Université de Lyon; Université Lyon 1; CNRS; UMR 5558; Laboratoire de Biométrie et Biologie Evolutive; F-69622, Villeurbanne, France
Université de Lyon; Université Lyon 1; CNRS; UMR 5558; Laboratoire de Biométrie et Biologie Evolutive; F-69622, Villeurbanne, France.
Syst Biol. 2014 Jul;63(4):601-9. doi: 10.1093/sysbio/syu024. Epub 2014 Mar 26.
Comparing species richness in sister clades that differ in a character state is one of the ways to study factors influencing diversification. While most of its applications have focussed on traits that increase diversification, some have been used to study the association of a trait with lower species richness, e.g., the occurrence of dioecy in flowering plants. We show here, using simulations and an analytical model, that the null expectation of equal species richness that is generally used in sister clade comparisons is wrong in the case of a derived trait occurring independently from speciation: one should expect fewer species in the clade with the derived character state when there is no difference in diversification rates. This is due to the waiting time for the derived state to appear, which causes it to occur more often on longer branches. This has the important implication that the probability for a clade to possess the derived state depends on the tree geometry, and thus on species richness: species-poorer clades are more likely to possess the derived state. We develop a statistical test for sister clade comparisons to study the effect of a derived character state. Applying it to a data set of dioecious clades, we find that we cannot confirm earlier work that concluded that dioecy decreases diversification; on the contrary, it seems to be associated to higher species richness than expected. [angiosperms; dioecy; diversification; sister clades; species richness.].
比较在特征状态上不同的姐妹分支中的物种丰富度是研究影响多样化因素的方法之一。虽然大多数应用都集中在增加多样化的特征上，但有些应用已经用于研究特征与较低物种丰富度的关联，例如，开花植物中的雌雄异株。我们在这里使用模拟和分析模型表明，在衍生特征独立于物种形成出现的情况下，通常用于姐妹分支比较的具有相等物种丰富度的零假设是错误的：在没有多样化率差异的情况下，具有衍生特征状态的分支中应该具有较少的物种。这是由于等待衍生状态出现的时间，这导致它更经常出现在更长的分支上。这具有重要的意义，即一个分支拥有衍生状态的概率取决于树的几何形状，因此取决于物种丰富度：物种较少的分支更有可能拥有衍生状态。我们为姐妹分支比较开发了一个统计检验，以研究衍生特征状态的影响。将其应用于雌雄异株分支的数据集，我们发现我们不能证实早期的工作，该工作得出结论认为雌雄异株会降低多样化；相反，它似乎与比预期更高的物种丰富度有关。[被子植物；雌雄异株；多样化；姐妹分支；物种丰富度。]
