Effects of temperature experienced across life stages on morphology and flight behavior of painted lady butterflies (Vanessa cardui)

Background: With ongoing anthropogenic climate change, there is increasing interest in how organisms are affected by higher temperatures, including how animals respond behaviorally to increasing temperatures. Movement behavior is especially relevant here, as the ability of a species to shift its range is implicitly dependent upon movement capacity and motivation. Temperature may influence movement behavior of ectotherms both directly, through an increase in body temperature, and indirectly, through temperature-dependent effects on physiological and morphological traits that can influence movement. Methods: Here, we investigate the influence of ambient temperature during two life stages, larval and adult, on body size and movement behavior of the painted lady butterfly ( Vanessa cardui ). We reared painted ladies to emergence at either a “low” (24 °C) or “high” (28 °C) temperature. At eclosion, we assessed flight behavior in an arena test, with half of the adults emerging from each rearing treatment tested at either the “low” or “high” temperature. We had a total of four treatment groups: the control (reared and tested at 24 °C), a consistently high temperature (reared and tested at 28 °C), and two treatments in which butterflies experienced flight tests at a temperature either higher or lower than the one at which they were reared. We measured adult body size, including wingspan, and determined flight speed, distance, and duration from video recordings. Results: Adult butterflies that experienced the higher temperature during development were larger. We documented an interaction effect of rearing x testing temperature on flight behavior: unexpectedly, the fastest butterflies were those who experienced a change in temperature, whether an increase or decrease, between rearing and testing. Conclusions: Individuals that experienced matching thermal environments flew more slowly, but for more time and covering more distance. Overall, the influence of body size per se on flight was minimal. We conclude that the potential role of “matching” thermal environments across life stages has been underinvestigated with regard to how organisms may respond to warming conditions.