Exome Sequencing and Allele Dosage Analysis of Coast Redwood, a Hexaploid Conifer, Identifies a Major Population Break South of San Francisco Bay

Abstract

1The coast redwood (Sequoia sempervirens) is a long-lived, hexaploid conifer of high ecological, cultural, and economic value whose range has been greatly reduced by historical logging [1]. Effective restoration and conservation depend on understanding patterns of genetic differentiation across the redwood range to delineate populations for management prioritization. Yet, past range-wide studies provided only a partial picture of population structure in coast redwood as they relied on a limited set of genetic markers [2, 3] or limited sampling, as sequencing was done on the same range-wide provenance collection [4, 5]. Here, we analyze 334,029 SNPs from a new range-wide set of 224 individuals using a dosage-based approach that accounts for polyploidy. Principal coordinates and clustering analyses reveal clear latitudinal structure, with a steeper break south of San Francisco Bay. Outlier SNP analysis identified new candidate loci involved in salinity tolerance, climate stress response, and nutrient uptake, suggesting potential local adaptation. These results point to the central role of geography in shaping genetic variation in coast redwood and give scientific basis for designing new conservation and management strategies aimed at preserving the species genetic diversity into the future.