Abiotic adaptation of bacterial populations
Growth performance of bacterial populations from the end of the evolution experiment was measured in the absence of phages, without immigration (Figure 3). The bacteria evolution lines (B) showed the most pronounced increase in growth performance compared with the ancestral strain (one-tailed t -test: t 5 = 17.831,P < 0.001), followed by bacterial lines with immigration (B+IB) (one-tailed t -test: t 5= 8.120, P < 0.001). Growth performance of bacteria from bacteria/phage lines (BP) was not different from the ancestral strain (one-tailed t -test: t 5 = 0.681,P = 0.737). Bacteria from bacteria/phage lines with phage immigration (BP+IP) showed the poorest growth performance, significantly lower than that of the ancestral strain (one-tailed Wilcoxon test:V = 2, P = 0.047); and those from bacteria/phage lines with bacteria/phage immigration (BP+IBP) did not significantly differ from the ancestral strain (one-tailed t -test:t 4 = -0.605, P = 0.290).
Comparisons between evolution lines were also carried out (Figure 3). Immigration of bacteria from 28°C habitats reduced the extent of abiotic adaptation (B versus B+IB treatment, one-tailed Welch two-samplet -test: t 9.682 = 5.169, P< 0.001). The presence of phages limited bacterial abiotic adaptation (B versus BP, one-tailed Welch two-sample t -test:t 5.500 = 3.230, P = 0.010); and immigration of phages only further reduced bacterial abiotic adaptation (BP versus BP+IP, one-tailed Welch two-sample t -test:t 9.599 = 1.924, P = 0.042), though joint bacteria and phage immigration did not significantly alter bacterial abiotic adaptation (BP versus BP+IBP, one-tailed Welch two-samplet -test: t 7.732 = 0.891, P = 0.200).