Figure 4.

Genome streamlining reduces extinction time and hampers TE proliferation. (a) For a single simulation from figure 3, the effects of genome streamlining on lineage viability are illustrated. Before genome streamlining, infected lineages produced more TEs until they went extinct. The x-axis shows the generation number, and the y-axis the number of TEs (for each extinct lineage during this time interval). The left-hand side shows lineages of cells before streamlining evolved (in blue), and the right-hand side after streamlining has evolved (in green). Two arbitrary lineages are highlighted with a thick line for illustrative purposes. (b) For the same simulation as presented in (a), histograms are drawn to visualize changes in extinction time (number of generations since infection) and the number of TEs produced by extinct lineages, before and after streamlining. Blue bars are all lineages that went extinct before time point 20 000, whereas green bars are lineages that went extinct between time points 60 000 and 80 000. Each bin represents the total number of occurrences within that time window. Note that the y-axes are square-root transformed to clearly illustrate the difference between the two distributions. (c) Cartoon illustrating how cells containing streamlined genomes (green), despite spawning fewer progeny in the short term when infected by the same number of TEs, eventually replace cells containing non-streamlined genomes (blue) by limiting opportunities for TE proliferation. Although streamlined genomes may be infected by TEs derived from non-streamlined genomes, newly acquired TEs have little opportunity to amplify because infection of a cell with a streamlined genome is invariably lethal.