最古老现存维管植物属石松（木贼科）的生物地理学和基因组大小演化。
Biogeography and genome size evolution of the oldest extant vascular plant genus, Equisetum (Equisetaceae).
机构信息
Royal Botanic Gardens, Kew, Richmond, UK.
Department of Environment and Agriculture, Curtin University, Perth, WA, Australia.
出版信息
Ann Bot. 2021 Apr 17;127(5):681-695. doi: 10.1093/aob/mcab005.
BACKGROUND AND AIMS
Extant plant groups with a long fossil history are key elements in understanding vascular plant evolution. Horsetails (Equisetum, Equisetaceae) have a nearly continuous fossil record dating back to the Carboniferous, but their phylogenetic and biogeographic patterns are still poorly understood. We use here the most extensive phylogenetic analysis to date as a framework to evaluate their age, biogeography and genome size evolution.
METHODS
DNA sequences of four plastid loci were used to estimate divergence times and investigate the biogeographic history of all extant species of Equisetum. Flow cytometry was used to study genome size evolution against the framework of phylogenetic relationships in Equisetum.
KEY RESULTS
On a well-supported phylogenetic tree including all extant Equisetum species, a molecular clock calibrated with multiple fossils places the node at which the outgroup and Equisetum diverged at 343 Mya (Early Carboniferous), with the first major split among extant species occurring 170 Mya (Middle Jurassic). These dates are older than those reported in some other recent molecular clock studies but are largely in agreement with a timeline established by fossil appearance in the geological record. Representatives of evergreen subgenus Hippochaete have much larger genome sizes than those of deciduous subgenus Equisetum, despite their shared conserved chromosome number. Subgenus Paramochaete has an intermediate genome size and maintains the same number of chromosomes.
CONCLUSIONS
The first divergences among extant members of the genus coincided with the break-up of Pangaea and the resulting more humid, warmer climate. Subsequent tectonic activity most likely involved vicariance events that led to species divergences combined with some more recent, long-distance dispersal events. We hypothesize that differences in genome size between subgenera may be related to the number of sperm flagellae.
背景与目的
具有悠久化石历史的现存植物群是理解维管植物进化的关键因素。木贼（木贼属，木贼科）的化石记录几乎可以追溯到石炭纪，但它们的系统发育和生物地理学模式仍知之甚少。在这里，我们使用迄今为止最广泛的系统发育分析作为框架，评估它们的年龄、生物地理学和基因组大小演化。
方法
使用四个质体基因座的 DNA 序列来估计分歧时间，并研究所有现存木贼属植物的生物地理学历史。利用流式细胞术，在木贼属的系统发育关系框架内研究基因组大小的演化。
主要结果
在一个包含所有现存木贼属物种的高度支持的系统发育树上，一个用多个化石校准的分子钟将外群和木贼属分化的节点置于 3.43 亿年前（早石炭纪），现存物种的第一次主要分化发生在 1.7 亿年前（中侏罗纪）。这些日期比一些最近的分子钟研究报告的日期要老，但与地质记录中化石出现所建立的时间线基本一致。尽管常绿亚属 Hippochaete 的代表具有比落叶亚属 Equisetum 更大的基因组大小，但它们具有相同的染色体数目。中间亚属 Paramochaete 的基因组大小居中，并保持相同的染色体数目。
结论
现存属成员的第一次分化与泛大陆的分裂以及由此产生的更潮湿、更温暖的气候同时发生。随后的构造活动很可能涉及到导致物种分化的隔离事件，再加上一些最近的长距离扩散事件。我们假设亚属之间的基因组大小差异可能与精子鞭毛的数量有关。
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