Data from: DNA variation in the phenotypically-diverse brown alga Saccharina japonica

BACKGROUND: Saccharina japonica (Areschoug) Lane, Mayes, Druehl et Saunders is an economically important and highly morphologically variable brown alga inhabiting the northwest Pacific region. On the basis of nuclear (ITS), plastid (rbcLS) and mitochondrial (COI) DNA sequence data, we have analyzed the genetic composition of typical Saccharina japonica (TYP) and its two common morphological varieties, known as the “longipes” (LON) and “shallow-water” (SHA) forms seeking to clarify their taxonomical status and to evaluate the possibility of cryptic species within S. japonica. RESULTS: The data show that the TYP and LON forms are very similar genetically in spite of drastic differences in morphology, life history traits, and ecological preferences. Both, however, are genetically quite different from the SHA form. The two Saccharina lineages are distinguished by 109 fixed single nucleotide differences as well as by seven fixed length polymorphisms (based on a 4,286 bp concatenated dataset that includes three gene regions). The GenBank database reveals a close affinity of the TYP and LON forms to S. japonica and the SHA form to S. cichorioides. The three gene markers used in the present work have different sensitivity for the algae species identification. The COI gene is the most discriminant gene marker. However, the 5’-COI “barcoding” region (~ 650 bp) is not satisfactory and even misleading for identification purposes, at least in the case of algae species that might have experienced historical hybridization events. CONCLUSION: Taking into account the potential roles of phenotypic plasticity in evolution, we conclude that the TYP and LON forms represent examples of algae phenotypic diversification that enables successful adaptation to contrasting shallow- and deep-water marine environments, while the SHA form is very similar to S. cichorioides and should be considered a different species. Practical applications for algal management and conservation are shortly considered.

背景：日本海带（Saccharina japonica，(Areschoug) Lane, Mayes, Druehl et Saunders）是栖息于西北太平洋海域的具有重要经济价值的褐藻，其形态变异度极高。本研究基于细胞核（ITS）、质体（rbcLS）及线粒体（COI）的DNA序列数据，对典型日本海带（TYP）及其两种常见形态变种——“长柄型”（LON）与“浅海型”（SHA）的遗传组成展开分析，旨在明确它们的分类学地位，并探究日本海带类群内存在隐存种的可能性。
结果：数据显示，尽管形态、生活史特征与生态偏好存在显著差异，TYP与LON型在遗传层面极为相似。但二者与SHA型的遗传差异均十分显著。基于包含3个基因区域的4286 bp串联数据集，这两个日本海带谱系可通过109个固定单核苷酸差异位点以及7个固定长度多态性位点加以区分。GenBank数据库显示，TYP与LON型与日本海带（S. japonica）亲缘关系紧密，而SHA型则与厚叶海带（S. cichorioides）亲缘相近。本研究使用的3种基因标记在藻类物种鉴定中灵敏度存在差异，其中COI基因的判别能力最强。然而，5’端COI“DNA条形码”区域（约650 bp）并不适用于物种鉴定，甚至可能产生误导，至少对于那些可能经历过历史杂交事件的藻类物种而言如此。
结论：考虑到表型可塑性在演化中的潜在作用，本研究认为TYP与LON型属于藻类表型多样化的实例，使其能够成功适应差异显著的浅海与深海海洋环境；而SHA型与厚叶海带（S. cichorioides）高度相似，应被视为独立物种。本文还简要探讨了该研究结果在藻类资源管理与保护中的实际应用价值。