Hybrid zone Exome capture

Although interspecific hybridization may reduce fitness, it can also promote rapid adaptation to novel environments. A genomic region acquired from Pinus parviflora inhabiting higher temperatures could increase the fitness of a recipient alpine species Pinus pumila adapted to lower temperatures, particularly in the context of global warming. However, the large genome size of Pinus species has made the genome wide studies impractical. Therefore, we applied exome capture and investigated the genome-wide hybridization patterns of P. pumila and P. parviflora in the Hakkoda Mountains, Japan. Hybrid individuals occurred predominantly at mid-elevations and possessed P. pumila-like chloroplasts, suggesting that P. pumila is the most recent pollen parent. Genome-wide patterns of introgression indicated that more frequent backcrossing with P. pumila and limited backcrossing with P. parviflora. These patterns may result from geographic isolation, phenological differences in flowering time, and natural selection favoring hybrids in specific environmental contexts. Specifically, in terms of natural selection, tall hybrids may be advantageous for light competition at mid-elevations compared to the surrounding moorland vegetation, while smaller, pure P. pumila individuals may be favored in the high-altitude wind-exposed alpine fellfields, and hybrids with reduced height compared to those of pure P. parviflora may be disadvantaged in low-elevation broadleaved deciduous forests. Future functional analysis of introgressed genes could elucidate the adaptive significance of these hybridization patterns along elevational and environmental gradients.

尽管种间杂交可能降低适合度，却也可推动物种快速适应全新环境。栖息于高温环境的日本五针松（Pinus parviflora）所携带的基因组片段，可提升适应低温的高山物种偃松（Pinus pumila）的适合度，在全球变暖的背景下这一效应尤为显著。然而，松属植物庞大的基因组规模使得全基因组研究难以开展。因此，本研究采用外显子组捕获（exome capture）技术，对日本八甲田山区的偃松与日本五针松的全基因组杂交模式展开了探究。杂交个体主要分布于中海拔区域，且携带与偃松相似的叶绿体，这表明偃松是更近的花粉供体亲本。全基因组渐渗模式显示，杂交个体与偃松的回交更为频繁，而与日本五针松的回交则相对有限。这类杂交模式可能由地理隔离、开花物候差异，以及特定环境下自然选择对杂交个体的青睐所导致。具体而言，从自然选择角度来看，相较于周边的泥炭地植被，中海拔区域的高大杂交个体在光照竞争中更具优势；而在高海拔受风蚀的高山碎石坡中，体型更小的纯种偃松个体更受选择青睐；而相较于纯种日本五针松个体的矮化杂交个体，则在低海拔阔叶落叶林中处于竞争劣势。未来对渐渗基因的功能分析，有望阐明这些杂交模式沿海拔梯度与环境梯度的适应性意义。