Islands were key to the development of allopatric speciation theory because they are a natural laboratory of repeated barriers to gene flow caused by open water gaps. Despite their proclivity for promoting divergence, little empirical work has quantified the extent of gene flow among island populations. Following classic island biogeographic theory, two metrics of interest are relative island size and distance. Fiji presents an ideal system for studying these dynamics, with four main islands that form two large‐small pairs. We sequenced thousands of ultraconserved elements (UCEs) of the Fiji bush‐warbler Horornis ruficapilla, a passerine distributed on these four Fijian islands, and performed a demographic analysis to test hypotheses of the effects of island size and distance on rates of gene flow. Our demographic analysis inferred low levels of gene flow from each large island to its small counterpart and little or none in the opposite direction. The difference in the distance between these two island pairs manifested itself in lower levels of gene flow between more distant islands. Both findings are generally concordant with classic island biogeography. The amount of reduction in gene flow based on distance was consistent with predictions from island biogeographic equations, while the reduction from small to large islands was possibly greater than expected. These findings offer a hypothesis and framework to guide future study of interisland gene flow in archipelagos as the study of island biogeography progresses into the genomic era.

中文翻译：

---

对岛屿生物地理学理论进行的用于估算斐济鸟类基因流量的测试在很大程度上与中性预期相符。

岛屿是异源物种形成理论发展的关键，因为它们是天然的实验室，可以对由于开放水隙造成的基因流的反复障碍进行反复研究。尽管它们倾向于促进分歧，但是很少的经验工作可以量化岛屿人群之间基因流动的程度。遵循经典的岛屿生物地理学理论，两个有趣的指标是相对岛屿大小和距离。斐济提供了研究这些动力学的理想系统，其中有四个形成两个大对小对的主要岛屿。我们对斐济丛林莺Horornis ruficapilla的数千个超保守元素（UCE）进行了测序，一个雀形目分布在这四个斐济群岛上，并进行了人口统计分析，以检验关于岛屿大小和距离对基因流动速率的影响的假设。我们的人口统计分析推断，从每个大岛到小岛的基因流量很低，而相反方向的基因流很少或根本没有。这两个岛对之间的距离差异表现为距离较远的岛之间的基因流动水平较低。这两个发现通常与经典的岛屿生物地理学相一致。基于距离的基因流减少量与岛屿生物地理方程式的预测一致，而从小岛到大岛的减少可能大于预期。