A recent study found that guppies (Poecilia reticulata) can be trained to discriminate 4 versus 5 objects, a numerical discrimination typically achieved only by some mammals and birds. In that study, guppies were required to discriminate between two patches of small objects on the bottom of the tank that they could remove to find a food reward. It is not clear whether this species possesses exceptional numerical accuracy compared with the other ectothermic vertebrates or whether its remarkable performance was due to a specific predisposition to discriminate between differences in the quality of patches while foraging. To disentangle these possibilities, we trained guppies to the same numerical discriminations with a more conventional two-choice discrimination task. Stimuli were sets of dots presented on a computer screen, and the subjects received a food reward upon approaching the set with the larger numerosity. Though the cognitive problem was identical in the two experiments, the change in the experimental setting led to a much poorer performance as most fish failed even the 2 versus 3 discrimination. In four additional experiments, we varied the duration of the decision time, the type of stimuli, the length of training, and whether correction was allowed in order to identify the factors responsible for the difference. None of these parameters succeeded in increasing the performance to the level of the previous study, although the group trained with three-dimensional stimuli learned the easiest numerical task. We suggest that the different results with the two experimental settings might be due to constraints on learning and that guppies might be prepared to accurately estimate patch quality during foraging but not to learn an abstract stimulus-reward association.

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The integration of traits into ‘syndromes' has been suggested as a useful framework to advance insights in trait responses to environmental stressors. Yet, how stressors shape the consistency (‘repeatability') of traits and their covariation at the individual level remains debated. We studied how seasonal time constraints shape trait repeatability and integration of life‐history, behavioural and physiological traits along a fast–slow continuum, using the ‘pace‐of‐life syndrome' as a framework. We manipulated the photoperiod during the larval development of the damselfly Ischnura elegans, generating a time‐relaxed early, a control, and a time‐constrained late group. The photoperiod treatment did not seem to affect the voltinism of the larvae. As predicted, late‐period larvae accelerated development and growth, yet this acceleration was no longer detectable for growth and metabolic rate during the final instar, possibly due to costs of the initial life‐history acceleration. This warrants caution when inferring a species' pace‐of‐life based on a specific developmental stage. The late‐period larvae were as predicted more active (only during the later stages of the final instar) and bolder than the control larvae, but not different from the early‐period larvae. Most studies on time constraints only compared late and control animals, thereby potentially wrongly concluding adaptive responses to time constraints. Activity, boldness and body mass were repeatable, while growth and metabolic rates were not. Notably, repeatabilities did not change under time constraints. There was no support for an overall trait integration in a pace‐of‐life syndrome, yet activity and boldness covaried positively as expected. Importantly, this ‘behavioural syndrome' was decoupled in the late‐period larvae, which might be adaptive to enhance energy acquisition to fuel the accelerated development rate. Our results suggest that besides the predicted plastic acceleration of life‐history, plastic changes in behavioural trait integration may also be an important but overlooked adaptive aspect of responding to time constraints.