The influence of rate heterogeneity among sites on the time dependence of molecular rates

Julien Soubrier, Mike Steel, Mike Lee, Clio Der Sarkissian, Stephane Guindon, Simon Ho, Alan Cooper

    Research output: Contribution to journalArticlepeer-review

    132 Citations (Scopus)


    Molecular evolutionary rate estimates have been shown to depend on the time period over which they are estimated. Factors such as demographic processes, calibration errors, purifying selection, and the heterogeneity of substitution rates among sites (RHAS) are known to affect the accuracy with which rates of evolution are estimated. We use mathematical modeling and Bayesian analyses of simulated sequence alignments to explore how mutational hotspots can lead to time-dependent rate estimates. Mathematical modeling shows that underestimation of molecular rates over increasing time scales is inevitable when RHAS is ignored. Although a gamma distribution is commonly used to model RHAS, we show that when the actual RHAS deviates from a gamma-like distribution, rates can either be under-or overestimated in a time-dependent manner. Simulations performed under different scenarios of RHAS confirm the mathematical modeling and demonstrate the impacts of time-dependent rates on estimates of divergence times. Most notably, erroneous rate estimates can have narrow credibility intervals, leading to false confidence in biased estimates of rates, and node ages. Surprisingly, large errors in estimates of overall molecular rate do not necessarily generate large errors in divergence time estimates. Finally, we illustrate the correlation between time-dependent rate patterns and differential saturation between quickly and slowly evolving sites. Our results suggest that data partitioning or simple nonparametric mixture models of RHAS significantly improve the accuracy with which node ages and substitution rates can be estimated.

    Original languageEnglish
    Pages (from-to)3345-3358
    Number of pages14
    Issue number11
    Publication statusPublished - Nov 2012


    • among-site rate variation
    • divergence times
    • molecular clock
    • substitution rate
    • time-dependent rates


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