Are mimics monophyletic? The necessity of phylogenetic hypothesis tests in character evolution

BACKGROUND: The processes governing the origin and maintenance of mimetic phenotypes can only be understood in a phylogenetic framework. Phylogenetic estimates of evolutionary relationships can provide a context for analyses of character evolution; however, when phylogenetic estimates conflict, rigorous analyses of alternative evolutionary histories are necessary to determine the likelihood of a specific history giving rise to the observed pattern of diversity. The polyphenic butterfly Limenitis arthemis provides a case in point. This species is comprised of three lineages, two of which are mimetic and one of which is non-mimetic. Conflicting estimates of the relationships among these three lineages requires direct evaluation of the alternative hypotheses of mimicry evolution. RESULTS: Using a coalescent framework, we found support for a sister-taxon relationship between the non-mimetic L. a. arthemis and the mimetic L. a. astyanax, congruent with the previous hypothesis that the non-mimetic form of L. a. arthemis was derived from a mimetic ancestor. We found no support for a mimetic clade (L. a. astyanax + L. a. arizonensis) despite analyzing numerous models of population structure. CONCLUSIONS: These results provide the foundation for future studies of mimicry, which should integrate phylogenetic and developmental analyses of wing pattern formation. We propose future analyses of character evolution accommodate conflicting phylogenetic estimates by explicitly testing alternative evolutionary hypotheses.