Data from: Genomic and phenotypic architecture of a spruce hybrid zone (Picea sitchensis x P. glauca)

Interspecific hybridization may enhance the capacity of populations to adapt to changing environments, and has practical implications for reforestation. We use genomewide estimates of admixture and phenotypic traits for trees in a common garden to examine the extent and direction of gene flow across a Picea hybrid zone, testing assumptions of the bounded hybrid superiority and tension zone models of hybrid zone maintenance. Seeds were collected from the ecological transition zone spanning from maritime to continental climates across the Picea sitchensis-P. glauca contact zone, and 721 trees were planted in a common garden experiment within the hybrid zone. Individuals were genotyped using a panel of 384 candidate-gene single nucleotide polymorphisms (SNPs) putatively associated with adaptive traits in Picea, and phenotyped at age ten for height and autumn cold hardiness. Low interspecific heterozygosity in hybrids indicated intrinsic reproductive barriers were too weak to prevent widespread recombination, although introgression appeared asymmetric with P. sitchensis dominating the zone. While marker-based hybrid index was strongly correlated with climate and geography, phenotypic traits exhibited weak or no significant clines. Our results indicated that exogenous selection appeared to play a strong role in the distribution and structure of this hybrid zone, indicative of an environmentally determined bounded hybrid superiority model of hybrid zone maintenance, although endogenous mechanisms could not be ruled out. This study provides insight into the mechanisms underlying adaptation across ecologically transitional hybrid zones that will ultimately provide an additional tool in managing these economically important tree species.

种间杂交可增强种群适应多变环境的能力，对再造林实践具有重要现实意义。本研究以云杉属（Picea）杂交带的树木为研究对象，利用同质园实验（common garden）中植株的全基因组混合组分估计结果与表型性状，探究该杂交带的基因流范围与方向，检验有界杂种优势模型（bounded hybrid superiority）与张力区模型（tension zone model）这两类杂交带维持假说的前提假设。研究人员从横跨西加云杉（Picea sitchensis）与白云杉（P. glauca）分布接触带、涵盖海洋性至大陆性气候的生态过渡区采集种子，将培育出的721株幼苗定植于该杂交带内的同质园实验场地。研究团队采用包含384个候选基因的单核苷酸多态性（single nucleotide polymorphism, SNP）标记面板对个体进行基因分型，此类标记被推测与云杉属植物的适应性性状相关；同时对10年生个体的树高与秋季抗寒性开展表型测定。杂种个体较低的种间杂合度表明，内在生殖屏障强度不足，无法阻止广泛的基因重组，但渐渗现象呈现不对称特征，西加云杉在该杂交带中占据主导地位。基于分子标记的杂种指数与气候、地理因素显著相关，而表型性状仅表现出微弱或无显著的渐变群分布特征。研究结果显示，外源选择（exogenous selection）在该杂交带的分布与结构维持中发挥了关键作用，表明该杂交带的维持符合环境决定的有界杂种优势模型，不过内源选择（endogenous selection）机制也无法被完全排除。本研究揭示了生态过渡型杂交带的适应机制，最终可为这类具有重要经济价值的树木物种的管理提供新的辅助工具。