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首页> 外文期刊>Marine biology >Present-day genetic composition suggests contrasting demographic histories of two dominant chaetognaths of the North-East Atlantic, Sagitta elegans and S. setosa
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Present-day genetic composition suggests contrasting demographic histories of two dominant chaetognaths of the North-East Atlantic, Sagitta elegans and S. setosa

机译：今天的遗传组成表明，东北大西洋的两个主要驼背象虫（Sagitta elegans）和S. setosa的人口统计学差异。

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Sagitta elegans and S. setosa are the two dominant chaetognaths in the North-East (NE) Atlantic. They are closely related and have a similar ecology and life history, but differ in distributional ranges. Sagitta setosa is a typical neritic species occurring exclusively above shelf regions, whereas S. elegans is a more oceanic species with a widespread distribution. We hypothesised that neritic species, because of smaller and more fragmented populations, would have been more vulnerable to population bottlenecks resulting from range contractions during Pleistocene glaciations than oceanic species. To test this hypothesis we compared mitochondrial Cytochrome Oxidase II DNA sequences of S. elegans and S. setosa from sampling locations across the NE Atlantic. Both species displayed very high levels of genetic diversity with unique haplotypes for every sequenced individual and an approximately three times higher level of nucleotide diversity in 5. elegans (0.061) compared to S. setosa (0.021). Sagitta setosa mitochondrial DNA (mtDNA) haplotypes produced a star-like phylogeny and a uni-modal mismatch distribution indicative of a bottleneck followed by population expansion. In contrast, S. elegans had a deeper mtDNA phylogeny and a multi-modal mismatch distribution as would be expected from a more stable population. Neutrality tests indicated that assumptions of the standard neutral model were violated for both species and results from the McDonald-Kreitman test suggested that selection played a role in the evolution of their mitochondrial DNA. Congruent with these results, both species had much smaller effective population sizes estimated from genetic data when compared to census population sizes estimated from abundance data, with a factor of ～10~8-10~9 difference. Assuming that selective effects are comparable for the two species, we conclude that the difference in genetic signature can only be explained by contrasting demographic histories. Our data are consistent with the hypothesis that in the NE Atlantic, the neritic S. setosa has been more severely affected by population bottlenecks resulting from Pleistocene range shifts than the more oceanic S. elegans.
机译：线虫和set.Sosa是北美东北大西洋地区的两个主要cha目鱼。它们密切相关，具有相似的生态和生活史，但分布范围不同。刚毛箭叶虫是典型的仅在架子区域上方的入侵物种，而线虫是一种海洋性较广的物种，分布广泛。我们假设，由于更新世冰期期间范围缩小而导致的种群瓶颈比海洋物种更小，因此种群数量较少且分散程度更高。为了验证这一假设，我们比较了来自东北大西洋沿线采样点的线虫和setosa线粒体细胞色素氧化酶II DNA序列。这两个物种都显示出很高的遗传多样性水平，每个测序个体都有独特的单倍型，并且线虫中的核苷酸多样性水平（0.061）大约比setosa S.（0.021）高三倍。矢状线虫线粒体DNA（mtDNA）单倍型产生星形系统发育和单峰不匹配分布，表明出现瓶颈，随后种群扩大。相反，秀丽隐杆线虫具有更深的mtDNA系统发育和多模式错配分布，这是更稳定的种群所期望的。中性测试表明两种物种均违反了标准中性模型的假设，麦当劳-克雷特曼测试的结果表明选择在其线粒体DNA的进化中起作用。与这些结果一致，与根据丰度数据估算的普查人口规模相比，这两种物种的遗传数据估算的有效种群数量要小得多，相差约10〜8-10〜9。假设这两种物种的选择性作用相当，我们得出的结论是，遗传特征的差异只能通过对比人口统计学历史来解释。我们的数据与这样的假说相符：在东北大西洋，与更新世的线虫相比，更新世的范围变化所导致的种群瓶颈更严重地影响着刚毛状的S. setosa。

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