Electrophoretic mobility confirms reassortment bias among geographic isolates of segmented RNA phages

Background: Sex presents evolutionary costs and benefits, leading to the expectation that the amount of genetic exchange should vary in conditions with contrasting cost-benefit equations. Like eukaryotes, viruses also engage in sex, but the rate of genetic exchange is often assumed to be a relatively invariant property of a particular virus. However, the rates of genetic exchange can vary within one type of virus according to geography, as highlighted by phylogeographic studies of cystoviruses. Here we merge environmental microbiology with experimental evolution to examine sex in a diverse set of cystoviruses, consisting of the bacteriophage φ6 and its relatives. To quantify reassortment we manipulated – by experimental evolution – electrophoretic mobility of intact virus particles for use as a phenotypic marker to estimate genetic exchange. Results: We generated descendants of φ6 that exhibited fast and slow mobility during gel electrophoresis. We identified mutations associated with s...