Abstract
It is well established that living in groups helps animals avoid predation and locate resources, but maintaining a group requires collective coordination, which can be difficult when individuals differ from one another. Personality variation (consistent behavioural differences within a population) is already known to be important in group interactions. Growing evidence suggests that individuals also differ in their consistency, i.e. differing in how variable they are over time, and theoretical models predict that this consistency can be beneficial in social contexts. We used three-spined sticklebacks (Gasterosteus aculeatus) to test whether the consistency in, as well as average levels of, risk taking behaviour (i.e. boldness) when individuals were tested alone affects social interactions when fish were retested in groups of 2 and 4. Behavioural consistency, independently of average levels of risk-taking, can be advantageous: more consistent individuals showed higher rates of initiating group movements as leaders, more behavioural coordination by joining others as followers, and greater food consumption. Our results have implications for both group decision making, as groups composed of consistent individuals are more cohesive, and personality traits, as social interactions can have functional consequences for consistency in behaviour and hence the evolution of personality variation.
Highlights
Living in groups is a widespread adaptation and its independent evolution in a diverse range of taxa suggests that benefits, for example from reduced predation risk[1], often outweigh costs, such as increased food competition[2]
While there is a wealth of evidence for the consequences of average levels of individual behaviour, little empirical effort has been focused on exploring the consequences of differences in within-individual variation that is independent of average levels of expression
The mean latency to first leave the refuge in these two trials was used as a measure of an individual’s “boldness”, i.e. their tendency to take risk. Confirming that this measure of boldness was associated with risk-prone behaviour, the time taken to cross the open arena was shorter in individuals with a greater boldness score (negative binomial Generalised Linear Mixed Model (GLMM), n = 71: χ21,65 = 14.9, P = 0.00011, Table S1)
Summary
Living in groups is a widespread adaptation and its independent evolution in a diverse range of taxa suggests that benefits, for example from reduced predation risk[1], often outweigh costs, such as increased food competition[2]. Performance during social coordination problems, for example, caring for offspring collectively, has been suggested to be a potentially important selection pressure on individuals to both differentiate from their social partners (divide the labour, see refs 21,22) and be predictable (consistent) while they do so[23,24] This explanation for the evolutionary persistence of such personality variation has only rarely been investigated[25] and the purported role for consistency per se remains untested. Collective foraging by fish in shoals (e.g. leader-follower behaviour from refuges26,27) requires that individuals remain coordinated with each other to gain protection from predators Groups such as fish shoals commonly show fission-fusion dynamics[28], where frequently changing group membership may not allow individuals to learn the behavioural traits of their groupmates even if their behaviour is consistent over time. Our study takes a similar approach to others which have explored the effects of variation in individual behaviour (e.g. average level of boldness) when tested alone on social interactions (e.g. refs 14,15,30,31)
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