Open field trials (OFT)
The OFT is a generic and simple assay widely used across taxa to measure shy-bold variation related aspects of personality (e.g. exploration in a novel environment, anxiety-like behaviour, stress coping-style) ​. In this assay, a shrimp was placed within a tube positioned in the centre of the tank (Figure 1a) and allowed to acclimate for 120 seconds. The tube was then lifted out and movement tracked for a subsequent 240 seconds using Viewer. We extracted four behavioural traits from tracking data: Track Length, Area Covered, Wall Distance andFreezings (see Table 1 for definitions). Based on OFT behaviour in other taxa, our prediction is that bolder individuals will tend to show higher values for the first three traits (i.e. more active exploration of the arena and less thigmotaxis) but lower values for freezing . The latter prediction stems from the fact that freezing behaviour under perceived risk is a common component of behavioural stress response (e.g. the ‘flight-fight-freeze’ response) . These behaviours are widely used in studies of shy-bold variation based on similar assays applied in fishes . We consider this an appropriate starting point, but fully acknowledge that a priori predictions are naïve with respect to decapod biology in general (and N. heteropoda specifically).  Summary statistics for the original variables measured in the OFT assay are presented in Table S1.