Unreplicable state‐dependent effects on start‐box emergence latency in wild‐origin sticklebacks

Animals are predicted to adjust their behaviour in relation to their bodily energetic state. Adjustment can be driven by either positive feedbacks (e.g. increased risk‐taking with higher energetic status; “state‐dependent safety”) or negative feedbacks (e.g. reduced risk‐taking with higher status; “asset protection”). This study investigated effects of food restriction and subsequent refeeding on boldness‐like behaviour in three‐spined sticklebacks (Gasterosteus aculeatus) and nine‐spined sticklebacks (Pungitius pungitius). The same experimental design was run in 2 consecutive years, using a start‐box emergence test to score behaviour, aiming for an exact replication in the second year. Results indicate that the results from the original and the replicated experiment did not match. Both years there was support for treatment effects, but the effects were qualitatively and quantitatively different. In 2012, the fish on a continuous high ration had longer emergence times than restricted‐refed fish (suggesting asset protection as the feedback mechanism), while in 2013, this pattern is reversed (suggesting state‐dependent safety as the feedback mechanism). In 2013, the general emergence time was also generally shorter than in 2012. These effects suggest that the methodology used may not be particularly robust. Subject fish were wild‐caught, and differences in the populations across years, or in the individuals' prior experience, may have influenced the results. Alternatively, the start‐box emergence test could be sensitive to minor (unperceived) alterations in procedures. Regardless, the present study suggests that the robustness of the start‐box emergence test, which is a commonly used test (e.g. to score “boldness” in animal personality experiments) needs further investigation. In addition to the behavioural experiment, fish going through the refeeding protocol were shown to have higher body water content than fish on a continuously high food ration in both species. Food restriction also decreased relative liver mass in the short term, but it was restored during refeeding.