Sexual selection, growth compensation and fast-start swimming performance in Green Swordtails, Xiphophorus helleri

1. Fast-start swimming provides an integrated physiological index of performance and a measure of ability to escape predators, so may be expected to covary with other important composite life-history traits such as growth rate. 2. Variation in resource availability during growth and development is common, and organisms may show compensatory responses (such as catch-up growth) to periods of low food availability. However, such responses usually carry costs. 3. We examined fast-start performance in adult Green Swordtails in relation to growth regime experienced as a juvenile. In contrast to previous studies we found that conditions experienced early in life did not significantly affect fast-start swimming performance, indicating that escape ability is at a premium in green swordtails. 4. Fish raised on ad libitum food had similar performance to fish raised on a restricted diet and fish experiencing compensatory growth, controlling for body size. 5. Body depth was positively related to fast-start performance in both males and females, with males having faster escape responses than females for a given body depth. 6. Remarkably, males with the relatively longest sexual ornaments ('swords') had the greatest escape ability, suggesting that sword length may be a good indicator of quality among males of similar age.