Host alternation of chikungunya virus increases fitness while restricting population diversity and adaptability to novel selective pressures.
Résumé
Mechanisms by which RNA arboviruses including chikungunya virus (CHIKV) evolve and maintain the ability to infect vertebrate and invertebrate hosts are poorly understood. To understand how host specificity shapes arbovirus populations, we studied CHIKV populations passaged between invertebrate↔vertebrate cells to simulate natural alternation, contrasted with populations that were artificially released from cycling by passage in single cell types. These CHIKV populations were characterized by measuring genetic diversity, changes in fitness, and adaptability to novel selective pressures. The greatest fitness increases were observed in alternately passaged CHIKV, without drastic changes in population diversity. The greatest increases in genetic diversity were observed after serial passage and correlated with greater adaptability. These results suggest an evolutionary trade-off between maintaining fitness for invertebrate↔vertebrate cycling, where maximum adaptability is only possible via enhanced population diversity and extensive exploration of sequence space.