Evidence for dispersal personality in the guppy across ecological conditions, with a minor effect of relative brain size

Individuals that disperse typically exhibit specific phenotypical traits that facilitate dispersal and settlement success, known as ‘dispersal syndromes'. Consequentially, characterizing dispersers is crucial to understand other processes such as metapopulation dynamics and biological invasions. One trait that may play a major, yet overlooked, role in dispersal is relative brain size. Larger brains, through enhanced cognition and behavioural flexibility, could both increase and decrease the costs of dispersal, depending on the ecological context. However, barely any effort has been made to investigate the link between brain size and dispersal, especially so at the individual level. Here, we tested the impact of brain size on dispersal behaviour, in both a stable and unpredictable environment. We used Trinidadian guppies Poecilia reticulata from lines artificially bred for large and small relative brain size. Fish were placed in a laboratory set‐up of interconnected tanks, where we quantified how likely and how fast they were to disperse between tanks under two ecologically relevant conditions: a stable (control) and unpredictable environment (experimental drought). Surprisingly, there was only limited evidence that large‐ and small‐brained guppies differed in dispersal behaviour in either ecological context. While we found no differences in dispersal behaviour between the large‐ and small‐brained lines, both overall dispersal speed and dispersal likelihood correlated negatively with individual relative brain size, but only during the first opportunity fish had to disperse. Generally, guppies reduced dispersal after experiencing an environmental drought. Regardless of brain size or ecological context, they exhibited consistent interindividual variation in their decision to disperse or to stay, indicating the existence of a dispersal personality trait. Our results are valuable in the current context of invasive alien species. Understanding what traits influence the success during the various steps of the invasion process is of major importance from both a fundamental and conservation perspective.