Inducible Mutability and Components of Adaptation Figure 2. Average relative fitness indicates adaptive specificity in evolved lineages of P. cichorii 302959. Relative fitness of UVR lineage population samples, UVR lineage isolates, and non-UVR lineage isolates was measured by direct competition with the ancestor under non-UVR (open bars) and UVR (shaded bars) conditions after (A) 250 and (B) 500 generations of experimental evolution. Fitness values are means and error bars represent standard error of the mean. n = 8 for UVR lineage population samples and non-UVR lineage isolates but n = 16 for UVR lineage isolates. Values are significant by two-tailed independent t-test (a = 0.05) where indicated (* P,0.05, ** P,0.01, *** P,0.001). P-paired values correspond to two-tailed paired t-tests (a = 0.05) between average relative fitness values under the two conditions. doi:10.1371/journal.pone.0015975.g002 tions (Figure 2A). Likewise, single-colony isolates from these UVR lineage communities exhibited increased relative fitness at generation 250 in favor of the UVR conditions (Figure 2A). Similar adaptive specificity was observable in population samples and isolates from UVR lineages at generation 500 (all P,0.0013, Figure 2B). The specific differences in relative fitness exhibited by UVR lineages under the two conditions were significant at both generations 250 and 500. Conversely, isolates from non-UVR lineages generally displayed comparable fitness gains under both non-UVR and UVR conditions (Figure 2A). The average relative fitness of population samples and isolates from all lineages at generation 500 was increased under UVR conditions compared to generation 250 (Figure 2B). Population samples taken from individual UVR lineages at generation 250, with the exception of lineage 28, displayed a 15% average improvement in relative fitness under non-UVR condi- tions (all P,0.026, Figure 3A). Under UVR conditions, individual population samples from UVR lineages at generation 250 exhibited a 61% average improvement in relative fitness (all P,0.002, Figure 3B). Only population samples from lineages 28 and 32 exhibited significant differences in relative fitness under non-UVR conditions between generations 250 and 500 (all P,0.017, Figure 3A). However, relative fitness under UVR conditions exhibited by population samples from half of the UVR lineages differed significantly between generations 250 and 500 (all P,0.002, Figure 3B). As described previously, the ancestral P. cichorii 302959 displayed a ‘round’ colony morphology that gave rise to complex mixtures of R and F morphotypes during the experimental evolution of all UVR lineages [12]. Under non-UVR conditions, individual R morphotype isolates recovered at generation 250 from only three UVR lineages (25, 26, and 27) exhibited improvements in relative fitness (all P,0.039, Figure 4A). However, all R isolates from UVR lineages at generation 250 gained relative fitness under UVR conditions by an average of 30% (all P,0.021, Figure 4B). Only an R morphotype isolated from lineage 28 at generation 250 displayed reduced fitness under non-UVR conditions (P = 0.004, Figure 4A). When compared to isolates taken at generation 500, only the relative fitness of R morphotype isolates from UVR lineages 30 and 32 differed significantly under non-UVR conditions (all P,0.02, Figure 4A). Under UVR conditions, the relative fitness of R morphotypes isolated from lineages 30, 31, and 32 differed significantly between generations 250 and 500 (all P,0.040, Figure 4B). Nearly all F morphotypes isolated from UVR lineages at generation 250 exhibited increased fitness under non-UVR conditions by an average of 17% (all P,0.010, Figure 5A). Only an F morphotype isolated from lineage 27 at generation 250 exhibited reduced fitness under non-UVR conditions (P = 0.00005, Figure 5A). Under UVR conditions, all F isolates from UVR lineages at generation 250 gained relative fitness by an average of 35% (all P,0.005, Figure 5B). When compared to isolates taken at generation 500, the relative fitness of F morphotype isolates from UVR lineages 27, 28, 29 and 30 all differed significantly under non-UVR conditions (all P,0.025, Figure 5A). Under UVR conditions, the relative fitness of F morphotypes isolated from lineages 27, 28, and 30 differed significantly between generations 250 and 500 (all P,0.043, Figure 5B). Non-UVR lineages 33–40 contained only R morphotypes. Single-colony isolates from generation 250 displayed a 24% average improvement in relative fitness under non-UVR condi- PLoS ONE | www.plosone.org 4 January 2011 | Volume 6 | Issue 1 | e15975