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Bayesian random local clocks, or one rate to rule them all.

Alexei J Drummond1, Marc A Suchard

  • 1Allan Wilson Centre for Molecular Ecology and Evolution, University of Auckland, Private Bag 92019, Auckland, New Zealand. alexei@cs.auckland.ac.nz

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Summary

This study introduces a new Bayesian method for estimating evolutionary divergence times using random local molecular clocks. This approach effectively models rate variation across lineages, improving phylogenetic inference and providing a direct test against strict molecular clock assumptions.

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Area of Science:

  • Evolutionary biology
  • Computational biology
  • Phylogenetics

Background:

  • Relaxed molecular clock models are crucial for accurate divergence time dating and phylogenetic inference when evolutionary rates vary across lineages.
  • Existing methods often struggle to account for complex rate variations, necessitating more flexible modeling approaches.
  • The assumption of a strict molecular clock, where rates are constant, is frequently violated in real evolutionary data.

Purpose of the Study:

  • To develop and present a novel Bayesian method for phylogenetic inference that relaxes the strict molecular clock assumption.
  • To implement a method that averages over a range of random local molecular clock models, accommodating rate heterogeneity.
  • To provide a direct statistical test for the presence of a strict molecular clock versus models with rate variation.

Main Methods:

  • Utilizes Markov chain Monte Carlo (MCMC) to implement Bayesian model averaging over random local molecular clocks.
  • Proposes a series of local clocks, each applicable to subregions of the phylogeny, allowing for rate changes across branches.
  • The method simultaneously estimates the phylogeny and samples the model space, exploring up to 2(2n-2) possible rate models.

Main Results:

  • An efficient method is presented for sampling the complex model space and estimating phylogenies concurrently.
  • The developed approach allows for a direct comparison between a strict molecular clock and various local molecular clock models.
  • Demonstrated utility on empirical datasets from mammal, primate, and influenza evolution, with exploration of visualization techniques for posterior distributions.

Conclusions:

  • Large sequence datasets can often be adequately modeled using a limited number of local molecular clocks to reconcile branch lengths with evolutionary time.
  • The presented method is implemented in the open-access software package BEAST 1.5.4.
  • The findings suggest that incorporating local molecular clocks improves the accuracy of evolutionary timescale estimations.