title: Virus Resistance Is Not Costly in a Marine Alga Evolving under Multiple Environmental Stressors.
abstract: Viruses are important evolutionary drivers of host ecology and evolution. The marine picoplanktonOstreococcus taurihas three known resistance types that arise in response to infection with the Phycodnavirus OtV5: susceptible cells (S) that lyse following viral entry and replication; resistant cells (R) that are refractory to viral entry; and resistant producers (RP) that do not all lyse but maintain some viruses within the population. To test for evolutionary costs of maintaining antiviral resistance, we examined whetherO. tauripopulations composed of each resistance type differed in their evolutionary responses to several environmental drivers (lower light, lower salt, lower phosphate and a changing environment) in the absence of viruses for approximately 200 generations. We did not detect a cost of resistance as measured by life-history traits (population growth rate, cell size and cell chlorophyll content) and competitive ability. Specifically, all R and RP populations remained resistant to OtV5 lysis for the entire 200-generation experiment, whereas lysis occurred in all S populations, suggesting that resistance is not costly to maintain even when direct selection for resistance was removed, or that there could be a genetic constraint preventing return to a susceptible resistance type. Following evolution, all S population densities dropped when inoculated with OtV5, but not to zero, indicating that lysis was incomplete, and that some cells may have gained a resistance mutation over the evolution experiment. These findings suggest that maintaining resistance in the absence of viruses was not costly.
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, The King's Buildings, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK. s.heath-2@sms.ed.ac.uk.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Heath
authors.affiliation: Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, Rutherford Building, Max Born Crescent, Edinburgh EH9 3BF, UK. kirsten.knox@ed.ac.uk.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Knox
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, The King's Buildings, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK. Pedro.Vale@ed.ac.uk.
authors.forename: Pedro F
authors.initials: PF
authors.lastname: Vale
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, The King's Buildings, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK. s.collins@ed.ac.uk.
authors.forename: Sinead
authors.initials: S
authors.lastname: Collins
mesh_terms: D059001:Aquatic Organisms / Q000254:growth & development* / Q000502:physiology / Q000821:virology*; D048429:Cell Size; D002734:Chlorophyll / Q000032:analysis; D000460:Chlorophyta / Q000254:growth & development* / Q000502:physiology / Q000821:virology*; D017862:Phycodnaviridae / Q000254:growth & development*; D013312:Stress, Physiological
chemical_list: D002734:Chlorophyll
keywords: Ostreococcus tauri; Phycodnavirus; Prasinovirus; cost of resistance; environmental change; evolution; marine viral ecology; trade-off; virus-host interactions