Fehrer Judith, Nagy Nejedlá Michaela, Hellquist C Barre, Bobrov Alexander A, Kaplan Zdenek
Institute of Botany, Czech Academy of Sciences, Průhonice, Czechia.
Department of Biology, Massachusetts College of Liberal Arts, North Adams, MA, United States.
Front Plant Sci. 2022 Nov 3;13:1042517. doi: 10.3389/fpls.2022.1042517. eCollection 2022.
Aquatic plant species are often widespread, even across continents. They pose a challenge to species delimitation and taxonomy due to their reduced morphology and high phenotypic plasticity. These difficulties are even more pronounced in the case of interspecific hybridization. We investigate the aquatic plant genus for the first time on a worldwide scale. Expert species determination is aided by sequencing of nuclear ribosomal and regions and the plastid intergenic spacers and . Nuclear markers are used to infer hybridization, and the maternal origin of hybrids is addressed with plastid markers. Pure species are subjected to phylogenetic analyses. Two main lineages are found: one consists of , , , and , the other includes and The widespread species , , and show intraspecific genetic variation, which is structured geographically. Many intraspecific hybrids, which are usually fertile, occur between those genotypes. Interspecific hybrids, which are consistently sterile, are detected among all widespread species; some are reported for the first time in several countries and regions. They originated multiple times from reciprocal crosses and reflect the geographical origins of parental genotypes. Intraspecific genetic variation can be higher than interspecific differences between closely related species. Comparison of phenotypic variation in the field and in cultivation with genotypic variation shows that numerous conspicuous forms have been overestimated taxonomically. These are resolved as phenotypes responding to unusual environments, have recurrently evolved adaptations, or represent extreme forms of continuous variation of the recognized species. However, some specific regional lineages, which have evolved from variable species, may be interpreted as early steps of the speciation process. Hybridization has been underestimated in some regions as a source of diversity, and the respective hybrid plants have been misidentified as intraspecific taxa or even as separate species. Many erroneous entries in sequence databases are detected and summarized. This work provides a sound basis for species delimitation and hybrid recognition in this difficult genus.
水生植物物种通常分布广泛，甚至跨越各大洲。由于其形态简化和高表型可塑性，它们给物种界定和分类学带来了挑战。在种间杂交的情况下，这些困难更为明显。我们首次在全球范围内对该水生植物属进行研究。通过对核糖体 和 区域以及质体基因间隔区 和 的测序辅助专家进行物种鉴定。核标记用于推断杂交情况，质体标记用于确定杂交种的母本来源。对纯合物种进行系统发育分析。发现了两个主要的谱系：一个由 、 、 、 和 组成，另一个包括 和 。广泛分布的物种 、 和 表现出种内遗传变异，且这种变异具有地理结构。在这些基因型之间出现了许多通常可育的种内杂交种。在所有广泛分布的物种中均检测到种间杂交种，且这些杂交种始终不育；在一些国家和地区首次报道了其中一些杂交种。它们多次起源于正反交，并反映了亲本基因型的地理来源。种内遗传变异可能高于近缘物种之间的种间差异。将田间和栽培条件下的表型变异与基因型变异进行比较表明，许多显著的形态在分类学上被高估了。这些形态被解析为对异常环境做出反应的表型，反复进化出适应性，或代表已识别物种连续变异的极端形式。然而，一些从可变物种进化而来的特定区域谱系可能被解释为物种形成过程的早期步骤。在一些地区，杂交作为多样性的一个来源被低估了，相应的杂交植物被错误地鉴定为种内分类群甚至单独的物种。检测并总结了序列数据库中的许多错误条目。这项工作为这个困难属的物种界定和杂交种识别提供了坚实的基础。
