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: (i) characterize tempo and patterns of diversification; (ii) assess the impact of the EOEE; and (iii) 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, the diversification rate declined or did not shift following geographical 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 land masses of Earth.

分布范围扩张与伴随的物种分化之间的相互作用，是进化生物学家极为关注的核心问题，尤其当该过程与跨大陆扩散或大规模灭绝事件相关联时。真蛙类的演化历史以环全球分布范围扩张为典型特征。作为幸免于始新世-渐新世灭绝事件（EOEE）的演化支系，该类群为检验“分布范围扩张会提升净分化速率”这一预测提供了理想的研究体系。本研究构建了截至目前采样密度最高的时间校准系统发育树，以达成三个研究目标：（1）解析物种分化的速率与模式；（2）评估始新世-渐新世灭绝事件的影响；（3）检验“分布范围扩张后净分化速率提升”这一假说。研究结果显示，始新世晚期对全新生物地理区域的定殖并未受到EOEE的影响；且令人意外的是，全球范围的分布扩张并未伴随净分化速率的提升。与之相反，地理扩张后的分化速率要么出现下降，要么未发生显著变化。因此，真蛙类的分化演化历史与主流预期相悖——此前学界普遍认为两栖动物的净分化速率会随时间推移逐渐加快，或在分布范围扩张后得到提升。本研究结果反而表明，尽管真蛙类拥有动态的生物地理演化历史，但其在定殖地球主要陆块的过程中，物种分化速率始终保持相对稳定。