Department of Zoology, Edward Grey Institute of Field Ornithology, University of Oxford, Oxford, OX1 3PS, UK.
Department of Biology, Colorado State University, Fort Collins, CO, USA.
Heredity (Edinb). 2020 Apr;124(4):535-549. doi: 10.1038/s41437-020-0298-8. Epub 2020 Feb 20.
Theory predicts that when populations are established by few individuals, random founder effects can facilitate rapid phenotypic divergence even in the absence of selective processes. However, empirical evidence from historically documented colonisations suggest that, in most cases, drift alone is not sufficient to explain the rate of morphological divergence. Here, using the human-mediated introduction of the silvereye (Zosterops lateralis) to French Polynesia, which represents a potentially extreme example of population founding, we reassess the potential for morphological shifts to arise via drift alone. Despite only 80 years of separation from their New Zealand ancestors, French Polynesian silvereyes displayed significant changes in body and bill size and shape, most of which could be accounted for by drift, without the need to invoke selection. However, signatures of selection at genes previously identified as candidates for bill size and body shape differences in a range of bird species, also suggests a role for selective processes in driving morphological shifts within this population. Twenty-four SNPs in our RAD-Seq dataset were also found to be strongly associated with phenotypic variation. Hence, even under population founding extremes, when it is difficult to reject drift as the sole mechanism based on rate tests of phenotypic shifts, the additional role of divergent natural selection in novel environments can be revealed at the level of the genome.
理论预测，当种群由少数个体建立时，随机的奠基者效应即使在没有选择过程的情况下，也能促进快速的表型分化。然而，来自历史记录的殖民化的经验证据表明，在大多数情况下，仅仅是漂变本身不足以解释形态分化的速度。在这里，我们利用人类介导的银眼（Zosterops lateralis）向法属波利尼西亚的引入，这代表了种群建立的一个潜在极端的例子，重新评估了通过漂变单独产生形态变化的可能性。尽管与它们的新西兰祖先分离了 80 年，但法属波利尼西亚的银眼在身体和喙的大小和形状上显示出了显著的变化，其中大部分可以归因于漂变，而不需要援引选择。然而，在一系列鸟类物种中被确定为喙大小和体型差异候选基因的选择信号，也表明选择过程在驱动该种群的形态变化方面起着作用。我们的 RAD-Seq 数据集的 24 个 SNPs 也被发现与表型变异有很强的相关性。因此，即使在种群建立的极端情况下，当基于表型变化的速率检验很难拒绝漂变作为唯一机制时，在基因组水平上可以揭示在新环境中发散的自然选择的额外作用。
