Color‐pattern analysis of parafocal elements in butterfly wings

Butterfly wing color‐patterns are composed of anatomically identifiable pattern elements, whose positional relations are idealized in the “nymphalid groundplan”. But the status of the parafocal element and submarginal band (which are collectively called “the peripheral elements” for convenience) in this groundplan has been ambiguous. Herein, I descriptively analyze homologous color‐patterns of the parafocal elements in the representative nymphalid butterflies. Cases are presented where the distal and proximal peripheral elements are symmetric on the eyespot focal axis, they are continuous around eyespots, and a given parafocal element shows a concentric pattern. Multi‐compartmental comparison of the consecutive parafocal elements on a given wing surface indicates that the relative locations of the parafocal elements can correlate with the eyespot size and that a peripheral part of an eyespot can be “disconnected” from its focal part. These cases suggest the fundamental difficulty in unequivocally distinguishing the parafocal element from the eyespot at least in some nymphalid species. Taken together, it appears that the parafocal element is developmentally regulated by the organizing activity of the prospective eyespot focus, and thus they are to be considered as a part of the border symmetry system. However, the parafocal element also seems to be organized by its own focus that acts as the secondary organizing center at least in some species. These conclusions based on the natural color‐patterns are in good agreement with those based on the physiologically‐induced color‐pattern changes.