Grasshoppers alter jumping biomechanics to enhance escape performance under chronic risk of spider predation

P>1. Prey can increase the probability of escaping a predator attack by adopting either behavioural tactics that provide more time or less distance to escape or by increasing their escape performances. It is assumed that the ability to improve escape performances is reserved for species that respond to chronic predation risk by substantially altering morphological traits related to locomotion. This thinking is at odds with fundamental predictions of physiological stress theory that suggest performance should be enhanced both independently of and in addition to morphological change. 2. The purpose of this study was to determine whether and how prey raised under chronic risk of predation can improve their escape performance independent of conspicuous morphological changes. 3. We reared herbivore grasshopper in field mesocosms with and without disarmed hunting spiders and measured their outdoor jumping performance. Grasshoppers were then transferred to the laboratory where we measured the biomechanics of their jumping to elucidate mechanisms that differentiate performance between rearing treatments. We collected second generation nymphal offspring from the field mesocosms and measured their morphology and escape performances to reveal costs associated with antipredator responses. 4. Chronically scared grasshoppers made adjustments in jumping technique that enabled them to take-off 1 center dot 2 times faster, which, in combination with additional in-flight behavioural adjustments, led to 2 center dot 6 times longer jump distances. These improvements were independent of conspicuous morphological changes but were accompanied by attendant costs: grasshoppers reared in risky environments produced smaller and less athletic offspring than grasshoppers from risk free environments. 5. The results suggest that prey do not need to undergo conspicuous morphological changes in locomotor traits before they can improve escape performance, revealing an adaptive and possibly common aspect of physiological stress reaction to predation.