Evans Ben J, Kelley Darcy B, Tinsley Richard C, Melnick Don J, Cannatella David C
Department of Biology, McMaster University, Life Sciences Building, Room 328, 1280 Main Street West, Hamilton, Ont., Canada.
Mol Phylogenet Evol. 2004 Oct;33(1):197-213. doi: 10.1016/j.ympev.2004.04.018.
The African clawed frogs (Silurana and Xenopus), model organisms for scientific inquiry, are unusual in that allopolyploidization has occurred on multiple occasions, giving rise to tetraploid, octoploid, and dodecaploid species. To better understand their evolution, here we estimate a mitochondrial DNA phylogeny from all described and some undescribed species. We examine the timing and location of diversification, and test hypotheses concerning the frequency of polyploid speciation and taxonomy. Using a relaxed molecular clock, we estimate that extant clawed frog lineages originated well after the breakup of Gondwana, about 63.7 million years ago, with a 95% confidence interval from 50.4 to 81.3 million years ago. Silurana and two major lineages of Xenopus have overlapping distributions in sub-Saharan Africa, and dispersal-vicariance analysis suggests that clawed frogs originated in central and/or eastern equatorial Africa. Most or all extant species originated before the Pleistocene; recent rainforest refugia probably acted as "lifeboats" that preserved existing species, rather than "species pumps" where many new successful lineages originated. We estimate that polyploidization occurred at least six times in clawed frogs.
非洲爪蟾（滑爪蟾属和爪蟾属）作为科学研究的模式生物，其不同寻常之处在于多次发生了异源多倍体化，产生了四倍体、八倍体和十二倍体物种。为了更好地理解它们的进化过程，我们在此根据所有已描述及部分未描述的物种估算了线粒体DNA系统发育关系。我们研究了物种分化的时间和地点，并检验了有关多倍体物种形成频率和分类学的假设。使用宽松分子钟，我们估计现存爪蟾谱系起源于冈瓦纳大陆分裂之后很久，约6370万年前，95%置信区间为5040万至8130万年前。滑爪蟾属和爪蟾属的两个主要谱系在撒哈拉以南非洲地区分布重叠，扩散-隔离分析表明爪蟾起源于赤道非洲的中部和/或东部。大多数或所有现存物种起源于更新世之前；近期的雨林避难所可能起到了“救生艇”的作用，保护了现有物种，而非许多新的成功谱系起源的“物种泵”。我们估计爪蟾中多倍体化至少发生了六次。
