Inter-individual variation in shivering behaviour in the migratory painted lady Vanessa cardui

1. Thermoregulation abilities are likely to play a fundamental role in ectotherms' response to current environmental changes, including through their implication in interspecies and interindividual variations in life-history strategies (e.g. dispersal syndromes). However, differences in thermoregulatory behaviours, and especially interindividual differences, are largely neglected in the literature, and there is still no global understanding of their importance in determining population and evolutionary processes, even in extensively studied taxa such as butterflies. 2. Interindividual variation in shivering in the painted lady, a migratory butterfly, was investigated. This behaviour has been very poorly studied, despite being widespread in insects in general, including butterflies. Using a warming experiment in the laboratory on 94 different individuals caught in the wild during the same migratory event, interindividual variation in shivering behaviour was investigated, and the effects of wing morphology and boldness (a behavioural axis known to be associated with mobility in butterflies) on shivering decision and efficiency were tested. 3. The study shows that individuals strongly differ in their shivering behaviour. Wing morphology affected both individuals' decision on whether or not to use shivering and heating rate while shivering. In contrast, no effect was found of individuals' age and boldness on shivering decision and efficiency. The findings also reveal that shivering strongly increased heating rate and allowed higher flight temperatures to be reached, while bolder individuals also took off at higher temperatures. 4. Overall, the results of the present study underline how variation in a neglected thermoregulatory behaviour could affect general life-history strategies in butterflies, and stress the need to consider this behaviour when investigating butterfly life-history syndromes.