Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Yokohama, Kanagawa, Japan.
Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Nagasaki, Japan.
Mol Ecol. 2023 Jun;32(11):2945-2963. doi: 10.1111/mec.16908. Epub 2023 Mar 15.
A compelling interest in marine biology is to elucidate how species boundaries between sympatric free-spawning marine invertebrates such as bivalve molluscs are maintained in the face of potential hybridization. Hybrid zones provide the natural resources for us to study the underlying genetic mechanisms of reproductive isolation between hybridizing species. Against this backdrop, we examined the occurrence of introgressive hybridization (introgression) between two bivalves distributed in the western Pacific margin, Atrina japonica and Atrina lischkeana, based on single-nucleotide polymorphisms (SNPs) derived from restriction site-associated DNA sequencing. Using 1066 ancestry-informative SNP sites, we also investigated the extent of introgression within the genome to search for SNP sites with reduced interspecies gene flow. A series of our individual-level clustering analyses including the principal component analysis, Bayesian model-based clustering, and triangle plotting based on ancestry-heterozygosity relationships for an admixed population sample from the Seto Inland Sea (Japan) consistently suggested the presence of specimens with varying degrees of genomic admixture, thereby implying that the two species are not completely isolated. The Bayesian genomic cline analysis identified 10 SNP sites with reduced introgression, each of which was located within a genic region or an intergenic region physically close to a functional gene. No, or very few, heterozygotes were observed at these sites in the hybrid zone, suggesting that selection acts against heterozygotes. Accordingly, we raised the possibility that the SNP sites are within genomic regions that are incompatible between the two species. Our finding of restricted interspecies gene flow at certain genomic regions gives new insight into the maintenance of species boundaries in hybridizing broadcast-spawning molluscs.
对海洋生物学的强烈兴趣在于阐明在潜在杂交的情况下，例如双壳类软体动物等自由产卵的海洋无脊椎动物之间的种间边界是如何维持的。杂交区为我们提供了研究杂交物种之间生殖隔离的潜在遗传机制的自然资源。在此背景下，我们基于来自限制位点相关 DNA 测序的单核苷酸多态性 (SNP)，检查了分布在西太平洋边缘的两种双壳类动物，日本鲍和李氏鲍之间的渗入杂交（基因渐渗）的发生情况。使用 1066 个具有祖先信息的 SNP 位点，我们还研究了基因组内基因渐渗的程度，以寻找具有降低种间基因流的 SNP 位点。我们对个体水平聚类分析的一系列研究，包括主成分分析、贝叶斯模型聚类分析和基于混合种群样本（来自日本濑户内海）的祖先杂合性关系的三角形绘图，一致表明存在具有不同程度基因组混合的标本，从而表明这两个物种并非完全隔离。贝叶斯基因组渐变分析确定了 10 个具有降低基因渐渗的 SNP 位点，每个位点都位于基因区域内或基因间区域内，与功能基因物理上接近。在杂交区，这些位点几乎没有或很少观察到杂合子，这表明选择不利于杂合子。因此，我们提出了这样的可能性，即 SNP 位点位于两个物种之间不兼容的基因组区域内。我们在某些基因组区域发现的有限的种间基因流为杂交浮游贝类物种边界的维持提供了新的见解。
