@ARTICLE{TreeBASE2Ref18218, author = {Ziheng Yang and Anne D Yoder}, title = {Comparison of Likelihood and Bayesian Methods for Estimating Divergence Times Using Multiple Gene Loci and Calibration Points, with Application to a Radiation of Cute-Looking Mouse Lemur Species.}, year = {2003}, keywords = {}, doi = {10.1080/10635150390235557}, url = {}, pmid = {}, journal = {Systematic Biology}, volume = {52}, number = {5}, pages = {705--716}, abstract = {Divergence time and substitution rate are seriously confounded in phylogenetic analysis, making it difficult to estimate divergence times when the molecular clock (rate constancy among lineages) is violated. This problem can be alleviated to some extent by analyzing multiple gene loci simultaneously and by using multiple calibration points. While different genes may have different patterns of evolutionary rate change, they share the same divergence times. Indeed, the fact that each gene may violate the molecular clock differently leads to the advantage of simultaneous analysis of multiple loci. Multiple calibration points provide the means for characterizing the local evolutionary rates on the phylogeny. In this paper, we extend previous likelihood models of local molecular clock for estimating species divergence times to accommodate multiple calibration points and multiple genes. Heterogeneity among different genes in evolutionary rate and in substitution process is accounted for by the models. We apply the likelihood models to analyze two mitochondrial protein-coding genes, COII and cytochrome b, to estimate divergence times of Malagasy mouse lemurs and related outgroups. The likelihood method is compared with the Bayes method of Thorne et al. (1998), which uses a probabilistic model to describe the change of evolutionary rate over time and uses Markov chain Monte Carlo to derive the posterior distribution of rates and times. Our likelihood implementation has the drawbacks of failing to accommodate uncertainties in fossil calibrations and of requiring the researcher to classify branches on the tree into different rate groups. Both problems are naturally accommodated in the Bayes method. Despite the differences in the two methods, however, we found that data partitions and model assumptions had the greatest impact on date estimation. The three codon positions have very different substitution rates and evolutionary dynamics, and assumptions in the substitution model affect date estimation in both likelihood and Bayes analyses. When the three codon positions are analyzed simultaneously under the most realistic models using all available calibration information, the two methods produced similar results. The divergence of the mouse lemurs is dated to be around 7-10 million years ago, indicating a surprisingly early species radiation for such a morphologically uniform group of primates.} }

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