Schenk John J, Jacobs Sarah, Hufford Larry
Department of Environmental and Plant Biology, Ohio University, Athens, 45701, Ohio, USA.
Department of Botany, California Academy of Sciences, San Francisco, 94118, California, USA.
Am J Bot. 2025 Jan;112(1):e16455. doi: 10.1002/ajb2.16455. Epub 2025 Jan 11.
The movement of lineages into novel areas can promote ecological opportunity and adaptive radiation, leading to significant species diversity. Not all studies, however, have identified support for ecological opportunity associated with novel intercontinental colonizations. To gain key insights into the drivers of ecological opportunity, we tested whether intercontinental dispersals resulted in ecological opportunity using the Hydrangeaceae-Loasaceae clade, which has numerous centers of diversity across the globe.
A time-calibrated phylogeny was reconstructed from four molecular markers. We tested for bursts of speciation rates followed by a decrease as expected phylogenetic patterns under an ecological opportunity model. Ancestral ranges were estimated using historical biogeographic analyses to examine the relationships of ancestral distributions and habitats with speciation and extinction rates.
Hydrangeaceae and Loasaceae originated in arid Mesoamerica, then dispersed into South America, Eurasia, and eastern North America. Six clades experienced increased diversification rates, but those increases were not associated with transitions into new continental areas. Mentzelia section Bartonia was the only clade that exhibited a burst of speciation followed by a decrease. Both families originated in arid environments and experienced multiple transitions into mesic and tropical environments, but Loasaceae experienced a higher speciation-to-extinction ratio than Hydrangeaceae in the western Nearctic.
Dispersal between continents did not trigger speciation rate shifts in Loasaceae and Hydrangeaceae. Instead, shifts occurred in regions inhabited by intrafamilial relatives and were likely driven by climate change in the Miocene, where species in drier microhabitats diversified into newly created habitats.
谱系向新区域的迁移可以促进生态机遇和适应性辐射，从而带来显著的物种多样性。然而，并非所有研究都证实了与跨大陆新殖民化相关的生态机遇。为了深入了解生态机遇的驱动因素，我们以全球有众多多样性中心的绣球花科-刺莲花科分支为研究对象，测试了跨大陆扩散是否带来了生态机遇。
利用四个分子标记重建了一个时间校准的系统发育树。我们根据生态机遇模型，测试了物种形成速率的爆发，以及随后如预期系统发育模式那样的下降。利用历史生物地理学分析估计祖先分布区，以研究祖先分布和栖息地与物种形成和灭绝速率之间的关系。
绣球花科和刺莲花科起源于干旱的中美洲，然后扩散到南美洲、欧亚大陆和北美东部。六个分支的多样化速率有所增加，但这些增加与向新大陆区域的转变无关。巴特onia门采利菊属是唯一显示出物种形成爆发随后下降的分支。两个科都起源于干旱环境，并经历了多次向湿润和热带环境的转变，但在近北极西部，刺莲花科的物种形成与灭绝比率高于绣球花科。
跨大陆扩散并未引发刺莲花科和绣球花科物种形成速率的变化。相反，变化发生在家族内亲缘物种所栖息的区域，可能是由中新世的气候变化驱动的，在那里，较干燥微生境中的物种在新形成的栖息地实现了多样化。
