Morphological and Spatial Diversity of the Discal Spot on the Hindwings of Nymphalid Butterflies: Revision of the Nymphalid Groundplan.

Joji M Otaki

doi:10.3390/insects11100654

Abstract

Simple SummaryButterfly wing color patterns are diverse, but they can be understood as modifications of the common scheme called the nymphalid groundplan. The discal spot is relatively small, but it is one of the important components of the nymphalid groundplan. Using many hindwing specimens of the family Nymphalidae, the morphological and spatial diversity of the discal spot was studied. The discal spot is expressed as a small or narrow spot, a pair of parallel bands, a diamond or oval structure, a large dark spot, a few fragmented spots, or a white structure. The discal spot is always located in a central portion of the wing defined by the wing veins, and this portion is sandwiched by a pair of bands of the central symmetry system, another important component of the nymphalid groundplan. On the basis of these results, the present study revises the nymphalid groundplan in minor points; the discal spot is an independent and diverse miniature symmetry system nested within the central symmetry system. Due to the involvement of wing veins to define the locations of the discal spot, the present study suggests the possible developmental dynamics of butterfly color pattern formation that produces color pattern diversity.Diverse butterfly wing color patterns are understood through the nymphalid groundplan, which mainly consists of central, border, and basal symmetry systems and a discal spot. However, the status of the discal spot remains unexplored. Here, the morphological and spatial diversity of the discal spot was studied in nymphalid hindwings. The discal spot is expressed as a small or narrow spot, a pair of parallel bands, a diamond or oval structure, a large dark spot, a few fragmented spots, or a white structure. In some cases, the discal spot is morphologically similar to and integrated with the central symmetry system (CSS). The discal spot is always located in a distal portion of the discal cell defined by the wing veins, which is sandwiched by the distal and proximal bands of the CSS (dBC and pBC) and is rarely occupied by border ocelli. The CSS occasionally has the central band (cBC), which differs from the discal spot. These results suggest that the discal spot is an independent and diverse miniature symmetry system nested within the CSS and that the locations of the discal spot and the CSS are determined by the wing veins at the early stage of wing development.

Highlights

Insects have a large variety of morphological structures and color patterns
Color patterns on butterfly wings are very diverse. They are so diverse that they have attracted the attention of biologists who are interested in pattern formation and morphogenesis
Simple Spot or Line on the Discal Cross Vein and Its Extension In Catacroptera cloanthe (Figure 3a), the discal cross vein is not present, but the discal spot is present as an isolated single spot on the expected location where the discal cross vein is supposed to be located as an extension of the wing vein CuA1

Summary

Introduction

Insects have a large variety of morphological structures and color patterns. Color patterns on butterfly wings are very diverse. They are so diverse that they have attracted the attention of biologists who are interested in pattern formation and morphogenesis. Some researchers have searched for a unified understanding of the diversity of butterfly wing color patterns. As early as Insects 2020, 11, 654; doi:10.3390/insects11100654 www.mdpi.com/journal/insects. 22 of of 23 searched for a unified understanding of the diversity of butterfly wing color patterns. As early as Spemann and and Mangold

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