Department of Science and Education, The Field Museum, Integrative Research Center, Chicago, IL, USA.
Committee on Evolutionary Biology, University of Chicago, Chicago, IL, USA.
Geobiology. 2020 Jan;18(1):3-13. doi: 10.1111/gbi.12369. Epub 2019 Nov 14.
The early-successional status of lichens in modern terrestrial ecosystems, together with the role lichen-mediated weathering plays in the carbon cycle, have contributed to the long and widely held assumption that lichens occupied early terrestrial ecosystems prior to the evolution of vascular plants and drove global change during this time. Their poor preservation potential and the classification of ambiguous fossils as lichens or other fungal-algal associations have further reinforced this view. As unambiguous fossil data are lacking to demonstrate the presence of lichens prior to vascular plants, we utilize an alternate approach to assess their historic presence in early terrestrial ecosystems. Here, we analyze new time-calibrated phylogenies of ascomycete fungi and chlorophytan algae, that intensively sample lineages with lichen symbionts. Age estimates for several interacting clades show broad congruence and demonstrate that fungal origins of lichenization postdate the earliest tracheophytes. Coupled with the absence of unambiguous fossil data, our work finds no support for lichens having mediated global change during the Neoproterozoic-early Paleozoic prior to vascular plants. We conclude by discussing our findings in the context of Neoproterozoic-Paleozoic terrestrial ecosystem evolution and the paleoecological context in which vascular plants evolved.
地衣在现代陆地生态系统中的早期演替地位，以及地衣介导的风化作用在碳循环中所起的作用，使得人们长期以来一直认为地衣在维管植物进化之前就占据了早期陆地生态系统，并在这一时期推动了全球变化。它们保存潜力差，以及将模糊化石分类为地衣或其他真菌-藻类共生体，进一步强化了这一观点。由于缺乏明确的化石数据来证明地衣在维管植物之前存在，我们采用替代方法来评估它们在早期陆地生态系统中的历史存在。在这里，我们分析了子囊菌真菌和绿藻的新的时间校准系统发育，这些系统发育密集地采样了具有地衣共生体的谱系。几个相互作用的进化枝的年龄估计显示出广泛的一致性，并表明地衣化的真菌起源晚于最早的维管植物。结合缺乏明确的化石数据，我们的工作发现，在地衣植物之前的新元古代-早古生代，地衣并没有在全球变化中发挥作用。最后，我们在讨论新元古代-古生代陆地生态系统进化以及维管植物进化的古生态学背景的背景下讨论了我们的发现。
