Frequency distributions of VSAs in the parasite population at endemic equilibrium. P. van NoortSander C. NunesMarta D. WeedallGareth HviidLars Gabriela M. GomesM. 2010 <p>Opposing selection pressures favour VSA blocks at each end of the dominance hierarchy (solid red line), suggesting a mechanism behind the two clusters displayed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009778#pone-0009778-g003" target="_blank">Fig. 3</a> of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009778#pone.0009778-Bull4" target="_blank">[35]</a>. Superinfection selects for high-dominance VSAs (compare solid red line and dotted blue line). When parasites contain multiple VSA blocks, acquired immunity selects for low-dominance variants (compare solid red line and dotted green line). Without superinfection and only a single VSA block per parasite, there is no frequency difference between the different VSA blocks (dotted yellow line).</p>