Acoustic signalling performance: variation in vigour at multiple scales

Sexual displays can be energetically taxing, power-limited tests of endurance that favour the vigorous. Therefore, these displays may reliably indicate the ability to pay the energetic costs of sustained motor performance. Field cricket calling song involves the repeated mechanical movement of wings to produce pulses of sound grouped into species-specific chirp patterns, often sustained for long periods across nights. We quantified variation and repeatability of cricket calling song phenotypes and determined how age and body size impacted this variation. All our experiments involved tightly controlled signalling environments, but there was a great deal of interindividual variation in behaviour. Although there were species differences, most traits associated with signalling vigour exhibited mean level declines with age and conditional repeatability (individual*age interactions). These results suggest that males differing in quality may differ in their ability to buffer themselves against age-related changes in signalling vigour. Furthermore, the repeatability of calling traits itself changed with age, declining slightly in some species but increasing in others. We also challenged motor performance by altering dietary carbohydrate and protein; we predicted that increased carbohydrate would enhance signalling vigour and increased protein would decrease it. Although diet influenced the probability of calling and time spent calling in a predictable manner, these effects were not profound. Our findings confirm the scope for sexual selection to act on motor performance and point to ways in which constraints and trade-offs may yield variation within and among species in how vigour is signalled. Crown Copyright (c) 2021 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. All rights reserved.