1. According to a recent hypothesis, personality traits should form integrative pace-of-life syndromes with life-history traits. Potential life-history traits that explain personality variation are immune defence and growth rate.
2. We studied whether boldness, measured as hiding behaviour, is repeatable during ontogeny in the field cricket, Gryllus integer, and if it relates to the efficiency of immune function (i.e. the capacity to encapsulate a nylon implant), growth rate, developmental time and size as an adult.
3. Hiding behaviour was rank-order repeatable, and in general, juveniles were bolder than adults. Individuals that were cautious at early juvenile stages had higher encapsulation responses late in life compared with bold individuals. Most clearly, fast-growing individuals matured early and invested little in immune defence compared with their slower-growing conspecifics, i.e. showed patterns of a ‘grow fast, die young’ life-history strategy.
4. Our results may arise from a trade-off between immunity-dependent survival and bold behaviour. Trade-offs between investment in survival and behaviour could account for the maintenance of variation in personality traits by favouring certain combinations of behavioural and life-history strategies (i.e. pace-of-life-syndromes).