Data from: Did True Frogs “dispersify”?

The interplay between range expansion and concomitant diversification is of fundamental interest to evolutionary biologists, particularly when linked to intercontinental dispersal and/or large scale extinctions. The evolutionary history of True Frogs has been characterized by circumglobal range expansion. As a lineage that survived the Eocene-Oligocene extinction event (EOEE), the group provides an ideal system to test the prediction that range expansion triggers increased net-diversification. We constructed the most densely sampled, time-calibrated phylogeny to date in order to: (1) characterize tempo and patterns of diversification; (2) assess the impact of the EOEE; and (3) test the hypothesis that range expansion was followed by increased net-diversification. We show that late Eocene colonization of novel biogeographic regions was not affected by the EOEE and surprisingly, global expansion was not followed by increased net-diversification. On the contrary, diversification rate declined or did not shift following geographic expansion. Thus, the diversification history of True Frogs contradicts the prevailing expectation that amphibian net-diversification accelerated towards the present or increased following range expansion. Rather, our results demonstrate that despite their dynamic biogeographic history, True Frogs diversified at a relatively constantly rate, even as they colonized the major landmasses of Earth.

分布范围扩张（range expansion）与伴随的物种分化之间的相互作用，是进化生物学家的核心研究议题，尤其当该过程与洲际扩散或大规模灭绝事件相关联时。真蛙类（True Frogs）的演化历史以环全球分布范围扩张为典型特征。作为一支在始新世-渐新世灭绝事件（Eocene-Oligocene Extinction Event, EOEE）中幸存的演化支，该类群为检验“分布范围扩张会提升净物种分化速率（net-diversification）”这一预测提供了理想的研究体系。本研究构建了迄今为止采样密度最高的时间校准系统发育树（time-calibrated phylogeny），以期达成以下目标：(1) 刻画物种分化的速率模式与演化格局；(2) 评估始新世-渐新世灭绝事件的影响；(3) 检验“分布范围扩张后净物种分化速率提升”这一假说。研究结果显示，始新世晚期对新生生物地理区域的殖民并未受到始新世-渐新世灭绝事件的影响；且令人意外的是，全球范围扩张并未伴随净物种分化速率的提升。反之，地理扩张之后物种分化速率反而下降，或未发生显著变化。因此，真蛙类的物种分化历史与主流预期相悖——此前学界认为两栖动物的净物种分化速率会随时间推移而加快，或在分布范围扩张后提升。与之相反，本研究结果表明，尽管真蛙类具备活跃的生物地理演化历史，但其在殖民地球各主要大陆的过程中，物种分化速率始终维持相对恒定的水平。