Risk-taking and locomotion in foraging threespine sticklebacks (Gasterosteus aculeatus): the effect of nutritional stress is dependent on social context

The relationship between individual physiological traits and social behaviour is an important research area because it can examine how mechanisms of behaviour link to functional outcomes. It is hypothesised that correlative and causative links between physiology and individual behaviour may be altered by social interactions. Here, we assess how nutritional stress (20-h starved, 90-h starved) and routine metabolic rate (RMR) determine the movement and foraging behaviour of threespine sticklebacks (Gasterosteus aculeatus), both individually and in a social context. Results showed that there was no statistically significant relationship between RMR and behaviour. The nutritional stress treatment had significant opposite effects on voluntary swim speed, dependent on whether fish were assayed asocially (alone) or socially (in shoals of three). Greater nutritional stress caused voluntary swimming speeds to reduce in an asocial context but increase in a social context, although both relationships were not significant. Additional results exploring social behaviour parameters such as the frequency and duration of shoaling interactions suggests that alterations in fish swim speed between the two nutritional stress treatments may be due to competition effects. This study links state-dependent individual behaviour to social foraging performance and reinforces the theory that social context is an important modulator of the relationships between physiology and behaviour. Recent research has highlighted that the social environment may shape how physiology and behaviour are linked. This area of research, however, requires data from empirical studies that measure and experimentally manipulate physiological traits of individually identifiable animals and tests them under asocial and social conditions. Using threespine sticklebacks foraging for bloodworms, we show that routine metabolic rate did not have a statistically significant effect on fish locomotion or risk-taking. Greater nutritional deprivation caused fish to decrease their swimming speed when they were alone (likely in an effort to reduce energy expenditure); however, when assayed in groups, competitive forces between shoal mates caused them to swim at faster voluntary speeds. Nutritional stress therefore had a significant socially dependent effect on fish locomotion.