CNRS, UMR 5554 Institut des Sciences de l'Evolution de Montpellier (Université de Montpellier), 34095 Montpellier, France;
Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Proc Natl Acad Sci U S A. 2020 Nov 17;117(46):28867-28875. doi: 10.1073/pnas.2005571117. Epub 2020 Nov 2.
Competition among species and entire clades can impact species diversification and extinction, which can shape macroevolutionary patterns. The fossil record shows successive biotic turnovers such that a dominant group is replaced by another. One striking example involves the decline of gymnosperms and the rapid diversification and ecological dominance of angiosperms in the Cretaceous. It is generally believed that angiosperms outcompeted gymnosperms, but the macroevolutionary processes and alternative drivers explaining this pattern remain elusive. Using extant time trees and vetted fossil occurrences for conifers, we tested the hypotheses that clade competition or climate change led to the decline of conifers at the expense of angiosperms. Here, we find that both fossil and molecular data show high congruence in revealing 1) low diversification rates, punctuated by speciation pulses, during warming events throughout the Phanerozoic and 2) that conifer extinction increased significantly in the Mid-Cretaceous (100 to 110 Ma) and remained high ever since. Their extinction rates are best explained by the rise of angiosperms, rejecting alternative models based on either climate change or time alone. Our results support the hypothesis of an active clade replacement, implying that direct competition with angiosperms increased the extinction of conifers by pushing their remaining species diversity and dominance out of the warm tropics. This study illustrates how entire branches on the Tree of Life may actively compete for ecological dominance under changing climates.
物种和整个进化枝之间的竞争会影响物种多样化和灭绝，从而影响宏观进化模式。化石记录显示，连续的生物更替，使主导群体被另一个群体所取代。一个引人注目的例子是裸子植物的衰落和被子植物在白垩纪的快速多样化和生态主导地位。人们普遍认为被子植物战胜了裸子植物，但解释这种模式的宏观进化过程和替代驱动因素仍不清楚。利用现生的时间树和经过验证的针叶树化石记录，我们检验了以下假设：是进化枝竞争还是气候变化导致了针叶树的衰落，从而使被子植物受益。在这里，我们发现化石和分子数据都高度一致地揭示了 1）在整个显生宙的变暖事件中，多样化率较低，伴随着物种形成脉冲，2）从中期白垩纪（1 亿至 1.1 亿年前）开始，针叶树的灭绝显著增加，此后一直保持在较高水平。被子植物的兴起最能解释它们的灭绝率，从而否定了基于气候变化或时间的替代模型。我们的研究结果支持了一个积极的进化枝替代假说，这意味着与被子植物的直接竞争通过将它们剩余的物种多样性和优势逐出温暖的热带地区，增加了针叶树的灭绝。本研究说明了在气候变化下，整个生命之树上的分支是如何积极竞争生态主导地位的。
