MANY-TRILLIONFOLD AMPLIFICATION OF SINGLE RNA VIRUS-PARTICLES FAILS TO OVERCOME THE MULLER RATCHET EFFECT

We showed earlier that transfers of large populations of RNA viruses l ead to fitness gains and that repeated genetic bottleneck transfers re sult in fitness losses due to Muller's ratchet. In the present study, we examined the effects of genetic bottleneck passages intervening bet ween population passages, a process akin to some natural viral transmi ssions, using vesicular stomatitis virus as a model. Our findings show that the pronounced fitness increases that occur during two successiv e population passages cannot overcome the fitness decreases caused by a single intervening genetic bottleneck passage. The implications for natural transmissions of RNA viruses are discussed.