BRANDT, Y.; Indiana University, Bloomington: Diminished Locomotor Performance: a tool for Quantifying Display Costs

Handicap models of signaling propose that display honesty can be maintained by variation in display costs, since the fitness benefits of increasing signal expression are offset by increasing fitness costs. Testing this hypothesis requires a practical means of measuring the fitness costs of display expression. Display costs have been quantified either by measuring increases in energetic expenditure or reduced survival rates, but these measures are frequently unsatisfactory. Energetic expenditure does not translate to fitness consequences when energy is not a limiting resource while survival is typically difficult to measure in relation to variability in display traits. In contrast, systems in which individual variation in locomotor performance is known to affect fitness offer an excellent, though seldom exploited means of measuring fitness-relevant display costs. Locomotor performance can impact fitness by affecting foraging success, escape from predators and social interactions. In such systems, display cost can be quantified by measuring the decrement in locomotor performance that display expression engenders. As in Arnold’s influential morphology-performance-fitness paradigm, this approach to quantifying display costs is efficient because the impact of display expression on performance can be elucidated under controlled laboratory conditions, while the relationship between performance and fitness can be documented in field studies. Unlike alternative approaches to measuring display costs, diminished locomotor performance is both directly measurable and linked to fitness.