Cognitive performance and stress responsiveness in the Trinidadian Guppy: a multivariate approach

Cognition is vital for carrying out behaviours required for survival and reproduction. In animals, we now know that cognitive performance varies not just among species, but also among individuals within populations. While this variation is a prerequisite for contemporary natural selection, it is also true that selection does not act on traits in isolation. The extent to which cognitive traits covary with other aspects of phenotype (e.g. personality traits) is therefore expected to be an important factor in shaping evolutionary dynamics. Here we adopt a multivariate approach to test for spatial learning ability in a captive population of male Trinidadian guppies (Poecilia reticulata), and ask whether differences in cognitive performance are associated with (repeatable) differences in stress response behaviour. We focus on stress response for two reasons. First, functional links between cognitive traits and stress coping style have been hypothesised. Second, individual-level studies of cognitive performance typically rely on multiple testing paradigms that may themselves be a stressor. Thus, there is a risk that variation in stress responsiveness is itself a cause of apparent, but artefactual variance in cognitive ability. Using a set of fish exposed repeatedly to two distinct spatial learning tasks (maze layouts), and an acute stress response test (open field trial), we find differences among-individuals in task performance that are repeatable within- and across maze layouts. On average performance improves with experience in the first maze, consistent with spatial learning, but not in the second. In both mazes, there is among-individual variation in the trajectory of mean performance with trial number 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 thus 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 observed declines in performance across repeats 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.