Divergent selection and drift shape the genomes of two avian sister species spanning a saline–freshwater ecotone
Divergent selection and drift shape the genomes of two avian sister species spanning a saline–freshwater ecotone
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DOI：
10.1002/ece3.5804
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发表时间：
2018-06
影响因子：
2.6
通讯作者：
J. Walsh;Gemma V. Clucas;M. MacManes;W. K. Thomas;Adrienne I. Kovach
中科院分区：
文献类型：
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作者：
J. Walsh;Gemma V. Clucas;M. MacManes;W. K. Thomas;Adrienne I. Kovach
基于生态的趋异选择（或生态物种形成）导致的物种趋异在产生和维持生物多样性方面的作用是进化生物学的一个中心问题。比较跨越选择性栖息地梯度的系统发育相关类群的基因组，能够发现选择的不同特征，从而为物种形成中不同生态选择的作用提供有价值的见解。潮汐沼泽生态系统为研究生物体对生态分化造成的选择压力的适应提供了易于处理的机会。潮汐沼泽内咸水-淡水交错带的急剧环境梯度给陆地脊椎动物带来了极大的适应性挑战。在这里，我们对潮汐沼泽特有的两种鸟类姊妹物种——盐沼麻雀 (Ammodramus caudacutus) 和纳尔逊麻雀 (A. nelsoni) 的 20 个全基因组进行了测序，以评估选择性和人口统计过程对形成全基因组分化模式的影响。这两个最近分化的姐妹物种之间的全基因组差异非常高（全基因组 FST = 0.32）。在全基因组高度分化的背景下，高度分化的区域广泛分布在整个基因组中，而不是集中在分化岛内。这些模式可能是过去潮汐行军殖民事件中遗传漂变以及对不同环境的不同选择的结果。我们确定了几个候选基因，这些基因在盐沼麻雀和尼尔森麻雀之间表现出较高的差异，包括与渗透调节、昼夜节律和羽毛黑化有关的基因——所有假定的候选基因都与适应潮汐沼泽环境有关。这些发现为发散选择和遗传漂变在产生和维持生物多样性中的作用提供了新的见解。
The role of species divergence due to ecologically-based divergent selection – or ecological speciation – in generating and maintaining biodiversity is a central question in evolutionary biology. Comparison of the genomes of phylogenetically related taxa spanning a selective habitat gradient enables discovery of divergent signatures of selection and thereby provides valuable insight into the role of divergent ecological selection in speciation. Tidal marsh ecosystems provide tractable opportunities for studying organisms’ adaptations to selective pressures that underlie ecological divergence. Sharp environmental gradients across the saline-freshwater ecotone within tidal marshes present extreme adaptive challenges to terrestrial vertebrates. Here we sequence 20 whole genomes of two avian sister species endemic to tidal marshes – the Saltmarsh Sparrow (Ammodramus caudacutus) and Nelson’s Sparrow (A. nelsoni) – to evaluate the influence of selective and demographic processes in shaping genome-wide patterns of divergence. Genome-wide divergence between these two recently diverged sister species was notably high (genome-wide FST = 0.32). Against a background of high genome-wide divergence, regions of elevated divergence were widespread throughout the genome, as opposed to focused within islands of differentiation. These patterns may be the result of genetic drift acting during past tidal march colonization events in addition to divergent selection to different environments. We identified several candidate genes that exhibited elevated divergence between Saltmarsh and Nelson’s sparrows, including genes linked to osmotic regulation, circadian rhythm, and plumage melanism – all putative candidates linked to adaptation to tidal marsh environments. These findings provide new insights into the roles of divergent selection and genetic drift in generating and maintaining biodiversity.