Predator recognition and anti-predatory behaviour in a recent aquatic invader, the killer shrimp (Dikerogammarus villosus)

Abstract

The killer shrimp (Dikerogammarus villosus) is one of the most recent and damaging aquatic invasive species in many parts of Europe, but information on how the species responds to predation pressures in recently invaded areas is very limited. We employed an open test arena to examine anti-predatory behaviour in killer shrimp exposed to either blank water or water conditioned with kairomones from the three-spined stickleback to simulate a predator threat. Killer shrimp spent much more time hiding in the presence of stickleback kairomones than when they were exposed to blank water. However, no significant difference was found in aggregation behaviour, and killer shrimp were strongly attracted to the scent of conspecifics regardless of predator threat. Given the strong selective pressures that fish predators can exert on native and invasive gammarids, our findings highlight the need to consider prey-predator interactions to better predict the dispersal and likely impact of killer shrimp into invaded ecosystems.