Locomotor mimicry in butterflies? A critical review of the evidence

The hypothesis of locomotor mimicry in butterflies presented by Srygley ( Phil. Trans. R. Soc. Lond. B 343, 145—155 (1994)) is criticized as unparsimonious, from two perspectives. First, the existence of mimicry between palatable but unprofitable prey is disputed on theoretical and empirical grounds. The lack of a strong predator aversion stimulus seriously undermines the unprofitable prey scenario, and supposed cases of mimicry of unprofitable models are explicable by traditional mimetic modes. Second, correlations of phenotypic characters used to support alternative adaptive peaks for palatable and unpalatable butterflies are criticized for failing to account for phylogenetic relationships. Virtually all of the relevant variation in flight-related morphology is shown to be due to differences between clades, rather than mimicry groups. An alternative hypothesis emphasizing phylogenetic constraint in the evolution of morphological characters associated with predator avoidance is proposed. The ground rule — or perhaps doctrine would be a better term — is that adaptation is a special and onerous concept that should be used only where it is really necessary. When it must be recognized, it should be attributed to no higher a level of organization than is demanded by the evidence. In explaining adaptation, one should assume the adequacy of the simplest form of natural selection, that of alternate alleles in Mendelian populations, unless the evidence clearly shows that this theory does not suffice. G. C. Williams (1966, pp. 4—5).