School of Life Science, Luoyang Normal University, 6 Jiqing Road, 471934, Luoyang, P. R. China.
Regional nature park of the Trient Valley, La Place 24, 1922, Salvan, Switzerland.
BMC Plant Biol. 2022 Oct 28;22(1):504. doi: 10.1186/s12870-022-03879-0.
Mountains of the world host a significant portion of all terrestrial biodiversity, and the region of the Qinghai-Tibet Plateau (QTP) stands as one of the most remarkable mountain regions on Earth. Because many explosive radiations occurred there, the QTP is a natural laboratory which is ideal to investigate patterns and processes linked to speciation and diversification. Indeed, understanding how closely related and sympatric species diverged is vital to explore drivers fostering speciation, a topic only rarely investigated in the QTP. By combining genomic and environmental data, we explored the speciation process among three closely related and sympatric species, Gentiana hexaphylla, G. lawrencei and G. veitchiorum in the QTP region.
Combining genome sizes and cytological data, our results showed that G. hexaphylla and G. veitchiorum are diploid, whereas G. lawrencei is tetraploid. Genetic clustering and phylogenetic reconstruction based on genomic SNPs indicated a clear divergence among the three species. Bayesian clustering, migrant, and D-statistic analyses all showed an obvious signature of hybridization among the three species, in particular between G. lawrencei and both G. hexaphylla and G. veitchiorum in almost all populations. Environmental variables related to precipitation and particularly temperature showed significant differences among the three gentians, and in fact a redundancy analysis confirmed that temperature and precipitation were the major climatic factors explaining the genetic differentiation among the three species.
Our study suggested that ancient hybridization, polyploidization, geological isolation and the evolution of different climatic preferences were all likely to be involved in the divergence of the three Gentiana species, as may be the case for many other taxa in the QTP region.
世界上的山脉承载了地球上大量的生物多样性，而青藏高原地区（QTP）则是地球上最显著的山脉之一。由于那里发生了许多爆发性辐射，QTP 是一个理想的自然实验室，可用于研究与物种形成和多样化相关的模式和过程。事实上，了解密切相关和同域的物种是如何分化的，对于探索促进物种形成的驱动因素至关重要，而这在 QTP 地区很少被研究。通过结合基因组和环境数据，我们探索了 QTP 地区三种密切相关和同域的物种，即六叶龙胆、劳伦斯龙胆和威氏龙胆的物种形成过程。
结合基因组大小和细胞学数据，我们的结果表明，六叶龙胆和威氏龙胆是二倍体，而劳伦斯龙胆是四倍体。基于基因组 SNPs 的遗传聚类和系统发育重建表明，这三个物种之间存在明显的分化。贝叶斯聚类、移民和 D 统计分析都表明，这三个物种之间存在明显的杂交迹象，特别是在劳伦斯龙胆和六叶龙胆和威氏龙胆的几乎所有种群中。与降水有关的环境变量，特别是温度，在这三种龙胆中存在显著差异，实际上，冗余分析证实温度和降水是解释这三个物种遗传分化的主要气候因素。
我们的研究表明，古老的杂交、多倍体化、地质隔离以及不同气候偏好的进化都可能参与了这三个龙胆物种的分化，就像 QTP 地区的许多其他分类群一样。
