Biogeography and diversification rates in hornworts: The limitations of diversification modeling
Biogeography and diversification rates in hornworts: The limitations of diversification modeling
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DOI：
10.12705/642.7
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发表时间：
2015-05
期刊：
影响因子：
3.4
通讯作者：
J. C. Villarreal;N. Cusimano;S. Renner
中科院分区：
文献类型：
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作者：
J. C. Villarreal;N. Cusimano;S. Renner
金鱼草包括ca. 220种，是最古老的陆生植物谱系之一，尽管它们精确的系统发育位置仍不清楚。金鱼藻内部分歧很大，每个属的物种数量极不均匀，以及假定的高茎龄共同表明了多样化变化的历史（即，物种形成减去灭绝）速率。为了研究现代金鱼藻的地理分布及其物种积累模式，我们为代表所有主要群体的103种物种生成了线粒体和质体DNA矩阵，然后应用分子钟测年，使用与早期工作不同的校准方法。我们使用BAMM软件来拟合数据集的速率可变和恒定速率的出生-死亡多样化模型，我们还推断祖先的地区的时间深度为55 Ma（早始新世）。我们分析了多样化率的所有金鱼藻和单独的物种丰富的亚类。在BAMM的可变速率模型下（该模型比恒定速率的出生-死亡模型更适合数据，但仍然假设每个物种无论其年龄如何都具有相同的物种形成和灭绝概率），金鱼藻的物种形成率逐渐增加，背景灭绝率恒定。多样化率没有变化。一个恒定的背景灭绝率的令人难以置信的发现说明了多样化建模的局限性，特别是在灭绝率方面。
Hornworts comprise ca. 220 species and are among the oldest landplant lineages, even though their precise phylogenetic position remains unclear. Deep within-hornwort divergences, highly uneven species numbers per genus, and the assumed high stem age together suggest a history of changing diversification (i.e., speciation minus extinction) rates. To study the geographic distribution of modern hornworts and their patterns of species accumulation, we generated a mitochondrial and plastid DNA matrix for 103 species representing all major groups and then applied molecular-clock dating, using a different calibration approach than in earlier work. We used the BAMM software to fit rate-variable and constant-rate birth-death diversification models to the dataset, and we also inferred ancestral areas to a time depth of 55 Ma (Early Eocene). We analyzed diversification rates for all hornworts and separately for species-rich subclades. Under BAMM’s variable-rates model (which fits the data better than a constant-rate birth-death model, but still assumes that each species has the same speciation and extinction probability regardless of its age), hornworts have gradually increasing rates of speciation and a constant background extinction rate. No shifts in diversification rate could be detected. The implausible finding of a constant background extinction rate illustrates the limitations of diversification modeling especially as regards extinction rates.