Wing pattern formation in Lepidoptera: A model
A formal model is presented that demonstrates how the color patterns of the wings of butterflies and moths can be analysed in terms of current concepts of pattern formation. A review of pertinent literature on this little‐known developmental system is provided. Crucial to the understanding of color pattern formation in lepidopteran wings is the realization that the wing pattern is a mosaic. The pattern in each wing cell (i.e., the area bordered by wing veins) is determined independently from the pattern in other cells. Within a cell, pigments are deposited in a definite relation to a central focus. A focus always lies on the cell midline and is often visible as a small pigmented dot. In the simplest condition the color pattern is laid down around a focus as a system of perfect concentric circles (eyespots). More often these circles are considerably distorted and have an axis of bilateral symmetry that parallels the wing veins. The nature and extent of these distortions from circularity account, to a large degree, for the species‐specific character of the wing pattern. The determination of such patterns is most readily explained if it is assumed that a focus represents the reference point with respect to which positional information (for pigment deposition) is specified. Circular patterns are thus obtained if all points equidistant from a focus undergo identical differentiation. Deviations from circularity of the pattern around a focus indicate that either the specification or interpretation of positional information is not the same in all areas around a focus. This phenomenon is most conveniently described as an “interpretation landscape”: a gradient system whose value at any point in a morphogenetic field is a measure of how positional information is to be interpreted at that location. Examples are provided of how species‐specific wing patterns can be generated by modest alterations in the shape of the interpretation landscape. As a rule the field of a focus is limited by the margins of the wing cell in which it is centered except in cases where no focus is present in an adjacent cell. Under those circumstances one focus can determine the pattern in several adjoining wing cells. Copyright © 1978 Wiley‐Liss, Inc., A Wiley Company
