Crickets become behaviourally more stable when raised under higher temperatures

Abstract

Developmental plasticity “prepares” individuals to environments experienced during adulthood. Labile traits, such as behaviour, vary within and among individuals owing to (i) reversible plasticity and (ii) developmental plasticity and genetic make-up, respectively. Here, we test whether developmental environments affect the expression of both within- and among-individual variation in behaviour. In ectothermic species, low temperatures are associated with a reduced expression of behaviour and can also limit the expression of reversible plasticity and among-individual differentiation, for example, by restricting the expression of additive genetic variation. We focused on exploratory behaviour since activity-related behaviours are assumed to be temperature-dependent in ectotherms. Specifically, low temperatures can restrict the physiological machinery needed for movement. To test our predictions, we raised field crickets, Gryllus bimaculatus, at low versus high temperatures throughout ontogeny and compared behavioural means and variance components (i.e. among- and within-individual variances) across treatments. We also compared the coefficients of variation for each variance component across treatments to assess whether environmental effects on variance were independent of the effects on mean behaviour. As predicted, individuals raised at high temperatures were more explorative and exhibited more among- and within-individual variance compared to individuals raised at low temperatures. Interestingly, individuals raised under high temperatures became more stable in their behaviour when controlling for treatment effects on average behaviour. Our results show experimentally that different developmental temperatures trigger different amounts of behavioural “stability” in exploratory behaviour, thereby suggesting a key role for temperature in affecting the ecological processes associated with exploratory behaviour in ectothermic species. Individuals differ relative to one another in their mean behavioural expression (i.e. “animal personality”), while, at the same time, individuals change their behaviour from one instance to the next (i.e. reversible plasticity). Expression of both above-mentioned components should strongly depend on environments experienced throughout ontogeny. Temperature represents a key environmental factor in most ectothermic animals as it directly affects the ability to express behaviour. Here, we experimentally test whether temperature experienced throughout ontogeny has permanent effects on the expression of individual differences and reversible plasticity in behaviour later in life. We show that individuals become more stable, i.e. express less reversible plasticity, in risky exploratory behaviour when raised under high temperatures. Our results thus suggest a key role for temperature in affecting the ecological processes associated with risky behaviours in ectothermic species.