Personality, plasticity and predictability in sticklebacks: bold fish are less plastic and more predictable than shy fish

Abstract

It is well established that animals often differ consistently from one another in their behaviour. Most work has focused on consistent differences in average behaviour, generally referred to as ‘animal personality’. However, individuals may also differ consistently from one another in how they change their behaviour over time or across environments, that is, plasticity, as well as in the predictability of their behaviour. How these three sources of behavioural variation are linked is rarely explored. Here we tested 80 wild-caught three-spined sticklebacks, Gasterosteus aculeatus, repeatedly over a 10-week period for their tendency to explore an open arena from the safety of cover, generally termed ‘boldness’. Using a mixed-modelling approach, we detected consistent individual differences in boldness, as well as in the extent to which fish changed this behaviour over time, that is, temporal plasticity. Boldness and plasticity were negatively correlated, with shy fish spending increasing amounts of time out of cover while bold fish changed little over time. After accounting for variation in personality and plasticity, we still detected individual differences in intraindividual behavioural variation (‘IIV’), that is, individual predictability. This residual variation was linked to fish’ boldness score, with shy fish having higher IIV and thus being less predictable in their behaviour than bold fish. After a 4-week break from testing, individuals on average decreased their time out of cover again to baseline levels. However, shyer, more plastic fish showed the largest changes in behaviour. Statistical simulations show that our experimental data set has sufficient statistical power to provide accurate and precise variance parameter estimates. Together, our results provide strong evidence that individual variation in boldness is linked with behavioural plasticity and predictability. Establishing the evolutionary causes as well as fitness consequences of these links in behavioural variation is an exciting challenge for future research.