Experimental evidence indicating that mastreviruses probably did not co-diverge with their hosts

South African National Bioinformatics Institute, University of the Western Cape, Cape Town, South Africa.
Virology Journal (Impact Factor: 2.18). 02/2009; 6(1):104. DOI: 10.1186/1743-422X-6-104
Source: PubMed


Despite the demonstration that geminiviruses, like many other single stranded DNA viruses, are evolving at rates similar to those of RNA viruses, a recent study has suggested that grass-infecting species in the genus Mastrevirus may have co-diverged with their hosts over millions of years. This "co-divergence hypothesis" requires that long-term mastrevirus substitution rates be at least 100,000-fold lower than their basal mutation rates and 10,000-fold lower than their observable short-term substitution rates. The credibility of this hypothesis, therefore, hinges on the testable claim that negative selection during mastrevirus evolution is so potent that it effectively purges 99.999% of all mutations that occur.
We have conducted long-term evolution experiments lasting between 6 and 32 years, where we have determined substitution rates of between 2 and 3 x 10(-4) substitutions/site/year for the mastreviruses Maize streak virus (MSV) and Sugarcane streak Réunion virus (SSRV). We further show that mutation biases are similar for different geminivirus genera, suggesting that mutational processes that drive high basal mutation rates are conserved across the family. Rather than displaying signs of extremely severe negative selection as implied by the co-divergence hypothesis, our evolution experiments indicate that MSV and SSRV are predominantly evolving under neutral genetic drift.
The absence of strong negative selection signals within our evolution experiments and the uniformly high geminivirus substitution rates that we and others have reported suggest that mastreviruses cannot have co-diverged with their hosts.

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    • "Bernard 1994; Pavesi 2005; Gibbs et al. 2010; Torres-P erez et al. 2011). However, for fast evolving viruses, such as those with RNA or small, single-stranded (ss) DNA genomes, the temporal scales of host and virus evolution may be broadly different (Duffy & Holmes 2008; Holmes 2009; Lefeuvre et al. 2011), and codivergence has most often not been observed, or reported examples have been challenged (Harkins et al. 2009; Holmes 2009). Importantly , most studies have focused on demonstrating codivergence at an interspecific rather than at the interpopulation level and mainly neglect which ecological factors drive this process (Paterson & Piertney 2011; but see Torres-P erez et al. 2011). "
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