ALBERS, MA; BRADLEY, TJ; University of California, Irvine; University of California, Irvine: Osmoregulation in Drosophila melanogaster populations selected for enhanced desiccation resistance

We have examined osmoregulatory ability in the insect Drosophila melanogaster by measuring hemolymph osmotic concentration during desiccation. Hemolymph osmolality was determined using melting point depression measured with a Clifton nanolitre osmometer. We compared the osmoregulatory abilities of flies from five populations which have undergone selection for over 250 generations for enhanced desiccation resistance (D populations) to those of flies from five control populations (C populations). The Ds were measured upon the initiation of a bout of desiccation (time 0) and at 8, 16, 24, and 48h of desiccation. The Cs were measured at 0, 8 and 16h of desiccation. All populations display a high variability in hemolymph osmolality at each measured interval. Hemolymph osmolality increases linearly as a function of the proportional hemolymph dehydration in all C and D populations. Based on the previously quantified average hemolymph volumes of each population, the increase in hemolymph osmotic concentration is significantly lower than what is expected in the absence of osmoregulation (p<0.001 for Cs and Ds). The differences between observed and expected values indicate that both C and D populations osmoregulate during desiccation. The Cs have a greater initial osmolality than the Ds (353.4 � 40.8 and 315 � 28.4, respectively), but the rate of increase during desiccation is not statistically different between the two groups (p>0.1). Supported by NSF grant IBN-0079501