Responses to threat in a freshwater invader: Longitudinal data reveal personality, habituation and robustness to changing water temperatures in the ‘killer shrimp’ Dikerogammarus villosus (Crustacea: Amphipoda).

Freshwater biodiversity and ecosystem integrity are under threat from biological invasions. The ‘killer shrimp’ Dikerogammarus villosus is a highly predatory amphipod which has spread readily across Central Europe and recently the U.K. and its arrival has been associated with the significant loss of resident species. Despite this, studies of its behavioural ecology are sparse, even though its behaviour may contribute to its invasion success. For the first time we investigated anti-predator ‘fleeing’ behaviour in D. villosus and how this changed with water temperature. Three key patterns emerged from our analysis. First, within a particular temperature condition there are moderate but consistent among-individual differences in behaviour. These are driven by a combination of mean level among-individual differences and within-individual relative consistency in behaviour, and provide the key marker for animal personalities. Second, the fleeing responses were not influenced by temperature and thirdly, regardless of temperature, all individuals appeared to habituate to a repeated non-dangerous stimulus, indicating a capacity for individual-learning. We suggest that the anti-predator behaviour of D. villosus contributes to its rapid spread and that consistent among-individual differences in behaviour may promote biological invasions across heterogeneous conditions. Robustness to changing water temperatures may also be potentially advantageous, particularly in an era of global climate change, where average temperatures could be elevated and less predictabl