Repeatable Behavioural Variation and Rapid Acclimation to Temperature in an Ectotherm

Consistent behavioural differences between individuals have been recognised in species across many taxa, termed ‘Animal Personality’. This has stimulated a large body of promising research, including growing evidence for individual differences in behavioural plasticity – differences in how individuals respond to an environmental gradient (biotic or abiotic factors) – and their potential relationship to personality. When differences in behavioural averages or behavioural plasticity are consistent this suggests that behavioural variation may have evolved adaptively and standing variation may allow continued adaptation under changing conditions. Robust understanding of the potential adaptive value and proximate causes of individual behavioural variation, requires establishing that these differences are consistent over time – they are ‘repeatable’. I investigated this by repeatedly measuring an anti-predator response (conglobation latency) in 100 common pillbugs (A. vulgare) under ambient temperature (16), and an acute increase in temperature (21c) for two days, repeated weekly. Each animal was assayed twice daily, for two days at each of two temperatures, over three consecutive weeks. This high number of individuals and repeated measures produced a data set sufficient for the data hungry assessment of thermal response repeatability (Nobs = 1967). I assessed temperature impacts on individual mean anti-predator behaviour, individual variance in behavioural plasticity, and the repeatability of these traits. Analyses indicated a significant but diminishing effect of temperature on reducing conglobation latency over the three weeks. Individuals showed highly repeatable personality (Rint = 0.81) but low and not significant repeatability of individual differences in behavioural plasticity (Rslope =0.06). The low Rslope value was caused by the near absence of individual differences in plasticity in the third week of assays. My results are a novel contribution to the literature on the repeatability of behaviour and behavioural plasticity, demonstrating very rapid adaptation to increases in temperature via acclimation.