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Contrasting Rates of Molecular Evolution and Patterns of Selection among Gymnosperms and Flowering Plants

机译：裸子植物和开花植物间分子进化和选择模式的对比速率

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摘要

The majority of variation in rates of molecular evolution among seed plants remains both unexplored and unexplained. Although some attention has been given to flowering plants, reports of molecular evolutionary rates for their sister plant clade (gymnosperms) are scarce, and to our knowledge differences in molecular evolution among seed plant clades have never been tested in a phylogenetic framework. Angiosperms and gymnosperms differ in a number of features, of which contrasting reproductive biology, life spans, and population sizes are the most prominent. The highly conserved morphology of gymnosperms evidenced by similarity of extant species to fossil records and the high levels of macrosynteny at the genomic level have led scientists to believe that gymnosperms are slow-evolving plants, although some studies have offered contradictory results. Here, we used 31,968 nucleotide sites obtained from orthologous genes across a wide taxonomic sampling that includes representatives of most conifers, cycads, ginkgo, and many angiosperms with a sequenced genome. Our results suggest that angiosperms and gymnosperms differ considerably in their rates of molecular evolution per unit time, with gymnosperm rates being, on average, seven times lower than angiosperm species. Longer generation times and larger genome sizes are some of the factors explaining the slow rates of molecular evolution found in gymnosperms. In contrast to their slow rates of molecular evolution, gymnosperms possess higher substitution rate ratios than angiosperm taxa. Finally, our study suggests stronger and more efficient purifying and diversifying selection in gymnosperm than in angiosperm species, probably in relation to larger effective population sizes.
机译：种子植物中分子进化速率的大多数变化仍然是未知的和未知的。尽管已对开花植物给予了一定的关注，但有关其姊妹植物进化枝（裸子植物）的分子进化速率的报道却很少，而且据我们所知，种子植物进化枝之间的分子进化差异从未在系统发育框架中得到检验。被子植物和裸子植物在许多特征上都不同，其中生殖生物学，寿命和种群数量的差异最为明显。裸子植物的形态高度保守，这与现存物种与化石记录的相似性以及基因组水平上的高统合水平所证明，使科学家们认为，裸子植物是进化缓慢的植物，尽管一些研究提供了相互矛盾的结果。在这里，我们使用了从广泛分类学样本中的直系同源基因获得的31,968个核苷酸位点，其中包括大多数针叶树，苏铁，银杏和许多被子植物的序列基因组。我们的结果表明，被子植物和裸子植物每单位时间的分子进化速率差异很大，裸子植物的平均速率比被子植物低7倍。更长的生成时间和更大的基因组大小是解释裸子植物中分子进化速度缓慢的一些因素。与裸子植物的分子进化速度相比，裸子植物具有比被子植物类群更高的替代率比。最后，我们的研究表明，裸子植物比被子植物更有效，更有效地进行纯化和多样化选择，这可能与更大的有效种群数量有关。

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