Tectonic collision and uplift of Wallacea triggered the global songbird radiation

Songbirds (oscine passerines) are the most species rich and cosmopolitan bird group, comprising almost half of global avian species diversity. Because of their diversity and ubiquity, songbirds are used extensively in studies of evolutionary ecology, diversification, and ethology. Songbirds originated in Australia, but the evolutionary trajectory from a single species in an isolated continent to worldwide proliferation is poorly understood. Prior research suggested songbird diversification scenarios that are largely uncoupled from Earth history, including extensive diversification of lineages in New Guinea prior to its emergence as a landmass and long-distance dispersal to Africa or Asia when no dispersal corridors existed. However, these results may be flawed because the studies relied on unresolved phylogenetic relationships and a controversial biogeographic time calibration. Here, we combine the first genome-scale DNA sequence data set for songbirds, fossil-based time calibrations, and geologically informed biogeographic reconstructions to provide the first well-supported evolutionary hypothesis for the group. We show that songbird diversification began in the Oligocene, but accelerated in the early Miocene, at approximately half the age of most previous estimates. This burst of diversification occurred after island formation in Wallacea, which provided the first dispersal corridor out of Australia, and resulted in independent waves of songbird expansion through Asia to the rest of the globe. Although New Guinea presently contains high songbird species richness, our data unambiguously falsify the proto-Papuan hypothesis for early songbird diversification2,6 and suggest that New Guinea has, instead, served as an “evolutionary refuge” for Australian lineages that have diversified more recently within the island23. Our results reconcile songbird evolution with Earth history and link a major radiation of terrestrial biodiversity to early diversification within an isolated Australian continent.

鸣禽（oscine passerines）是物种最为丰富、分布最广的鸟类类群，约占全球鸟类物种多样性的半数。鉴于其类群多样性与分布普遍性，鸣禽被广泛应用于进化生态学、物种分化及行为学研究领域。鸣禽起源于澳大利亚，但从孤立大陆上的单一祖先物种演变为全球广布类群的演化轨迹，迄今尚未得到清晰阐释。既往研究提出的鸣禽物种分化模式，大多与地球历史进程脱节——包括新几内亚在形成陆块前就发生了大规模支系分化，以及在不存在扩散通道的情况下长距离扩散至非洲与亚洲。然而，这些研究结论可能存在缺陷，因其均依赖分辨率不足的系统发育关系，以及存在争议的生物地理时间校准方案。
本研究结合了首个全基因组规模的鸣禽DNA序列数据集、基于化石记录的时间校准方案，以及结合地质学证据的生物地理重建分析，首次为该类群构建了得到充分支持的演化假说。研究显示，鸣禽的物种分化始于渐新世，但在中新世早期显著加速，其分化发生的时间约为多数此前估算的一半。这一轮物种分化爆发发生在华莱士区（Wallacea）形成岛屿之后——该区域为鸣禽提供了首个离开澳大利亚的扩散通道，并推动鸣禽通过亚洲向全球其余地区展开多波独立的扩张进程。
尽管当前新几内亚拥有极高的鸣禽物种丰富度，但本研究数据明确证伪了早期鸣禽物种分化的原巴布亚假说（proto-Papuan hypothesis）2,6，并指出新几内亚实际上更像是近期在岛内发生分化的澳大利亚支系的"演化避难所"23。本研究结果将鸣禽演化与地球历史进程相契合，并将陆地生物多样性的一次主要辐射演化事件，与孤立澳大利亚大陆上的早期物种分化建立了关联。