Rapid adaptation to a new carbon source can come at a fitness cost.

<p>A population of glucose-repressed MALS-YeCitrine reference strain (S288c) cells was grown in maltose until 50% of cells had escaped the lag phase and committed to growth on maltose, and then transferred back into glucose-containing media to measure the costs of commitment. Commitment to growth in maltose was measured as the cells' initial expression of the maltase-YeCitrine reporter. These cells were then tracked by time-lapse microscopy to allow growth rate measurements. The blue bars represent cells committed to growth on maltose, which grow at significantly longer doubling times after they were transferred back to glucose compared to sister cells that were still in the lag phase when they were transferred back to glucose (red bars). The results of a Mann–Whitney U test, reported in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001764#pbio.1001764.s010" target="_blank">Figure S2E</a>, show that these differences are robust for MAL “ON” cutoff values greater than background levels (<i>p</i><0.01).