Polyploid formation shapes flowering plant diversity

Polyploidy, or whole genome duplication, has been an important feature of eukaryotic evolution. This is especially true in flowering plants, where all extant angiosperms have descended from polyploid species. Here we present a broad comparative analysis of the effect of polyploidy on flowering plant diversity. We examine the widely held hypothesis that polyploid flowering plants generate more diversity than their diploid counterparts, by fitting stochastic birth/death models to observed ploidal frequency data from 60 extant angiosperm genera. Our results suggest the opposite, that diploids speciate at higher rates than polyploids, through a combination of simple diploid speciation and tetraploidy. Importantly, the estimated diploid advantage stemmed primarily from a higher rate of polyploidization in diploids than polyploids. Our model is also able to account for the empirically observed correlation between polyploidy and species richness without assuming that polyploids have a speciation advantage over diploids.

多倍体化（Polyploidy），又称全基因组复制（whole genome duplication），是真核生物演化的重要特征之一。这一特征在被子植物（flowering plants）中尤为显著，所有现存的被子植物（angiosperms）均由多倍体物种演化而来。本研究针对多倍体化对被子植物多样性的影响开展了一项大规模比较分析。我们通过将随机出生-死亡模型（stochastic birth/death models）拟合至60个现存被子植物属的倍性频率观测数据，对学界广为认可的假说——多倍体被子植物相较于其二倍体同类可产生更多物种多样性——进行了检验。研究结果却得出了相反的结论：二倍体的物种形成速率高于多倍体，这一现象源于单纯二倍体物种形成与四倍体化的共同作用。值得注意的是，估算得到的二倍体优势主要源于二倍体相较于多倍体更高的多倍体化速率。此外，本模型无需假设多倍体相较于二倍体具有物种形成优势，即可解释实证观测到的多倍体化与物种丰富度之间的相关性。