Käfer J, de Boer H J, Mousset S, Kool A, Dufay M, Marais G A B
Université Lyon 1, Centre National de la Recherche Scientifique, UMR5558, Laboratoire de Biométrie et Biologie Evolutive, Villeurbanne, France.
J Evol Biol. 2014 Jul;27(7):1478-90. doi: 10.1111/jeb.12385. Epub 2014 May 3.
In angiosperms, dioecious clades tend to have fewer species than their nondioecious sister clades. This departure from the expected equal species richness in the standard sister clade test has been interpreted as implying that dioecious clades diversify less and has initiated a series of studies suggesting that dioecy might be an 'evolutionary dead end'. However, two of us recently showed that the 'equal species richness' null hypothesis is not valid in the case of derived char acters, such as dioecy, and proposed a new test for sister clade comparisons; preliminary results, using a data set available in the litterature, indicated that dioecious clades migth diversify more than expected. However, it is crucial for this new test to distinguish between ancestral and derived cases of dioecy, a criterion that was not taken into account in the available data set. Here, we present a new data set that was obtained by searching the phylogenetic literature on more than 600 completely dioecious angiosperm genera and identifying 115 sister clade pairs for which dioecy is likely to be derived (including > 50% of the dioecious species). Applying the new sister clade test to this new dataset, we confirm the preliminary result that dioecy is associated with an increased diversification rate, a result that does not support the idea that dioecy is an evolutionary dead end in angiosperms. The traits usually associated with dioecy, that is, an arborescent growth form, abiotic pollination, fleshy fruits or a tropical distribution, do not influence the diversification rate. Rather than a low diversification rate, the observed species richness patterns of dioecious clades seem to be better explained by a low transition rate to dioecy and frequent losses.
在被子植物中，雌雄异株的分支往往比其非雌雄异株的姐妹分支物种数量更少。在标准的姐妹分支测试中，这种与预期的物种丰富度相等的偏差被解释为意味着雌雄异株的分支多样化程度较低，并引发了一系列研究，表明雌雄异株可能是一个“进化死胡同”。然而，我们中的两人最近表明，“物种丰富度相等”的零假设在诸如雌雄异株等衍生性状的情况下是无效的，并提出了一种用于姐妹分支比较的新测试；使用文献中可用的数据集得出的初步结果表明，雌雄异株的分支可能比预期的多样化程度更高。然而，对于这项新测试来说，区分雌雄异株的祖先情况和衍生情况至关重要，而现有数据集中并未考虑这一标准。在这里，我们展示了一个新的数据集，该数据集是通过在系统发育文献中搜索600多个完全雌雄异株的被子植物属而获得的，并确定了115对姐妹分支对，其中雌雄异株可能是衍生的（包括超过50%的雌雄异株物种）。将新的姐妹分支测试应用于这个新数据集，我们证实了初步结果，即雌雄异株与多样化速率的增加相关，这一结果不支持雌雄异株是被子植物进化死胡同的观点。通常与雌雄异株相关的性状，即乔木生长形式、非生物授粉、肉质果实或热带分布，不会影响多样化速率。与其说是多样化速率低，雌雄异株分支中观察到的物种丰富度模式似乎更好地由向雌雄异株的低转变速率和频繁丧失来解释。
