Experimental evolution of the proportion of C. briggsae individuals in competition with C. elegans at different growth temperatures. Two wild strains of C. elegans and C. briggsae from Orsay (A) or Santeuil (B) were competed against each other in the laboratory for several generations at three different temperatures (15°C, 21°C and 27°C). Starting from a frequency of 50% (ten C. elegans L4 larvae and ten C. briggsae L4 larvae), the proportion of C. briggsae individuals was quantified at different time points with five replicate populations per treatment. The mean proportion across replicates is indictaed as a thick line, and error bars indicate standard errors over replicates. Replicates are indicated as thin dotted lines. Time is represented as the number of transfers of each population to a fresh culture plate from the beginning of the experiment. For each treatment, the experiment was continued until all replicates reached fixation of either C. briggsae or C. elegans. With the Santeuil strains at 21°C, C. briggsae outcompeted C. elegans in four out of five replicates.