Estimating the relative fitness of local adaptive peaks: the aerodynamic costs of flight in mimetic passion-vine butterflies Heliconius

In a related paper, we demonstrated that mimetic Heliconius butterflies hav e converged in wing-beat frequency and degree of asymmetry in the wing moti on, whereas sister species are dissimilar in these same traits. Warning sig nals of sympatric, distasteful species converge in evolutionary models in o rder to educate their predators more efficiently that the signal is associa ted with unprofitable prey. Barring other constraints, the behaviours of th e different co-mimetic pairs should ultimately converge on that behaviour w hich minimizes the energetic cost of flight. We estimated the energetic cos t of each mimic's flight behaviour in order to predict the difference in he ight of each fitness peak and the direction of convergent selection qualita tively. Following adjustments for body mass, mimetic Heliconius melpomene a nd Heliconius erato required more aerodynamic power than Heliconius cydno a nd Heliconius sapho. This difference was attributed to the slower flight sp eeds and higher wing-beat frequencies of H. melpomene and H. erato. Consequ ently, H. melpomene and H, erato expended more energy per unit distance per unit body mass than H. cydno and H. saaho. However, differences in body ma ss may equalize energy budgets and stabilize the sympatric coexistence of t he two pairs of co-mimics.