PIERCE, V.A.*; ELGHANDOUR, R.S.; JARROUGE, E.G.; MARCINKIEWICZ, A.: Using laboratory populations of D. melanogaster to study adaptation of metabolic pathways.

We are systematically investigating competing models of metabolic regulation with respect to temperature acclimation and adaptation. We propose two hypotheses: (1) the enzyme(s) in a pathway that show the greatest thermal sensitivity will be the targets of selection, regardless of the type of reaction catalyzed, and (2) these enzymes may respond to thermal selection by either acclimation or constitutive changes in enzyme activity. We are characterizing the allelic variation, thermal sensitivity and acclimation response of all the enzymes in a single pathway, glycolysis, in the thorax of outbred laboratory populations of the fruitfly Drosophila melanogaster. These data will allow us to predict how many and which enzymes should respond to temperature selection. We will then select these populations for adaptation to different thermal environments and test our predictions. Cellulose acetate electrophoresis indicates that five of ten glycolytic enzymes are monomorphic in our populations and three enzymes have two alleles each. We were unable to genotype hexokinase and enolase. Thus far, the thermal sensitivities of 3 enzymes have been characterized by assaying maximal initial activities at 6 temperatures and fitting an exponential growth equation to the data. Phosphoglucoisomerase, phosphoglyceromutase and phosphoglycerokinase all appear to have similar Q₁₀ ratios of 1.6. PGI and PGM maximal activities do not show any acclimation responses among adult flies held at 19°C, 25°C and 29°C. Thus the enzymes examined so far, despite catalyzing different types of reaction, show similar thermal properties and should show similar responses to temperature selection.