Meeting Abstract
P1.17 Monday, Jan. 4 The significance of energetic constraints on the evolution of inducible physiologies HOEKSTRA, L.A.**; MONTOOTH, K.L.; Indiana University, Bloomington lhoekstr@indiana.edu
One solution to unpredictable thermal stress is the evolution of an inducible stress response; often involving the massive upregulation of molecular chaperones when temperature exceeds a sublethal threshold. Fueling this massive expression of stress response genes and the translation of stress response proteins should increase short term energetic costs, but the evolution of inducibility is thought to be favored in environments where the benefits of constitutive expression are unpredictable. We will present data that addresses the following questions: Are there evident energetic costs to inducible physiological responses? Can we quantify the significance of energetic constraints in terms of metabolic rate and fitness? To quantify energetic costs we used lines of Drosophila melanogaster that differ in Hsp70 gene copy number and differ by as much as ten fold in the inducibility of Hsp70 mRNA expression (Bettencourt et al., 2008, BMC Biology, 6:5). Using flow-through respirometry, we measured the metabolic performance of larvae with different Hsp70 copy numbers before, during, and after induction of the heat shock response. We show that whole organism energy expenditure during induction of the heat shock response varies with Hsp70 copy number and that larvae with more copies of Hsp70 take longer to return to their resting metabolic state. Next, we examined the significance of energetic constraints in terms of fitness using lines of Drosophila melanogaster deficient in components of the oxidative phosphorylation pathway. If energy is limiting during the physiologically demanding heat shock response, then metabolically compromised larvae should differ either in heat shock survival or metabolic rate. Together these results provide valuable information about the metabolic cost of gene expression and the evolution of threshold traits.
