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 (cm(body)) a nd the ratio of flight muscle to total body mass (flight muscle ratio, FMR) are good predictors of flight speed and manoeuvrability in butterflies. Ho wever, cm(body), FMR, and related morphometric traits are strongly correlat ed phenotypically, making it difficult to identify the causal determinants of flight performance. By experimentally gluing weights that amounted to si milar to 15% body weight to a palatable Neotropical butterfly species (Anar tia fatima), we tested the effects of altering FMR and repositioning cm(bod y) on two measures of flight performance: flight speed and the ability to e vade capture. We then tested their effects on survival in a natural setting . might performance studies detected no significant differences in airspeed or evasive flight ability among unweighted controls, weighted-loaded butte rflies (MIL), and those with cm(body) positioned further posterior (CM). In two mark-release-recapture experiments, survival of treatment groups did n ot differ, but males survived longer than females. In one experiment, WL an d 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 dec rease 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 cm(body). (C) 2000 The Linnean Soc iety of London.