Genomic and phenotypic adaptation tunes an endangered California plant to the fog that climate change and wind energy will reshape

Mediterranean-climate regions support some of the most diverse and endemic-rich plant communities in the world, yet the genomic basis of plant adaptation to coastal fog, which buffers dry-season water stress in at least some of these systems, remains almost entirely uncharacterized. We investigated the population genomics of the endangered Gaviota tarplant (Deinandra increscens subsp. villosa), endemic to the fog-swept central California coastline, where a wind farm has recently been built across the largest remaining population. Using whole-genome resequencing across the fragmented range of the subspecies, we found a non-directional association between wind connectivity and genetic similarity, suggesting that the wind farm could affect gene flow among plant stands. Genome-wide association analyses identified polygenic local adaptation to fog, with GO enrichment analyses converging on the importance of cell wall remodelling, osmoregulation, developmental timing, light perception, and immunity. Herbarium specimens spanning a century reveal broader architecture and fewer disk florets in foggier, wetter sites, traits that may be underpinned by candidate genes we uncovered. Of 31 fog-associated genomic peaks, only a centromere-associated haplotype showed one of the strongest spatial associations with long-term fog and uniquely tracked germination-year fog, suggestive of early-season environmental filtering. A year of extreme drought and unusually rich fog yielded two further signals consistent with this: increased long runs of homozygosity and a smoother landscape-level allele-frequency surface. This baseline identifies candidate climate-resilient genotypes for active management and motivates experimental trials to test early-season filtering of fog-adaptive genotypes.