Species differentiation in the genus <i>Chara</i> (Charophyceae): considerable phenotypic plasticity occurs within homogenous genetic groups

Charophytes are benthic algae with a complex morphology and high phenotypic plasticity. This has led to ambiguities in species delineation. However, until now genetic studies on <i>Chara</i> have been based on samples collected from a restricted geographic range or only included a restricted number of taxa. This may have hindered a general interpretation of the results. We applied barcoding of <i>matK</i>, a rapidly evolving coding section of the plastid genome, in 324 <i>Chara</i> samples collected from 19 countries, in order to test whether the distribution of barcode haplotypes among individuals was consistent with species boundaries as they are currently understood. The phylogenetic tree grouped the 324 <i>Chara</i> individuals, which according to commonly used identification keys represented 29 species, into 12 well-defined groups (i.e. monophyletic morphospecies or groups of morphospecies). Considerable morphological variation occurred within genetically homogeneous groups. This included traits which are commonly used for <i>Chara</i> species determination, such as the length and number of spine cells, the length of stipulodes and bract cells, cortication (tylacanthous, isostichous, aulacanthous and absent cortication), as well as sex differentiation. However, there were also substantial genetic differences among morphologically similar species (e.g. <i>C. virgata</i> – <i>C. globularis – C. connivens</i>). No morphological trait consistently reflected genetic differences. This indicates that morphological traits for specific taxa may serve as diagnostic tools for species delimitation, but that they are not generally suitable for inferring genetic differentiation or phylogenetic relationships. We propose that (i) <i>C. virgata</i> and <i>C. strigosa</i>, (ii) <i>C. liljebladii, C. horrida</i> and <i>C. baltica</i>, and (iii) <i>C. hispida, C. rudis</i> and <i>C. polyacantha</i> are conspecific. Our data also indicate that <i>C. gymnophylla</i> should be divided into tylacanthous forms (which are closely related to <i>C. contraria</i>) and aulacanthous forms (which are related to <i>C. vulgaris</i>).轮藻（Charophytes）是一类形态复杂且表型可塑性（phenotypic plasticity）极高的底栖藻类，这使得其物种界定（species delineation）存在诸多歧义。然而，迄今为止针对轮藻属（Chara）的遗传学研究均基于有限地理区域采集的样本，或仅纳入了少量类群，这可能阻碍了对研究结果的一般性解读。本研究对采自19个国家的324份轮藻属样本开展了matK基因的DNA条形码（barcoding）分析，该基因是质体基因组（plastid genome）中快速进化的编码区段，以此检验条形码单倍型（haplotype）在个体间的分布是否与当前认知的物种边界相符。系统发育树（phylogenetic tree）将根据常用分类鉴定手册归为29个物种的324份轮藻属个体划分为12个界定清晰的类群（即单系（monophyletic）形态种（morphospecies）或形态种类群）。在遗传同质类群内部存在显著的形态变异，其中包括常用于轮藻属物种鉴定的性状：如刺细胞的长度与数量、托叶及苞片细胞的长度、皮层类型（具棘皮层（tylacanthous）、等列皮层（isostichous）、沟纹皮层（aulacanthous）及无皮层），以及性别分化特征。然而，形态相似的物种间也存在显著的遗传差异（如C. virgata、C. globularis与C. connivens）。未发现任何形态性状能够稳定反映遗传分化（genetic differentiation），这表明针对特定类群的形态性状或许可作为物种界定的鉴定工具，但通常并不适用于推断遗传分化或系统发育关系（phylogenetic relationships）。本研究提出以下类群应归为同种：（i）C. virgata与C. strigosa；（ii）C. liljebladii、C. horrida与C. baltica；以及（iii）C. hispida、C. rudis与C. polyacantha。本研究数据还表明，C. gymnophylla应被划分为两类：与C. contraria近缘的具棘皮层类群，以及与C. vulgaris近缘的沟纹皮层类群。

搜集汇总

背景与挑战

背景概述

该数据集基于一项针对轮藻属（Chara）的遗传学研究，使用matK基因条形码技术分析了来自全球19个国家的324个样本，旨在验证物种边界。研究发现，形态学分类下的29个物种在遗传上被归为12个组，揭示了在遗传同质组内存在显著的形态可塑性，包括常用于物种鉴定的特征变异，同时形态相似物种间有遗传差异，表明形态特征不能作为推断遗传分化的可靠指标，并提出了部分物种可能为同种的见解。