Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0807707105 (2008)

The exceedingly abundant phytoplankton, Emiliania huxleyi, has unusual population dynamics. It can evade viral infection in its haploid form, when it has only one copy of each of its chromosomes, but it is susceptible to the same source of infection during the diploid part of its life cycle, when its cells contain twice as much DNA.

Miguel Frada at the Station Biologique in Roscoff, France, and his colleagues subjected the phytoplankton to giant phycodnaviruses. Unlike the diploid cells, the haploid ones did not burst open — perhaps owing to their uncalcified membranes somehow preventing the virus from entering the cells.