Life-history correlates of evolution under high and low adult mortality

Life-history theory predicts evolutionary changes in reproductive traits an d intrinsic mortality rates in response to differences in extrinsic mortali ty rates. Trade-offs between life- history traits play a pivotal role in th ese predictions, and such trade-offs are mediated, at least in part, by phy siological allocations. To gain insight into these trade-offs, we have been performing a long-term experiment in which we allow fruitflies, Drosophila melanogaster, to evolve in response to high (HAM) and low (LAM) adult mort ality rates. Hen we analyze the physiological correlates of the life-histor y trade-offs. In addition to changing development time and early fecundity in the direction predicted, high adult mortality affected three traits expr essed early in life-body size, growth rate, and ovariole number-but had lit tle or no effect on body composition (relative fat content), viability, met abolic rate, activity, starvation resistance, or desiccation resistance. Co rrelations among lines revealed trade-offs between early fecundity, late fe cundity, and starvation resistance, which appear to be mediated by differen tial allocation of lipids.