PREMISE Large disjunctions in species distributions provide excellent opportunities to study processes that shape biogeographic patterns. One such disjunction is the eastern Asia-eastern North America (EA-ENA) floristic disjunction. For many genera with this disjunction, species richness is greater in EA than in ENA; this pattern has been attributed, in part, to higher rates of molecular evolution and speciation in EA. Longer branch lengths have been found in some EA clades, relative to their ENA sister clades, suggesting that the EA lineages have evolved at a higher rate, possibly due to environmental heterogeneity, potentially contributing to the species richness anomaly. METHODS To evaluate whether rates of molecular evolution are elevated in EA relative to ENA, we used transcriptomes from species in 11 genera displaying this disjunction. Rates of molecular evolution were estimated for up to 385 orthologous nuclear loci per genus. RESULTS No statistically significant differences were identified in pairwise comparisons between EA and ENA sister species, suggesting equal rates of molecular evolution for both species; the data also suggest similar selection pressures in both regions. For larger genera, evidence likewise argues against more species-rich clades having higher molecular evolutionary rates, regardless of region. Our results suggest that genes across multiple gene ontology categories are evolving at similar rates under purifying selection in species in both regions. CONCLUSIONS Our data support the hypothesis that greater species richness in EA than ENA is due to factors other than an overall increase in rates of molecular evolution in EA.

中文翻译：

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东亚-北美东部植物区系分离对属进化的遗传洞察：转录组学分析

前提 物种分布的巨大差异为研究塑造生物地理模式的过程提供了极好的机会。一种这样的分离是东亚-北美东部 (EA-ENA) 植物区系分离。对于许多具有这种分离的属，EA 中的物种丰富度高于 ENA；这种模式部分归因于 EA 中分子进化和物种形成的更高速率。相对于它们的 ENA 姐妹进化枝，在一些 EA 进化枝中发现了更长的分支长度，这表明 EA 谱系以更高的速度进化，可能是由于环境异质性，可能导致物种丰富度异常。方法 为了评估 EA 中分子进化的速率是否相对于 ENA 升高，我们使用了来自 11 个属的物种的转录组，显示了这种分离。估计每个属多达 385 个直系同源核位点的分子进化速率。结果 在 EA 和 ENA 姐妹物种之间的成对比较中没有发现统计学上的显着差异，这表明两个物种的分子进化速率相同；数据还表明，这两个区域的选择压力相似。对于更大的属，证据同样反对更多物种丰富的进化枝具有更高的分子进化率，而不管区域如何。我们的结果表明，在两个地区的物种净化选择下，​​跨多个基因本体类别的基因以相似的速度进化。结论 我们的数据支持这样一个假设，即 EA 中物种丰富度高于 ENA 是由于 EA 中分子进化速率总体增加以外的其他因素。