The role of wing veins in colour pattern development in the butterfly Papilio xuthus (Lepidoptera: Papilionidae)

Paul Bernhardt Koch,H Frederik Nijhout

doi:10.14411/eje.2002.012

Abstract

Naturally occurring veinless specimen of the swallowtail Papilio xuthus show an extremely aberrant colour pattern. In spite of the fact that we have no breeding data, these veinless specimen are provisionally called veins-reduced mutant. In these mutants seven longitudinal veins of the fore wing and five of the hind wing are absent. The absence of wing veins is associated with a loss of the broad black venous stripes that normally are present along the proximal portion of the veins. In addition, missing veins cause a loss of the dislocation of black bands in adjacent wing cells, so that what are discrete black segments in normal wings become continuous bands in the veinless wing. Computer simulations show that the morphology of the striped patterns on both the veinless and veined wing can be explained if the wing margin acts as an inductive source of pattern formation and the veins act simply as boundaries to the propagation of the signal from the wing margin. The vein-dependent patterns by contrast, require that the veins act as inductive sources, at least along their proximal portion. This dual role of wing veins is consistent with prior observations on the biology of colour pattern formation. The unique veinless colour pattern strongly supports the hypothesis that the wing margin is the dominant organiser of colour pattern in this species, and possibly in other Papilionidae.

Highlights

Wing colour patterns provide a rich source of material for comparative investigations of the principles of pattern development
Computer simulations show that the morphology of the striped patterns on both the veinless and veined wing can be explained if the wing margin acts as an inductive source of pattern formation and the veins act as boundaries to the propagation of the signal from the wing margin
The nymphalid groundplan suggests that wing patterns are composed of three sets of paired pig ment bands, the symmetry systems, that run from the anterior to the posterior margin of the wing and called respectively, the basal, central, and border-symmetry systems

Summary

Introduction

Wing colour patterns provide a rich source of material for comparative investigations of the principles of pattern development. Comparative analyses revealed that there is a general underlying principle of colour pattern organisation in butterflies, named the “nymphalid ground plan”, because it can be used to explain the structure and diversity of wing patterns in the family Nymphalidae (Schwanwitsch, 1924; Süffert, 1927; Nijhout, 1991). In many colour patterns these pig ment bands typically have discontinuities or dislocations where they cross a wing vein. The reason for these dislo cations is that pattern determination in each wing-cell (a wing-cell is the area bounded by wing veins) is partially uncoupled from pattern determination in adjoining wing cells. The wing veins appear to act as barriers to the propagation of determinative signals so that in each wing cell the processes of pattern formation become semi independent: they obey common genetic rules but are causally uncoupled from each other, much like left and right sides of a bilaterally symmetrical organism are uncoupled from each other

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