Acetic acid resistance of flies with third chromosomes from either Austria or Cameroon in the Cameroon genetic background. Methods and stocks were the same as used for the ethanol resistance assays (see Fig. 5), with 125 μl of 40% glacial acetic acid added to the vials in place of ethanol. Experiment 1: region, P<0.0001; sex, P=0.17; interaction, P>0.8. Experiment 2: region, P<0.0001; sex, P>0.9; interaction, P=0.006 (region effect remained significant when sexes were analyzed separately: females, P<0.001; males, P=0.01).