Effects of weight loading on flight performance and survival of palatable Neotropical Anartia fatima butterflies

Previous studies show that the position of centre of body mass (cmbody) and the ratio of flight muscle to total body mass (flight muscle ratio, FMR) are good predictors of flight speed and manoeuvrability in butterflies. However, cmbody, FMR, and related morphometric traits are strongly correlated phenotypically, making it difficult to identify the causal determinants of flight performance. By experimentally gluing weights that amounted to >15% body weight to a palatable Neotropical butterfly species (Anartia fatima), we tested the effects of altering FMR and repositioning cmbody on two measures of flight performance: flight speed and the ability to evade capture. We then tested their effects on survival in a natural setting. Flight performance studies detected no significant differences in airspeed or evasive flight ability among unweighted controls, weighted-loaded butterflies (WL), and those with cmbody positioned further posterior (CM). In two mark-release-recapture experiments, survival of treatment groups did not differ, but males survived longer than females. In one experiment, WL and CM butterflies were recaptured more frequently than controls, whereas the probability of recapture for females was higher than that for males in the second experiment. When significant, results for recapture were consistent with a causal relationship between FMR and flight speed. Presumably, a decrease in flight speed was due to a reduction in muscle mass-specific power output in the weighted butterflies. However, the results did not support a relationship between manoeuvrability and cmbody.