This study used the Bayesian relaxed clock method to look at the evolutionary history of vertebrate poxviruses that have a AT-rich genome. In order to provide estimates for divergence, this technique is based on a probablishtic moel of the change in evolutionary rates.
Before this study, the authors did a study on the molecular evolution rates of a different group of poxviridae Orthopoxvirus and concluded that the rate of mutation accumulation in the genome was 1.7-4.8 x 10-6 nucleotide substitutions per site per year. This number is considerably lower than the rate of genomes for RNA virses, but it is 2 orders of magnitude higher than the molecular evolution of their host.
The use of molecular dating of viruses is still being verified and validated, particularly with DNA viruses that have an extended genome. These viruses generally have a lower rate of mutation accumulation in their genomes. The Bayesian relaxed clock is generally accepted because it takes into account an inconstant evolutionary rate.
The methodology also considers historical data, such as in this case the genetic relation between two virus strains from West Africa and South American which independently evolved from a common ancestor for a known time period.
When performing evolutionary analysis, highly conserved genes that are a result of stabilizing selection allow a high reliability. Also, it is good to select the geomic loci with a low probability of recombination events.
The results were that the rate of accumulation of nucleotide substitutions is estimated at 0.5-7 x 10-6 nucleotide substitutions per site per year. This meant that Avipoxvirus is estimated to have diverged from the ancestor 249 + or – 69 Tya.
-Lauren Platt
Source: Babkin, I. V. and Babkina, I. N. Molecular Dating in the Evolution of Vertebrate Poxviruses. Intervirology. 2011. 2-8. DOI: 10.1159/000320964
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