Are “early birds” bolder? Early daily activity is not correlated with risk-taking behaviour in a major invasive species

ABSTRACT Daily behavioural rhythms provide ecological advantages with respect to exploitation of food resources and avoidance of predation and recent studies suggested that timing of activity could form a behavioural syndrome with risk-taking behavior. Behavioural syndromes are often displayed by invasive species but the role of activity rhythms in biological invasions is unknown. Here, we investigated whether early nocturnal activity (the relative amount of locomotor activity displayed early in the night) and risk-taking behaviour (i.e. response to a scare stimulus) form a behavioural syndrome in a major invasive species, the signal crayfish ( Pacifastacus leniusculus ). We first characterized daily rhythms of locomotor activity over five days under controlled laboratory conditions and then scored the response to a scare stimulus across two different contexts (neutral and food) two days apart within the following six days. Crayfish displayed overall daily activity rhythms peaking in the first four hours of darkness. Both early nocturnal activity and risk-taking behaviour showed consistent inter-individual differences with repeatability scores of 0.20 and 0.35, respectively. However, the two behavioural traits were not correlated as in a behavioural syndrome. We argue that in contrast to other behavioural syndromes, a link between early nocturnal activity and risk-taking tendency would not be evolutionary stable as it dramatically increases predictability and therefore predatory pressure to individuals. We suggest that daily activity rhythms and risk-taking behavior can be important traits in understanding the adaptations underlying biological invasions or other processes of contemporary evolution.