Evolution of ammonia and urea tolerance in Drosophila melanogaster: resistance and cross-tolerance

We examined whether populations of Drosophila melanogaster could evolve a g enetically based tolerance to high levels of toxic compounds (urea or ammon ia) added to their larval food medium. We also examined whether tolerance t o one compound may impart cross-tolerance to other compounds. Five populati ons selected for ammonia tolerance (AX), five populations selected for urea tolerance (UX), and five unselected controls (AUC) were assayed for develo pmental time, viability, and female fertility. These characteristics were m easured on each of the 15 populations reared on one of three larval food co nditions (plain banana-molasses, 0.35 M NH4Cl, or 0.266 M urea). On urea-su pplemented media, the urea-selected populations developed fastest and expre ssed the highest viability; the ammonia-selected populations developed sign ificantly faster and had a higher viability than the controls. Similarly, o n ammonia-supplemented media, the ammonia-selected populations developed fa stest and expressed the highest viability; the urea-selected populations de veloped significantly faster and had a higher viability than the controls. This suggests that a cross-tolerance exists for resisting different toxic c ompounds. Urea-selected females reared on urea-containing food media displa yed superior fecundity, without any observable cross-tolerance effect. When all populations were reared on food containing 0.266 M urea, the urea-sele cted populations had the lowest levels of urea in their tissues. All popula tions reared on food containing 0.37 M ammonia or 0.266 M urea, contained m ore ammonia in their tissues than did populations reared on plain food. (C) 2000 Elsevier Science Ltd. All rights reserved.