Pleistocene diversification in an ancient lineage: a role for glacial cycles in the evolutionary history of Dioon Lindl. (Zamiaceae).

Premise of the study: Recent estimates of crown ages for cycad genera (Late Miocene) challenge us to consider what processes have produced the extant diversity of this ancient group in such relatively little time. Pleistocene climate change has driven major shifts in species distributions in Mexico and may have led to speciation in the genus Dioon by forcing populations to migrate up in elevation thereby becoming separated by topography. Methods: We inferred orthologs from transcriptomes of five species and sequenced these in 42 individuals representing all Dioon species. From these data and published plastid sequences we inferred dated species trees and lineage-specific diversification rates. Key results: 84 nuclear orthologs and plastid data confirm four major clades within Dioon, all of Pleistocene age. Gene tree analysis, divergence dates, and an increase in diversification rate support very recent and rapid divergence of extant taxa. Conclusions: This study confirms the Pleistoc...研究背景：近期针对各苏铁属冠群年龄的估算结果（晚中新世时期）促使我们思考，这一古老类群的现存多样性为何能在如此短的相对时间内形成。更新世气候变化驱动了墨西哥境内物种分布的重大变迁，可能通过迫使种群向高海拔区域迁移、进而被地形分隔开来，促成了苏铁属（Dioon）的物种形成。 方法：我们从5个物种的转录组（transcriptomes）中推断得到直系同源基因（orthologs），并在涵盖所有苏铁属物种的42个个体中对这些基因进行了测序。结合上述数据与已发表的质体（plastid）序列，我们构建了定年物种树（dated species trees）并分析了支系特异性的多样化速率（diversification rates）。 关键结果：84个核直系同源基因与质体数据证实，苏铁属内存在4个主要演化支（clades），所有演化支的分化时间均处于更新世时期。基因树分析、分化时间估算以及多样化速率上升的结果，均支持现存类群发生了极晚近且快速的分化。 结论：本研究证实了更新世……