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Figure 8 | BMC Genomics

Figure 8

From: Inter- and intra-specific pan-genomes of Borrelia burgdorferi sensu lato: genome stability and adaptive radiation

Figure 8

Predicted increase of genomic diversity with B. burgdorferi population expansion. We simulated evolution of three bacterial populations, each of which consisted of a constant size of N=500 (in green), 1000 (in blue), or 2000 (in red) haploid genomes. One of the eight genes in the simulated genome evolves under immune-mediated negative frequency-dependent selection (FDS) as ospC is likely to be. Other genes were under purifying selection like housekeeping genes. (A) We measured nucleotide diversity at the FDS locus by sampling 100 individuals every 500 generations. Doubling of the population size results in a proportional increase in nucleotide diversity. (Inset) We reconstructed the coalescence trees for the last population samples. These trees show characteristics of balancing selection such as elongated internal branches and compressed terminal branches. (B) Lineage-Through-Time (LTT) plots of the tree based on ospC sequences from 14 B. burgdorferi s.s. genomes (in black), a simulated neutral coalescence tree (in orange), and trees of FDS sequences from simulated populations (in green, blue, and red). In comparison with the neutrally evolving genomes, the LTT plots of balanced gene trees show early rapid rise of gene lineages that are subsequently maintained for a long period of time, before the final rapid rise to the sample sizes.

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