resulting in orthogonal intraspecific selection among SNPs (White & Butlin, 2021). Here, we define dimensionality as the interaction between orthogonal climate variables to independently describe each habitat. Our dimensionality is driven by climate, and the independent sorting of putatively adaptive variants is indicative of this complex pattern. It has been modelled that local adaptation increases with dimensionality (MacPherson et al. 2015), and it likely leads to dimensionality of phenotypic traits (Kirkpatrick and Meyer 2004; McGuigan et al. 2005). Indeed, there is evidence of intraspecific variation among growth and morphological traits (e.g., height and diameter at breast height) locally adapted in jarrah, associated to climatic factors (O’Brien et al., 2007, 2010; Koch & Samsa, 2007).
In some ways, increased dimensionality is ubiquitous with increased habitat heterogeneity, and habitat heterogeneity has been shown to drive signatures of adaptation to temperature and precipitation in tree species (Shryock et al. 2020; von Takach et al., 2021; Walters et al., 2021). While these studies did not explore dimensionality explicitly, their results nevertheless show that tree species are able to independently adapt to multiple types of environments. While such patterns of differential adaptation makes management of the species more complex and nuanced in the future, our results provide a level of understanding that will allow for targeted responses to changing climatic conditions in different areas.