实验海洋生物学重点实验室知识库

摘 要

西北太平洋拥有丰富的海洋生物多样性，第四纪末期以来冰期-间冰期所介导的海岸线变迁，使其成为海洋生物物种形成和群体遗传多样性研究的热点区域之一。随着全球气候变化和人类活动加剧，西北太平洋地区的物种分布范围不断缩小、多样性不断遭到破坏，对海洋生物资源开展保护研究刻不容缓。真江蓠Agarophyton vermiculophyllum (Ohmi) Gurgel, J.N. Norris et Fredericq原产于西北太平洋，在分类学上隶属于红藻门（Rhodophyta），真红藻纲（Florideophyceae），江蓠目（Gracilariales），江蓠科（Gracilariaceae），Agarophyton属，具有重要的生态和经济价值。真江蓠也因其在欧洲和北美的大范围入侵而引起广泛的研究兴趣。然而，目前关于西北太平洋地区真江蓠的谱系地理结构和群体遗传多样性等信息尚不明确。在本研究中，我们采用线粒体细胞色素氧化酶第一亚基（cox1）和微卫星（SSR）研究西北太平洋真江蓠谱系地理模式和群体遗传分化特征，主要结果如下：

（1）我们利用cox1片段（1214bp）分析西北太平洋地区48个真江蓠群体（611个体）的谱系地理模式、群体多样性和遗传分化，发现其总体呈现高单倍型多样性（H_d=0.6632）和低核苷酸多样性（π=0.2473×10^{- 2}）的特点，其中日本群体具有最高的遗传多样性。基于贝叶斯法（Bayesian Inference，BI）和最大似然法（Maximum Likelihood，ML）构建的cox1单倍型系统进化树显示在西北太平洋真江蓠已分化为五个遗传谱系，且谱系之间分化显著，分化时间约在0.02~0.05 Ma。在48个真江蓠群体间，大部分遗传分化显著（70.8%F_st>0.25，p<0.05）。S-DIVA分析显示，西北太平洋地区真江蓠的祖先在冰期广泛分布于日本太平洋沿岸、东海（冲绳海槽）和南海等三个生物地理区。这些综合证据表明在西北太平洋第四纪末期气候振荡期间，真江蓠可能在多个分散的冰期避难所中存留下来。

（2）我们利用10对微卫星（SSR）对西北太平洋地区38个真江蓠群体（555个体）进行遗传结构和多样性分析。共获得126个等位基因，各位点的平均有效等位基因为4.290，其它各项遗传参数较小，表明西北太平洋真江蓠群体遗传多样性偏低。群体内近交系数F_is（0.3455）和群体间近交系数F_it（0.7303）表明西北太平洋真江蓠群体存在一定程度的近交，具有杂合子缺失现象。Structure结构分析显示真江蓠分为四个遗传组，特别是在山东半岛东南部检测到少见的遗传隔离，日本海和日本群体聚为一个遗传组且遗传混杂明显。F_st（0.5879）、Nei’s遗传距离和基因流（N_m=0.1752）显示西北太平洋真江蓠群体间分化显著但基因流有限。除西北太平洋古气候和洋流因素外，真江蓠的这些遗传特征可能与其生殖模式、微地理环境的选择压力和人类活动有关。

本研究系统阐述了西北太平洋地区真江蓠群体遗传结构、多样性特征和遗传变异的时空分布模式，并解释了这种谱系地理模式形成的潜在因素。相关结果不仅为后续研究真江蓠的入侵路径和遗传机制奠定基础，而且为其自然资源保护和管理提供了科学依据。

Abstract

The northwest Pacific is one of the regions with the richest marine biodiversity in the world, and the repeated transgression and regression of coastlines mediated by the late Quaternary glacial-interglacial cycles make this region a hotspot to study marine speciation and population genetic diversity. With the interference of global climate change and anthropogenic activities, the distribution ranges of species in the northwest Pacific are shrinking and the diversity levels are being destroyed continuously, highlighting the importance and necessity of conserving natural marine resources. The red alga Agarophyton vermiculophyllum (Ohmi) Gurgel, J.N. Norris et Fredericq is a commercially and ecologically important foundation species native to the northwest Pacific, and it taxonomically belongs to Agarophyton, Gracilariaceae, Gracilariales, Florideophyceae, Rhodophyta. In addition, A. vermiculophyllum has caught extensive research interest because of its widespread invasion in Europe and North America. However, the knowledge of phylogeographic structure and genetic diversity across the entire native range are still scarce. In this study, we used mitochondrial cytochrome c oxidase subunit 1 (cox1) and microsatellite (SSR) to explore phylogeographic patterns and population genetic differentiation of A. vermiculophyllum in the northwest Pacific. The main results are as follows:

1. We used cox1 sequence (1214bp) to explore the phylogeographic patterns, population diversity and genetic differentiation of 48 A. vermiculophyllum populations (611 individuals) in the northwest Pacific. The results showed high haplotype diversity (H_d=0.6632) and low nucleotide diversity (π=0.2473×10^-2) in A. vermiculophyllum in the northwest Pacific, and the Japanese populations had the highest genetic diversity. The phylogenetic analysis of cox1 haplotypes based on Bayesian Inference (BI) and Maximum Likelihood (ML) consistently revealed five phylogeographically structured genetic lineages that diverged significantly from each other. The divergence time among the five genetic lineages varied from 0.02 to 0.05 Ma. Among all pairwise comparisons of 48 populations, most were differentiated significantly (70.8% F_st>0.25, p<0.05). S-DIVA analyses showed that the ancestors of A. vermiculophyllum in the northwest Pacific was widely distributed in three biogeographic areas including the Japan-Pacific coast, the East China Sea (Okinawa trough) and the South China Sea during the ice age. These combined evidence indicate that A. vermiculophyllum might have survived in multiple scattered glacial refugia during the late Quaternary climate oscillations in the northwest Pacific.

2. We additionally used 10 microsatellites (SSR) to explore the genetic structure and diversity of 38 A. vermiculophyllum populations (555 individuals) in the northwest Pacific. Totally, 126 alleles were obtained with an average effective allele of 4.290, and small values of other genetic parameters indicate a relatively low genetic diversity in A. vermiculophyllum in the northwest Pacific. F_is (0.3455) and F_it (0.7303) indicated a certain degree of inbreeding and heterozygote loss. Structure analysis detected four genetic groups. In particular, a rare genetic isolationwas found in the southeast of Shandong peninsula, and the sea of Japan and the Japanese population clustered into a genetic group with obvious genetic mixing. F_st (0.5879), Nei’s genetic distance and N_m (0.1752) showed significant genetic differentiation and weak gene flow between A. vermiculophyllum populations. In addition to palaeoclimate oscillations and ocean current, reproduction patterns, selection pressure imposed by microgeographical environmental variables and human interference may be related to these genetic characteristics detected in A. vermiculophyllum in the northwest Pacific .

   This study systematically described population genetic structure, diversity and temporal-spatial lineage distribution of A. vermiculophyllum in the northwest Pacific, including the underlying factors contributing to such a distribution pattern. The results not only lay a foundation for further exploring the invasion route and genetic mechanism of A. vermiculophyllum inhabiting different ecological niches, but also provide scientific basis for conserving and managing natural resources of it.