Seasonality in Offspring Value and Trade-Offs with Growth Explain Capital Breeding

The degree to which reproduction is based on reserves (capital breeding) and/or current acquisition (income breeding) drives extensive variation in organism life histories. In nature, pure income and capital breeding are endpoints of a continuum of diversity whose ultimate drivers are poorly understood. To study the adaptive value of capital and income breeding, we present an annual routine model of the life history of a perennial organism where reproductive value at birth varies seasonally. The model organisms allocate time and resources to growth, reproduction, and storage. Our model predicts that capital breeding is adaptive when timing of birth affects offspring reproductive value. The stronger the seasonality, the more time is dedicated to capital breeding and growth after maturation (indeterminate growth) instead of income breeding. This is because storage and growth are investments in future (residual) reproduction taken at times when offspring value is low. Storage is a short-term investment in offspring through capital breeding; growth is a long-term investment in reproductive potential. Because the modeled production rate increases less than linearly with body size, growth brings diminishing returns for larger organisms, favoring capital breeding. Building storage requires time, which limits growth opportunities, and we show for the first time that in seasonal environments, the degree of capital breeding is tightly linked to body size of indeterminate growers through allocation trade-offs.