Individual differences in spatial learning are correlated across tasks but not with stress response behaviour in guppies

Abstract

Cognition is vital for carrying out behaviours required for survival and reproduction. Cognitive performance varies among species, but also among individuals within populations. While variation is a prerequisite for natural selection, selection does not act on traits in isolation. The extent to which cognitive traits covary with other aspects of phenotype (e.g. personality traits) may be important in shaping evolutionary dynamics. Here we adopt a multivariate approach to test spatial learning in male Poecilia reticulata, and ask whether differences in cognitive performance are associated with (repeatable) differences in stress response behaviour. Functional links between cognitive traits and ‘stress coping style’ have been hypothesised. Furthermore, individual-level studies of cognitive performance typically rely on multiple testing paradigms that may themselves be a stressor. There is a risk that variation in stress responsiveness is itself a cause of apparent, but artefactual variance in cognitive ability. Fish repeatedly experienced two spatial learning tasks (maze layouts), and an acute stress response test (open field trial). We find repeatable differences among-individuals in performance within- and across maze layouts. On average performance improves with experience in the first maze, consistent with spatial learning, but not in the second. There is among-individual variation in the trajectory of mean performance with trial number in both mazes, suggesting individuals differ in ‘learning rate’. Acute stress response behaviour is repeatable but predicts neither average time to solve the maze nor learning rate. We find no support for among-individual correlation between acute stress response and cognitive performance. However, we highlight the possibility that cumulative, chronic stress effects may nonetheless cause declines in performance for some individuals (leading to lack of improvement in mean time to solve the second maze). If so, this may represent a pervasive but difficult challenge for our ability to robustly estimate learning rates in studies of animal cognition