School of Biology and Environmental Science, University College Dublin, Belfield, Dublin, Ireland.
Systematics Lab, Department of Environmental Studies, University of Delhi, Delhi, India.
Mol Biol Evol. 2017 Mar 1;34(3):744-771. doi: 10.1093/molbev/msw267.
Molecular dating studies typically need fossils to calibrate the analyses. Unfortunately, the fossil record is extremely poor or presently nonexistent for many species groups, rendering such dating analysis difficult. One such group is the Asian horned frogs (Megophryinae). Sampling all generic nomina, we combined a novel ∼5 kb dataset composed of four nuclear and three mitochondrial gene fragments to produce a robust phylogeny, with an extensive external morphological study to produce a working taxonomy for the group. Expanding the molecular dataset to include out-groups of fossil-represented ancestral anuran families, we compared the priorless RelTime dating method with the widely used prior-based Bayesian timetree method, MCMCtree, utilizing a novel combination of fossil priors for anuran phylogenetic dating. The phylogeny was then subjected to ancestral phylogeographic analyses, and dating estimates were compared with likely biogeographic vicariant events. Phylogenetic analyses demonstrated that previously proposed systematic hypotheses were incorrect due to the paraphyly of genera. Molecular phylogenetic, morphological, and timetree results support the recognition of Megophryinae as a single genus, Megophrys, with a subgenus level classification. Timetree results using RelTime better corresponded with the known fossil record for the out-group anuran tree. For the priorless in-group, it also outperformed MCMCtree when node date estimates were compared with likely influential historical biogeographic events, providing novel insights into the evolutionary history of this pan-Asian anuran group. Given a relatively small molecular dataset, and limited prior knowledge, this study demonstrates that the computationally rapid RelTime dating tool may outperform more popular and complex prior reliant timetree methodologies.
分子年代学研究通常需要化石来校准分析。不幸的是，对于许多物种群来说，化石记录极其匮乏或目前不存在，这使得这种年代分析变得困难。亚洲角蛙（Megophryinae）就是这样一个群体。我们对所有的属名进行采样，结合了一个新颖的约 5kb 数据集，由四个核基因片段和三个线粒体基因片段组成，生成了一个稳健的系统发育，同时进行了广泛的外部形态学研究，为该群体生成了一个可行的分类学。将分子数据集扩展到包括具有化石代表的祖先蛙类家族的外群，我们比较了无先验的 RelTime 年代测定方法和广泛使用的基于先验的贝叶斯时间树方法 MCMCtree，利用蛙类系统发育年代测定的新化石先验组合。然后对系统发育进行祖先地理分析，并将年代估计与可能的生物地理隔离事件进行比较。系统发育分析表明，由于属的并系性，以前提出的系统假设是不正确的。分子系统发育、形态和时间树结果支持将 Megophryinae 作为一个单一属，Megophrys，以及亚属水平分类的识别。使用 RelTime 的时间树结果与外群蛙类树的已知化石记录更相符。对于无先验的内群，当节点日期估计与可能有影响力的历史生物地理事件进行比较时，它也优于 MCMCtree，为这个泛亚洲蛙类群体的进化历史提供了新的见解。考虑到相对较小的分子数据集和有限的先验知识，这项研究表明，计算速度较快的 RelTime 年代测定工具可能优于更流行和复杂的基于先验的时间树方法。
