Transient, context‐dependent fitness costs accompanying viral resistance in isolates of the marine microalga Micromonas sp. (class Mamiellophyceae)

• Published in: Environmental microbiology 2024-07, Vol.26 (8), p.e16686-n/a
• Main Authors: Bedi de Silva, Anamica, Polson, Shawn W., Schvarcz, Christopher R., Steward, Grieg F., Edwards, Kyle F.
• Format: Article
• Language: English
• Subjects: Biogeochemical cycles; Cell culture; Chlorophyta - genetics; Chlorophyta - virology; Context; Costs; Disease resistance; DNA Viruses - genetics; Environmental conditions; Evolution; Fitness; Genetic Fitness; Growth rate; Irradiance; Microalgae - genetics; Microalgae - virology; Microbiological strains; Micromonas; Phytoplankton; Plankton; Protists; Reproductive fitness; Strains (organisms); Viruses
• ISSN: 1462-2912; 1462-2920; 1462-2920
• DOI: 10.1111/1462-2920.16686

Marine microbes are important in biogeochemical cycling, but the nature and magnitude of their contributions are influenced by their associated viruses. In the presence of a lytic virus, cells that have evolved resistance to infection have an obvious fitness advantage over relatives that remain susceptible. However, susceptible cells remain extant in the wild, implying that the evolution of a fitness advantage in one dimension (virus resistance) must be accompanied by a fitness cost in another dimension. Identifying costs of resistance is challenging because fitness is context‐dependent. We examined the context dependence of fitness costs in isolates of the picophytoplankton genus Micromonas and their co‐occurring dsDNA viruses using experimental evolution. After generating 88 resistant lineages from two ancestral Micromonas strains, each challenged with one of four distinct viral strains, we found resistance led to a 46% decrease in mean growth rate under high irradiance and a 19% decrease under low. After a year in culture, the experimentally selected lines remained resistant, but fitness costs had attenuated. Our results suggest that the cost of resistance in Micromonas is dependent on environmental conditions and the duration of population adaptation, illustrating the dynamic nature of fitness costs of viral resistance among marine protists. We generated 88 cell lines of the marine alga Micromonas that were resistant to viral lytic infection to investigate how viral resistance can affect fitness, in the form of growth rate, under high and low light laboratory conditions. We conducted growth assays shortly after selection for resistance and again 1 year later in order to determine if time since acquiring resistance affected growth rate. Fitness was significantly affected shortly after isolation under high light conditions.