Current energy state interacts with the developmental environment to influence behavioural plasticity

There is increasing evidence that among-individual differences in behaviour are, in part, generated by environmental effects. For example, diet quality can have drastically different effects on behavioural variation depending on whether it acts primarily during ontogeny (i.e. as a permanent environmental effect) or has an immediate effect on trait expression as a consequence of energy intake (i.e. temporary source of variation). Moreover, whether diet quality has a stronger effect on a trait's average expression, its variance or its covariance with other traits, remains unclear. We used a 2×2 factorial design crossing life stage (juvenile and adult) and diet quality (low- or high-energy content) to disentangle the effects of developmental and adult diets on the expression of behavioural differences. We tested 281 crickets for their activity levels, responses to predator cues and body mass. Neither developmental diet nor adulthood diet had any effect on population means or on the expression of an activity–antipredator response syndrome, suggesting a genetic basis for this syndrome. We did find evidence for increases in the within-individual variance as a result of exposure to a high-quality diet. However, these increases were only found for antipredator response and body mass. This indicates that diets with higher energy content can increase the potential for behavioural plasticity in antipredator response. In addition to changes in within-individual variation in behaviour, diet quality during development also mediated the links between maturation time and exploratory behaviours. More exploratory crickets matured faster when exposed to the low-quality developmental diet, but this relation was absent in the high-quality diet treatment. Our results show that changes in developmental diet quality can mediate the relationship between life history and behavioural traits later in life. •Differences in diet quality can be a major source of behavioural variation.•We examined the effect of diet quality on cricket activity and antipredator response.•Diet quality had no effect on trait average or the correlation among traits.•Crickets fed a high-quality diet showed greater plasticity in antipredator response.•Our results suggest diet quality can mediate the costs of behavioural plasticity.