Graduate School of Human and Environmental Studies, Kyoto University , Yoshida Nihonmatsucho, Sakyo, Kyoto 606-8501 , Japan.
AoB Plants. 2011;2011:plr021. doi: 10.1093/aobpla/plr021. Epub 2011 Aug 9.
Lake Biwa is one of the world's few ancient lakes. Formed ∼4 million years ago, the lake harbours many coastal species that commonly inhabit seashores. The beach pea Lathyrus japonicus is a typical coastal species of this freshwater lake, but its inland populations are faced with the threat of extinction. Here, we investigated the phylogeographical and population structures of both inland and coastal populations of L. japonicus. We also elucidated the historical isolation of the Lake Biwa population.
In total, 520 individuals from 50 L. japonicus populations were sampled throughout the species distribution in Japan. Chloroplast haplotyping using intergenic spacers psbA-trnH and atpI-atpH was performed to investigate the phylogeographical structure as well as the genetic diversity of L. japonicus. Six nuclear microsatellite markers were also used to analyse the population structure.
Population structure analyses of chloroplast DNA (cpDNA) and nuclear DNA (nDNA) identified inland and coastal groups. Based on the genetic differentiation, inland populations exhibited a single cpDNA haplotype and significantly lower values of H(S), AR and F(IS) than coastal populations. In addition to the presence of a bottleneck, the lack of gene flow among inland populations was supported by estimates of recent migration rates between subpopulations.
Our data revealed that inland populations have been isolated in Lake Biwa as 'landlocked' populations since the predecessor lake was isolated from sea. This was also seen in a previous study of Calystegia soldanella. However, the high genetic differentiation, accompanied by a lack of gene flow among the Lake Biwa populations (according to the BAYESASS(+) analysis), contradicts the results with C. soldanella. We conclude that because of the presence of a bottleneck and low genetic diversity of the inland populations, self-sustaining population persistence may be difficult in the future. Conservation strategies must consider the genetic properties of such isolated populations.
琵琶湖是世界上少数几个古老湖泊之一。该湖形成于约 400 万年前，拥有许多常见于海滨的沿海物种。滨藜 Lathyrus japonicus 是该淡水湖中一种典型的沿海物种，但它的内陆种群正面临灭绝的威胁。在这里，我们调查了内陆和沿海种群的 L. japonicus 的系统地理结构和种群结构。我们还阐明了琵琶湖种群的历史隔离。
我们在日本整个物种分布范围内共采集了 50 个 L. japonicus 种群的 520 个个体。我们使用质体间隔区 psbA-trnH 和 atpI-atpH 进行叶绿体单倍型分析，以研究 L. japonicus 的系统地理结构和遗传多样性。我们还使用了 6 个核微卫星标记来分析种群结构。
叶绿体 DNA (cpDNA) 和核 DNA (nDNA) 的种群结构分析确定了内陆和沿海群体。基于遗传分化，内陆种群表现出单一的 cpDNA 单倍型，其 H(S)、AR 和 F(IS) 值显著低于沿海种群。除了瓶颈效应之外，亚种群间近期迁移率的估计也支持内陆种群之间缺乏基因流。
我们的数据表明，自前湖与海洋隔绝以来，内陆种群就已经在琵琶湖中被隔离为“内陆”种群。这在之前对 Calystegia soldanella 的研究中也有发现。然而，高遗传分化伴随着湖内种群之间缺乏基因流（根据 BAYESASS(+)分析），这与 C. soldanella 的结果不一致。我们得出结论，由于存在瓶颈和内陆种群遗传多样性低，未来这些种群可能难以自我维持。保护策略必须考虑到这些隔离种群的遗传特性。
