Color Pattern on the Forewing of Micropterix (Lepidoptera: Micropterigidae): Insights into the Evolution of Wing Pattern and Wing Venation in Moths

Symmetry systems on the wings of Dichromodes Guenée (Lepidoptera: Geometridae) are unconstrained by venation

The nymphalid groundplan, an idealized schematic illustrating the essential elements of butterfly wing patterns, predicts a consistent relationship between color pattern and wing venation. Moths in the family Geometridae have wing shapes and patterns that often resemble those of butterflies, and until recently, this family was believed to be among butterflies’ closest relatives. However, an examination of the geometrid genus Dichromodes Guenée, 1858 shows no consistent relationship between the central symmetry system and wing venation. Whereas the distal edge of the central symmetry system is predicted to reach the costal margin proximal to the Subcostal vein in butterflies and acronictine moths, it has no consistent relationship with the Subcostal, Radius, or Radial Sector 1 veins in Dichromodes. This finding highlights developmental diversity that was previously overlooked due to the overwhelming preference for butterflies in studies of lepidopteran wing patterns.

Molecular mechanisms underlying simplification of venation patterns in holometabolous insects

How mechanisms of pattern formation evolve has remained a central research theme in the field of evolutionary and developmental biology. The mechanism of wing vein differentiation in Drosophila is a classic text-book example of pattern formation using a system of positional-information, yet very little is known about how species with a different number of veins pattern their wings, and how insect venation patterns evolved. Here, we examine the expression pattern of genes previously implicated in vein differentiation in Drosophila in two butterfly species with more complex venation Bicyclus anynana and Pieris canidia. We also test the function of some of these genes in B. anynana. We identify both conserved as well as new domains of decapentaplegic, engrailed, invected, spalt, optix, wingless, armadillo, blistered, and rhomboid gene expression in butterflies, and propose how the simplified venation in Drosophila might have evolved via loss of decapentaplegic, spalt and optix gene expression domains, silencing of vein inducing programs at Spalt-expression boundaries, and changes in gene expression of vein maintenance genes.

The wing pattern of Hydriomena Hübner, [1825] (Lepidoptera: Geometridae: Larentiinae) lacks a predictable relationship with venation

Two simple models have been successfully applied to predict the relationship between wing pattern and venation in various lineages of Lepidoptera. However, neither of these models holds for the geometrid genus Hydriomena Hübner, 1825. Wing patterns in Hydriomena were studied intensively during the 1920s after the description of the nymphalid groundplan, an idealized schematic that outlines the primary elements of butterfly wing patterns; geometrids strongly resemble butterflies and, until recently, were considered to be among their closest relatives. The evolution of wing pattern in Geometridae has been neglected since the 1930s. Here, the relationship between wing pattern and venation is examined for Hydriomena costipunctata Barnes and McDunnough, 1912 and the Hydriomena speciosata (Packard, 1873) group. These two lineages have some of the simplest wing patterns in Hydriomena, consisting of large, well-defined dark and light pattern elements. The relationship between wing pattern and venation varies considerably within and between these lineages and can even vary between the right and left wings on the same individual. Although many different wing patterns were observed among the individuals examined for this study, not one can be reconciled with either of the models that successfully predict the relationship between wing pattern and venation in many other groups of Lepidoptera. This suggests that bands occurring on the wings of Hydriomena are not homologous with those on the wings of butterflies or of Acronictinae (Macroheterocera: Noctuidae), the only other two obtectomeran lineages for which the relationship between wing pattern and venation has been examined in recent years.

Thin-film structural coloration from simple fused scales in moths

The metallic coloration of insects often originates from diverse nanostructures ranging from simple thin films to complex three-dimensional photonic crystals. In Lepidoptera, structural coloration is widely present and seems to be abundant in extant species. However, even some basal moths exhibit metallic coloration. Here, we have investigated the origin of the vivid metallic colours of the wing scales of the basal moth Micropterix aureatella by spectrophotometry and scanning electron microscopy. The metallic gold-, bronze- and purple-coloured scales share a similar anatomy formed of a fused lower and upper lamina resulting in a single thin film. The optical response of this thin-film scale can be attributed to thin-film interference of the incident light, resulting in the colour variations that correlate with film thickness. Subtle variations in the wing scale thickness result in large visible colour changes that give Micropterix moths their colourful wing patterns. This simple coloration mechanism could provide a hint to understand the evolution of structural coloration in Lepidoptera.

Fossil scales illuminate the early evolution of lepidopterans and structural colors

Lepidopteran scales exhibit remarkably complex ultrastructures, many of which produce structural colors that are the basis for diverse communication strategies. Little is known, however, about the early evolution of lepidopteran scales and their photonic structures. We report scale architectures from Jurassic Lepidoptera from the United Kingdom, Germany, Kazakhstan, and China and from Tarachoptera (a stem group of Amphiesmenoptera) from mid-Cretaceous Burmese amber. The Jurassic lepidopterans exhibit a type 1 bilayer scale vestiture: an upper layer of large fused cover scales and a lower layer of small fused ground scales. This scale arrangement, plus preserved herringbone ornamentation on the cover scale surface, is almost identical to those of some extant Micropterigidae. Critically, the fossil scale ultrastructures have periodicities measuring from 140 to 2000 nm and are therefore capable of scattering visible light, providing the earliest evidence of structural colors in the insect fossil record. Optical modeling confirms that diffraction-related scattering mechanisms dominate the photonic properties of the fossil cover scales, which would have displayed broadband metallic hues as in numerous extant Micropterigidae. The fossil tarachopteran scales exhibit a unique suite of characteristics, including small size, elongate-spatulate shape, ridged ornamentation, and irregular arrangement, providing novel insight into the early evolution of lepidopteran scales. Combined, our results provide the earliest evidence for structural coloration in fossil lepidopterans and support the hypothesis that fused wing scales and the type 1 bilayer covering are groundplan features of the group. Wing scales likely had deep origins in earlier amphiesmenopteran lineages before the appearance of the Lepidoptera.

The wing pattern of Moerarchis Durrant, 1914 (Lepidoptera: Tineidae) clarifies transitions between predictive models

The evolution of wing pattern in Lepidoptera is a popular area of inquiry but few studies have examined microlepidoptera, with fewer still focusing on intraspecific variation. The tineid genus Moerarchis Durrant, 1914 includes two species with high intraspecific variation of wing pattern. A subset of the specimens examined here provide, to my knowledge, the first examples of wing patterns that follow both the 'alternating wing-margin' and 'uniform wing-margin' models in different regions along the costa. These models can also be evaluated along the dorsum of Moerarchis, where a similar transition between the two models can be seen. Fusion of veins is shown not to effect wing pattern, in agreement with previous inferences that the plesiomorphic location of wing veins constrains the development of colour pattern. The significant correlation between wing length and number of wing pattern elements in Moerarchis australasiella shows that wing size can act as a major determinant of wing pattern complexity. Lastly, some M. australasiella specimens have wing patterns that conform entirely to the 'uniform wing-margin' model and contain more than six bands, providing new empirical insight into the century-old question of how wing venation constrains wing patterns with seven or more bands.

Phylogeny and Evolution of Lepidoptera

Until recently, deep-level phylogeny in Lepidoptera, the largest single radiation of plant-feeding insects, was very poorly understood. Over the past two decades, building on a preceding era of morphological cladistic studies, molecular data have yielded robust initial estimates of relationships both within and among the ∼43 superfamilies, with unsolved problems now yielding to much larger data sets from high-throughput sequencing. Here we summarize progress on lepidopteran phylogeny since 1975, emphasizing the superfamily level, and discuss some resulting advances in our understanding of lepidopteran evolution.

Variable wing venation in Agathiphaga (Lepidoptera: Agathiphagidae) is key to understanding the evolution of basal moths

Details of the ancestral groundplan of wing venation in moths remain uncertain, despite approximately a century of study. Here, we describe a 3-branched subcostal vein, a 5-branched medial vein and a 2-branched cubitus posterior vein on the forewing of Agathiphaga vitiensis Dumbleton 1952 from Vanuatu. Such veins had not previously been described in any Lepidoptera. Because wing veins are typically lost during lepidopteran evolutionary history, rarely-if ever-to be regained, the venation of A. vitiensis probably represents the ancestral character state for moths. Wing venation is often used to identify fossil insects as moths, because wing scales are not always preserved; the presence of a supposedly trichopteran 3-branched subcostal vein in crown Lepidoptera may decrease the certainty with which certain amphiesmenopteran fossils from the Mesozoic can be classified. And because plesiomorphic veins can influence the development of lepidopteran wing patterns even if not expressed in the adult wing, the veins described here may determine the location of wing pattern elements in many lepidopteran taxa.

Forewing color pattern in Micropterigidae (Insecta: Lepidoptera): homologies between contrast boundaries, and a revised hypothesis for the origin of symmetry systems

Background

Despite the great importance of lepidopteran wing patterns in various biological disciplines, homologies between wing pattern elements in different moth and butterfly lineages are still not understood. Among other reasons, this may be due to an incomplete understanding of the relationship between color pattern and wing venation; many individual wing pattern elements have a known relationship with venation, but a framework to unite all wing pattern elements with venation is lacking. Though plesiomorphic wing veins are known to influence color patterning even when not expressed in the adult wing, most studies of wing pattern evolution have focused on derived taxa with a reduced suite of wing veins.

Results

The present study aims to address this gap through an examination of Micropterigidae, a very early-diverged moth family in which all known plesiomorphic lepidopteran veins are expressed in the adult wing. The relationship between wing pattern and venation was examined in 66 species belonging to 9 genera. The relationship between venation and pattern element location, predicted based on moths in the family Tortricidae, holds for Sabatinca just as it does for Micropterix. However, the pattern elements that are lightly colored in Micropterix are dark in Sabatinca, and vice-versa. When plotted onto a hypothetical nymphalid wing in accordance with the relationship between pattern and venation discussed here, the wing pattern of Sabatinca doroxena very closely resembles the nymphalid groundplan.

Conclusions

The color difference in pattern elements between Micropterix and Sabatinca indicates that homologies exist among the contrast boundaries that divide wing pattern elements, and that color itself is not a reliable indicator of homology. The similarity between the wing pattern of Sabatinca doroxena and the nymphalid groundplan suggests that the nymphalid groundplan may have originated from a Sabatinca-like wing pattern subjected to changes in wing shape and reduced expression of venation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0687-z) contains supplementary material, which is available to authorized users.