Using a minimal model of metabolism, I examine the limitations of behaviour that is (a) solely in response to environmental phenomena or (b) solely in response to metabolic dynamics, showing that basic forms of each of these kinds of behaviour are incapable of driving survival-prolonging behaviour in all situations. Inspired by experimental evidence of concurrent metabolism-based and metabolism-independent chemotactic mechanisms in Escherichia coli and Rhodobacter sphaeroides, I then demonstrate that a simple switching mechanism can be sufficient to integrate the two sensitivities into an improved behaviour.

In the second part of the talk, I compare the robustness of metabolism-based behaviour and metabolism-independent behaviour.  The metabolism-based behaviour is remarkably adaptable, allowing an organism to adapt to radical changes in its environment and even in its own organisation. This part of the talk supports and clarifies aspects of behavioural metabolution, an evolution facilitating interaction between metabolism-based behaviour and genetic evolution.