中文摘要：

探讨古气候波动（如更新世末期冰期）对典型生物的时空分布和有效种群大小变动的影响是生物地理学和进化遗传学的重要研究课题。本文利用线粒体cox2–3序列和RAPD两种分子标记,对分布于加拿大–西北大西洋地区8个地点（共138个个体）的掌形藻（Palmaria palmata）进行谱系地理学研究,试图阐明当更新世冰期来临时掌形藻如何衍生出适应性的进化机制,并形成当前的地理分布格局。结果表明,线粒体cox2–3间区序列共检测出11个单倍型,其中1个单倍型（C3）在所有种群中都有分布,并位于星状基因谱系的中心位置,可认为是祖先单倍型。St.Lawrence湾内北部的两个种群多样性最高,与其他地理种群分化最明显,这与基于RAPD数据的STRUCTURE聚类分析结果相一致。根据掌形藻遗传多样性及其单倍型谱系结构特征,推测掌形藻在加拿大–西北大西洋沿岸存在多个冰期避难所。分子多态性分析（AMOVA）显示掌形藻的遗传变异主要来自种群内,而St.Lawrence湾和Fundy湾群组间的遗传变异较小。cox2–3序列的Bayesianskylineplots分析结果反映出掌形藻种群在加拿大–西北大西洋沿岸经历了轻微的种群扩张,时间大概在0.18–0.13百万年前。St.Lawrence湾和Fundy湾群组间的K2P遗传距离为0.2%,相应的分化时间大约在0.36百万年前。由此推测,更新世末期的冰期及间冰期是影响掌形藻种群结构及变动的重要古气候环境因子。

英文摘要：

The paleoclimate change （e.g. the glacial fluctuation in the late Pleistocene） played an important role in shaping species’ population genetic structure, geographic distribution patterns, and gradient of diversity and composition. In this study, we sampled eight populations （138 individuals） of Palmaria palmata, a commercially and ecologically important red macroalga found on both sides of the North Atlantic coast, aiming to assess the genetic structure and demographic history through the integration of mitochondrial cox2–3 spacer and RAPD variation. Eleven mtDNA cox2–3 haplotypes were detected, one of which （C3） was common and located centrally in a haplotype network. It is shared by all populations and is regarded as ancestral. Two northern populations from the Gulf of St. Lawrence had highest levels of genetic diversity, and were significantly divergent from all other populations. AMOVA showed that highest genetic variation for cox2–3 occurred within populations, while less existed among groups. This was consistent with the results of a STRUCTURE clustering analysis of RAPD data. Our genetic diversity and haplotype network analyses indicated that multiple glacial refugia might have existed for the species along the Canada–north-west Atlantic coast. Furthermore, Bayesian skyline plot analysis based on cox2–3 spacer sequences indicated that population size underwent a slight increase over temporal and spatial scales. This occurred in approximately 0.18–0.13 million years ago. Pairwise genetic distance （K2P） between populations from the Gulf of St. Lawrence and the Bay of Fundy was 0.2%, indicating that they diverged from their common ancestor since about 0.36 million years ago. The evidence from our study suggests that climatic oscillations during the late Pleistocene had a drastic influence on the demography and genetic diversity of P. palmata in the Canada–northwest Atlantic.