Table_2_Biogeographic Population Structure of Chimeric Blades of Porphyra in the Northeast Atlantic Reveals Southern Rich Gene Pools, Introgression and Cryptic Plasticity.docx

The genus Porphyra sensu lato (Bangiaceae, Rhodophyta), an important seaweed grown in aquaculture, is the most genetically diverse group of the Class Bangiophyceae, but has poorly understood genetic variability linked to complex evolutionary processes. Genetic studies in the last decades have largely focused on resolving gene phylogenies; however, there is little information on historical population biogeography, structure and gene flow in the Bangiaceae, probably due to their cryptic nature, chimerism and polyploidy, which render analyses challenging. This study aims to understand biogeographic population structure in the two abundant Porphyra species in the Northeast Atlantic: Porphyra dioica (a dioecious annual) and Porphyra linearis (protandrous hermaphroditic winter annual), occupying distinct niches (seasonality and position on the shore). Here, we present a large-scale biogeographic genetic analysis across their distribution in the Northeast Atlantic, using 10 microsatellites and cpDNA as genetic markers and integrating chimerism and polyploidy, including simulations considering alleles derived from different ploidy levels and/or from different genotypes within the chimeric blade. For P. linearis, both markers revealed strong genetic differentiation of north-central eastern Atlantic populations (from Iceland to the Basque region of Northeast Iberia) vs. southern populations (Galicia in Northwest Iberia, and Portugal), with higher genetic diversity in the south vs. a northern homogenous low diversity. For. P. dioica, microsatellite analyses also revealed two genetic regions, but with weaker differentiation, and cpDNA revealed little structure with all the haplotypes mixed across its distribution. The southern cluster in P. linearis also included introgressed individuals with cpDNA from P. dioica and a winter form of P. dioica occurred spatially intermixed with P. linearis. This third entity had a similar morphology and seasonality as P. linearis but genomes (either nuclear or chloroplast) from P. dioica. We hypothesize a northward colonization from southern Europe (where the ancestral populations reside and host most of the gene pool of these species). In P. linearis recently established populations colonized the north resulting in homogeneous low diversity, whereas for P. dioica the signature of this colonization is not as obvious due to hypothetical higher gene flow among populations, possibly linked to its reproductive biology and annual life history.

广义紫菜属（Porphyra sensu lato，隶属于红藻门（Rhodophyta）紫菜科（Bangiaceae））是一种重要的养殖海藻，同时也是红毛菜纲（Bangiophyceae）中遗传多样性最高的类群，但其与复杂演化过程相关的遗传变异机制仍未得到充分阐明。近几十年来的遗传学研究大多聚焦于解析基因系统发育关系；然而，学界对紫菜科的历史种群生物地理学、种群结构以及基因流的相关信息仍十分匮乏，这大概率源于其隐存特性、嵌合现象与多倍性，这些特征极大增加了相关分析的难度。本研究旨在解析东北大西洋海域两种优势紫菜属物种的生物地理学种群结构：分别是雌雄异株一年生种双性紫菜（Porphyra dioica），以及雄性先熟雌雄同株的冬生一年生种类线形紫菜（Porphyra linearis），二者占据不同的生态位（季相分布与潮间带位置均存在差异）。本研究针对这两个物种在东北大西洋的整个分布范围开展了大规模生物地理学遗传分析：以10个微卫星（microsatellite）标记与叶绿体DNA（cpDNA）作为遗传标记，并整合嵌合现象与多倍性因素，其中模拟分析涵盖了源自不同倍性水平的等位基因，以及嵌合藻体内部不同基因型的等位基因。针对线形紫菜，两种标记均揭示了东大西洋中北部种群（从冰岛到东北伊比利亚的巴斯克地区）与南部种群（伊比利亚西北部的加利西亚与葡萄牙）之间存在显著的遗传分化；南部种群的遗传多样性更高，而北部种群则呈现出同质化且多样性较低的特征。而对于双性紫菜，微卫星分析同样揭示了两个遗传区域，但分化程度较弱；叶绿体DNA分析则未发现明显的种群结构，所有单倍型在其分布范围内均呈混合状态。线形紫菜的南部类群中还包含了携带来自双性紫菜叶绿体DNA的渐渗个体，同时一种双性紫菜的冬生型在空间分布上与线形紫菜相互混杂。这一第三类群与线形紫菜具有相似的形态特征与季相分布，但其基因组（无论是核基因组还是叶绿体基因组）均源自双性紫菜。我们提出如下假说：该类群的祖先种群栖息于南欧，并承载了这两个物种的大部分基因库，物种整体是从南欧向北进行拓殖的。对于线形紫菜，新近在北部建立的种群呈现出同质化且多样性较低的特征；而双性紫菜的拓殖痕迹则并不明显，这可能与其种群间较高的假想基因流有关，而这一特征或许与其生殖生物学特性以及一年生生活史相关。