WOODS JR, W. A.*; WOOD, C. A. L. ; STEVENSON, R. D. ; University of Massachusetts Boston; Lincoln, MA; University of Massachusetts Boston: Detecting Interindividual Variation in Resting Metabolic Rate of the Painted Lady Butterfly Vanessa Cardui: Why You Should Not Offer Ladies Lunch

Questions about the adaptive significance of metabolic rate can be approached only when measurements of differences between individuals are repeatable. We made daily measurements of CO₂ production, body mass and food uptake over the adult lifespan of unmated Vanessa cardui that were kept under constant conditions of temperature and humidity in both fed and unfed treatments. Fed butterflies lived for 16.0 ±3.3 days (mean ±SEM) and unfed for 4.4 ±0.7 days, with females living longer than males in both treatments. CO₂ production and mass generally declined with age in both treatments, though with much day to day variability in the fed treatment. For unfed butterflies that lived for at least 3 days of measurement, differences between individuals in CO₂ production were only somewhat repeatable (r = 0.40); for fed butterflies, the differences were not repeatable (r = -0.12). However, removing age effects by standardizing CO₂ production values to each day’s highest value yielded high repeatability in the unfed treatment (r = 0.80), though not in the fed treatment (r = -0.07). Individuals� feeding history explained little variation in CO₂ production. We conclude that for V. cardui and possibly for other insects of similar feeding habit, variation in metabolic rate between individuals is best represented by measurements of unfed individuals of the same age.