Rapid shifts in behavioural traits during a recent fish invasion

Biological invasions are a prominent example of human-induced environmental change that pose a significant threat to worldwide biodiversity. Recent evidence suggests that behavioural traits play a key role in mediating invasion success. However, little research has investigated how rapidly behavioural traits can change during the initial stages of invasion. We investigated the influence of invasion on behaviour in a recent aquatic invader, the Siamese fighting fish (Betta splendens), in northern Australia. These fish represent a recent introduction (ca. 2010) and are thought to be descended from ornamental varieties released into the wild from the aquarium trade. Using fish reared under captive conditions, we measured differences in three ecologically relevant behaviours (activity, foraging, and aggression) across invasive and domestic fighting fish. We found that fish descended from the recent invasive population were more active and consumed fewer food items than their domestic counterparts. Furthermore, foraging latency was repeatable in invasive, but not domestic fish, and this seemed to be driven by an increase in among-individual variation in the invasive population. Finally, while we detected a positive relationship between activity and number of food items eaten in domestic fish, this relationship was absent in the invasive population, suggesting that invasion may have disrupted this behavioural syndrome. Our results highlight that invasion can alter ecologically important behavioural traits and behavioural syndromes, even during the initial stages of invasion, and emphasise the importance of incorporating behaviour into our understanding of invasion biology. SIGNIFICANCE STATEMENT: Alien species must rapidly adapt to novel environmental conditions in order to establish a successful invasive population. As behaviour mediates how organisms interact with their environment, behavioural traits may play a key role in facilitating invasion success. We investigated rapid changes in behavioural traits in a recently introduced (ca. 2010) ornamental fish, the Siamese fighting fish. We found that invasive fish differed from their domestic source population in two key behavioural traits—activity and foraging behaviour. Furthermore, we extend previous work by showing that invasion not only causes changes in average-level behavioural traits but can also result in changing patterns of behavioural variation and repeatability in newly established populations. Overall, our findings highlight that invasion can induce shifts in ecologically relevant behaviours, even during the early, crucial stages of invasion.