Can behavioural constraints alter the stability of signalling equilibria?

In traditional models of signalling one class of individual, the signaller, presents a signal which another class of individual, the receiver, examines. Receivers are typically assumed to have fitness returns that depend on their ability to determine the utility of the signaller to them. Each signaller must decide what level to signal at, which is a function of the quality of the signaller. In addition, a signaller's quality is assumed to be synonymous with the signaller's utility to a receiver. However, there is no reason to believe that signalling costs are incurred in the same currency as the receivers are paid and, thus, no reason to believe that the relationship between signaller quality and utility is linear or even increasing. For instance, in signalling between prey and predators, the utility of a prey item may be its fat reserves, whereas an individual prey pays for signalling (and thus measures quality) in terms of increased risk of capture; quality and utility are synonymous only if a high risk of capture is associated with high fat reserves. In addition, several recent studies have documented increased signalling as utility decreases. If utility and quality are decoupled, so that increasing quality does not always mean increasing utility, then traditional signalling models predict that no signalling equilibrium will exist. I show that if receiver fitness is modelled by a set of behavioural responses, which have both costs and benefits, then a signalling equilibrium can sometimes be recovered. An example of signalling between mates is presented in order to demonstrate this equilibrium.