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.