Egg maturation, nest state, and sex ratios: a dynamic state variable model

Background: Parents can invest in offspring through a variety of behaviours. Optimization models of these behaviours are usually based on determination of the single 'factor' parents optimize for a given set of conditions. Interactions between factors are rarely considered. Question: Do mothers optimize a single factor related to the investment in offspring (e.g. current nest state or mature egg state), or do mothers find an optimal balance between these two in relation to maximizing lifetime reproduction? Methods and key assumptions: A dynamic state variable model. We develop a 'hybrid' model that examines mothers' allocation decisions to offspring by considering mature egg and nest state as well as other environmental/ecological factors. We assume that mothers alter reproductive decisions based on their perception of costs and benefits of brood cell and nest construction. Some of these construction behaviours determine investment in one or a few offspring within a brood but others affect the entire brood. Egg maturation rate is a constant. Conclusions: Our results demonstrate that there is no single limiting factor; instead, there is some 'optimal balance' between mature egg and nest state that determines the optimal reproductive decision.