Table_1_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）红毛菜科（Bangiaceae））是一类重要的水产养殖海藻，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被充分阐明。近数十年来的遗传学研究大多聚焦于解析物种的基因系统发育关系，但目前关于红毛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，这可能源于该类群所具有的隐存种特性、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：分别为雌雄异株一年生的Porphyra dioica，以及雄性先熟的雌雄同体冬季一年生的Porphyra linearis，二者占据不同的生态位（表现为季节性与潮间带栖息位置的差异）。本研究依托10个微卫星标记（microsatellites）与叶绿体DNA（cpDNA）作为遗传标记，整合嵌合现象与多倍性特征开展了跨东北大西洋全分布区的大规模生物地理学遗传分析，其中还包含针对不同倍性水平等位基因、以及嵌合叶状体中不同基因型等位基因的模拟分析。针对Porphyra linearis，两种标记均揭示出显著的遗传分化：东大西洋中北部种群（分布范围从冰岛延伸至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地区与葡萄牙）之间存在明显分化，且南部种群的遗传多样性显著高于北部同质化的低遗传多样性种群。针对Porphyra dioica，微卫星分析同样揭示出两个遗传区域，但分化程度较弱；而叶绿体DNA分析则未发现明显的种群结构，所有单倍型在其分布区内均呈混合状态。Porphyra linearis的南部种群中还包含了来自Porphyra dioica的叶绿体DNA渐渗个体，同时在空间分布上与Porphyra dioica的冬季型种群存在重叠。这一第三类群在形态与季节性特征上与Porphyra linearis相似，但其细胞核或叶绿体基因组却源自Porphyra dioica。我们提出如下假说：上述两个物种均起源于南欧（该区域存在祖先种群并承载了两个物种的大部分基因库），并向北完成殖民扩散。对于Porphyra linearis而言，新近建立的北部种群遗传同质化程度高且多样性较低；而Porphyra dioica则未呈现出明显的殖民扩散遗传信号，这可能源于其种群间更高的基因流水平，而该特征或许与其生殖生物学特性以及一年生生活史相关。