Exploring physiological constraints on life-history traits using Dynamic Energy Budgets

A current challenge in predicting species responses to global change is to understand evolutionary responses to rapidly changing environments and novel environmental conditions. It has been hypothesised that the speed of evolution would be contingent uponhighly dependent on evolutionary constraints shaped by resource allocation trade-offs and other physiological mechanisms underlying the expression of traits. However, the majority of models employed to investigate life-history evolution remain phenomenological in nature. They fail to incorporate realistic mechanisms for the transfer and transformation of resources that are in accordance with the established laws of physics and chemistry. Our objective was therefore to explore the full range of life-history strategies that are genuinely available to organisms through realistic metabolic processes and to compare them with the predictions made by classical life-history theories. To this end, we employed the Dynamic Energy Budget (DEB) theory to model the energy allocation of individuals. We studied inter-individual variation by varying the value of energetic primary parameters (i.e. physiological processes) of the model, under constant environmental conditions (optimal temperature and ad libitum food source). Physiological processes that impact both growth and reproduction, such as energy acquisition, allocation and mobilisation, were found to reproduce the predictions of life-history theory to a certain extent. However, some discrepancies remained, mainly because DEB theory accounts for physiological retro-actions that are not articulated in life- history theories. For example, quicker growth had an indirect impact on reproduction and ageing through respectively increased resource acquisition and dilution of damage-inducing compounds. Based on those insights, we propose future directions to integrate physiology, and in particular metabolism, into models of life-history evolution.