Is behaviour in a novel environment associated with bodily state in brown trout Salmo trutta fry?

摘要

Energetic status and body size are inconstant bodily states often considered to have feedback effects on behaviour. Feedbacks can be negative, like starvation-threshold feedbacks (lower state values=increased risk taking due to higher energy need, and vice versa), or positive, like state-dependent safety feedbacks (higher state values=lower vulnerability when expressing risky behaviours, and vice versa). Few studies have investigated feedback effects during the early-life survival bottleneck of territorial species, when rapid growth is particularly important to maintain competitive ability. We investigated effects of body size and energetic status on the emergence latency into an unknown environment in highly territorial brown trout fry. We manipulated energetic status using high and low food rations in different combinations over two consecutive periods. In contrast to results from other small-sized fishes, no general behavioural effects of energetic state were detected, but larger fish had on average shorter emergence latency. Starvation-threshold feedbacks were not supported, but the size effect favours the presence of a state-dependent safety feedback. When individuals were split into clusters characterised by long (>34s) and short (34s) emergence latency, a state-dependent safety feedback, based on energetic status, was found in the short-latency cluster. Positive state-dependent feedbacks may reflect the high level of competition among wild trout fry during the first summer, particularly among the more active individuals (i.e., from the short latency cluster). High state levels could be utilised to gain advantages over lesser competitors (e.g., to establish territories), particularly if the overall risk of starvation is higher than the risk of predation.