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.