Quantifying the direct and indirect costs of reproduction

The energetic costs of reproduction remain incompletely resolved, despite being fundamental to life history theory. Recent work has drawn attention to indirect costs of reproduction and suggested that they may be underestimated in energy budget models. However, a challenge in the study and modelling of indirect reproductive costs is that definitions change conceptually between reproductive modes. Here, we offer a consistent and generalizable definition by taking the perspective of the mother rather than the empirical researcher. From our proposed perspective, the mother’s energy costs are partitioned into what she provisioned to the embryo (direct costs) and the energy expended to do the provisioning (indirect costs). This conceptual approach can be implemented quantitatively through a model that can quantify embryonic development and associated dissipation. We illustrate how the Dynamic Energy Budget (DEB) theory allows such a quantification and what it implies about the empirical data necessary for a complete accounting of the energetic costs of reproduction.