Quaternary climate oscillations are a well‐known driver of animal diversification, but their effects are most well studied in areas where glaciations lead to habitat fragmentation. In large areas of the planet, however, glaciations have had the opposite effect, but here their impacts are much less well understood. This is especially true in Southeast Asia, where cyclical changes in land distribution have generated enormous land expansions during glacial periods. In this study, we selected a panel of five songbird species complexes covering a range of ecological specificities to investigate the effects Quaternary land bridges have had on the connectivity of Southeast Asian forest biota. Specifically, we combined morphological and bioacoustic analysis with an arsenal of population genomic and modelling approaches applied to thousands of genome‐wide DNA markers across a total of more than 100 individuals. Our analyses show that species dependent on forest understorey exhibit deep differentiation between Borneo and western Sundaland, with no evidence of gene flow during the land bridges accompanying the last 1–2 ice ages. In contrast, dispersive canopy species and habitat generalists have experienced more recent gene flow. Our results argue that there remains much cryptic species‐level diversity to be discovered in Southeast Asia even in well‐known animal groups such as birds, especially in nondispersive forest understorey inhabitants. We also demonstrate that Quaternary land bridges have not been equally suitable conduits of gene flow for all species complexes and that life history is a major factor in predicting relative population divergence time across Quaternary climate fluctuations.

中文翻译：

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第四纪陆桥还不是基因流动的通用管道。

第四纪气候振荡是动物多样化的众所周知的驱动力，但是在冰川作用导致栖息地破碎化的地区，对第四季度气候振荡的影响进行了最充分的研究。然而，在地球的大片地区，冰川作用却是相反的，但是在这里它们的影响却鲜为人知。在东南亚尤其如此，在冰川时期，土地分布的周期性变化导致了巨大的土地扩张。在这项研究中，我们选择了一个由五种鸣禽物种复合体组成的小组，它们涵盖了一系列生态特征，以研究第四纪陆桥对东南亚森林生物群系的连通性的影响。特别，我们将形态学和生物声学分析与大量种群基因组学和建模方法相结合，将其应用于总共100多个个体中的数千个全基因组DNA标记。我们的分析表明，依赖于森林底层的物种在婆罗洲和桑达兰西部之间表现出深层的分化，没有证据表明在最近的1-2个冰河时代伴随着陆桥的基因流动。相比之下，分散的树冠物种和栖息地通才则经历了最近的基因流动。我们的研究结果表明，即使在鸟类等著名的动物群体中，尤其是在非分散性森林底层居民中，东南亚仍存在许多隐性物种级别的多样性。