PRJNA824947
History and environment shape spatial genetic variation and predict climate maladaptation in a narrowly distributed serotinous pine, Pinus muricata.
Understanding the distribution of genetic diversity and differentiation in species with disjunct and isolated populations is critical for assessing how environment shapes genetic variation and the potential response to climate change. In contrast to the large distributions and population sizes of most pine species, Pinus muricata (Bishop pine) occurs in a small number of isolated and disjunct populations occupying a narrow band of environmental conditions along the coast of western North America. We used genotyping by sequencing to generate population genomic data for trees sampled from nearly all existing populations of P. muricata (213 individuals, 7,828 loci) to describe the spatial arrangement of genetic differentiation and diversity. We used genetic-environment association (GEA) analyses to quantify the contribution of environmental variables to local adaptation and spatial genetic structure. Based on these results, we quantified relative levels of potential maladaptation given future climate projections at time intervals 2041 - 2060 and 2081 - 2100. Our analyses reveal pronounced spatial genetic structure across the distribution, with most populations forming genetically identifiable groups across a latitudinal gradient, and remarkable evidence for differentiation among three proximally distributed stands on Santa Cruz Island. Despite occurring in small, isolated populations, P. muricata populations do not exhibit strongly reduced diversity. GEA analyses suggested that specific soil and climate variables have contributed to local adaptation. Genomic offset analyses suggest geographic variation in potential maladaptation, with northern populations experiencing higher levels under projected climate change. Overall, our results suggest that isolation and local adaptation have shaped genetic variation among disjunct populations, and illustrate the consequences of this variation for P. muricata under projected climate change.