The energetic cost of reproduction and its effect on optimal life-history strategies

Trade-offs in energy allocation between growth, reproduction and survival are at the core of life-history theory. While age-specific mortality is considered to be the main determinant of the optimal allocation, some life-history strategies, such as delayed or skipped reproduction may be better understood when also accounting for reproduction costs. Here, we present a two-pool indeterminate grower model that includes a survival and energetic cost of reproduction. The energetic cost sets a minimum reserve required for reproduction, while survival cost reflects increased mortality from low post-reproductive body condition. Three life-history parameters determining age-dependent energy allocation to soma, reserve and reproduction are optimized, and we show that the optimal strategies can reproduce realistic emergent growth trajectories, maturation ages and reproductive outputs for fish. The model predicts maturation phase shifts along the gradient of condition related mortality and shows that increased harvesting will select for earlier maturation and higher energy allocation to reproduction. However, since the energetic reproduction cost sets limits on how early an individual can mature, increase in fitness at high harvesting can only be achieved by diverting most reserve into reproduction. The model presented here can improve predictions of life-history responses to environmental change and human impacts because key life-history traits such as maturation age and size, maximum body size, and size-specific fecundity emerge dynamically.