Present address: Biogeosciences, Queensland University of Technology, Brisbane, Qld, Australia.
Time-dependent rates of molecular evolution
Article first published online: 8 JUL 2011
© 2011 Blackwell Publishing Ltd
Volume 20, Issue 15, pages 3087–3101, August 2011
How to Cite
HO, S. Y. W., LANFEAR, R., BROMHAM, L., PHILLIPS, M. J., SOUBRIER, J., RODRIGO, A. G. and COOPER, A. (2011), Time-dependent rates of molecular evolution. Molecular Ecology, 20: 3087–3101. doi: 10.1111/j.1365-294X.2011.05178.x
- Issue published online: 21 JUL 2011
- Article first published online: 8 JUL 2011
- Received 23 February 2011; revision received 24 May 2011; accepted 1 June 2011
- divergence times;
- molecular clock;
- mutation rate;
- purifying selection;
- substitution rate
For over half a century, it has been known that the rate of morphological evolution appears to vary with the time frame of measurement. Rates of microevolutionary change, measured between successive generations, were found to be far higher than rates of macroevolutionary change inferred from the fossil record. More recently, it has been suggested that rates of molecular evolution are also time dependent, with the estimated rate depending on the timescale of measurement. This followed surprising observations that estimates of mutation rates, obtained in studies of pedigrees and laboratory mutation-accumulation lines, exceeded long-term substitution rates by an order of magnitude or more. Although a range of studies have provided evidence for such a pattern, the hypothesis remains relatively contentious. Furthermore, there is ongoing discussion about the factors that can cause molecular rate estimates to be dependent on time. Here we present an overview of our current understanding of time-dependent rates. We provide a summary of the evidence for time-dependent rates in animals, bacteria and viruses. We review the various biological and methodological factors that can cause rates to be time dependent, including the effects of natural selection, calibration errors, model misspecification and other artefacts. We also describe the challenges in calibrating estimates of molecular rates, particularly on the intermediate timescales that are critical for an accurate characterization of time-dependent rates. This has important consequences for the use of molecular-clock methods to estimate timescales of recent evolutionary events.