SRYGLEY, R.B.: Locomotor Mimicry among Passion-vine Butterflies Heliconius

With regard to prey motion, the evolution of mimicry has been investigated in three areas: 1) locomotor mimicry, 2) anti-apostatic selection, and 3) escape mimicry. Locomotor mimicry is the similarity in motion of two distantly-related prey species. Because of evolutionary convergence in key morphological features that are relevant to flight, convergence in the flight behavior of distasteful, mimetic passion-vine butterflies in the genus Heliconius was predicted. Applying a methodology developed in C.P. Ellington’s laboratory, I present evidence that mimetic Heliconius are more similar in wingbeat frequency and the degree of asymmetry in the wing motion than they are to their sister species. Anti-apostatic selection, or selection against odd individuals, may be the selective force for behavioral similarity among M�llerian mimics. Prey motion increases selection against odd individuals when prey are at high densities, and perhaps when the prey are M�llerian mimics. Ultimately, the behaviors of the different mimetic morphs should converge on that behavior which minimizes the energetic cost of flight. Applying Ellington’s aerodynamic models, I estimated the energetic cost of each mimetic morph’s flight behavior in order to qualitatively predict the difference in height of each fitness peak and the direction of convergent selection. Following adjustments for body mass, mimetic H. melpomene and H. erato required more aerodynamic power than H. cydno and H. sapho. This difference was attributed to the slower flight speeds and higher wingbeat frequencies of H. melpomene and H. erato. From morphology, locomotor mimicry with important limitations is also predicted to occur in palatable species that appear like distasteful models (Batesian mimics), and among palatable species that are color mimetic due to unprofitable prey (or escape) mimicry.