Abstract
BackgroundButterfly and moth eyespots can share a similar appearance, involving multiple concentric rings of colored scales, but usually occuring in non-homologous positions on the wing. Within the butterflies, on the other hand, spots that share the same homologous position may not share the concentric ring structure; and, in butterfly species that have eyespots with concentric rings, ectopic eyespots with a similar ring structure can be induced by means of a simple epidermal wound. The extent to which all these eyespots, natural or induced, share similar genes and developmental mechanisms is investigated here by means of protein in-situ localizations in selected butterfly and moth species. In addition to looking at some of the transcription factors previously identified as being involved in eyespot formation, we also tested the involvement of candidate genes from the Wingless and TGF-β signaling pathways as putative morphogens for eyespot development.ResultsSaturniid moth and nymphalid butterfly eyespots with concentric rings of color express at least two transcription factors, Distal-less and Engrailed, in the center of the future pattern. Nymphalid eyespots centers also express the ligand Wingless and an activated signal transducer, a phosphorylated Smad protein, but neither these proteins nor the previous two proteins are found in pierid spot centers, which consist of a single patch of color. Both butterfly wing patterns, however, express a third transcription factor, Spalt, a portion of whose expression domain maps to the black scales on the adult wing. Wounding a nymphalid wing, on the other hand, leads to upregulation of Distal-less, engrailed and spalt in subsets of cells around the wounding site, mimicking concentric eyespot development.ConclusionWingless and TGF-β ligands are both candidate morphogens involved in nymphalid butterfly eyespot formation. These eyespots, as well as saturniid moth eyespots with concentric circles, share two genes that are associated with the differentiation of the signaling cells in nymphalid eyespots. This commonality suggests that they may be produced via the same developmental mechanism despite their non-homologous location. By contrast, pierid butterfly spots of a single color share some of the same genes but appear to be produced by a different mechanism. Eyespots with concentric rings may have co-opted a wound healing genetic network during their evolution.
Highlights
And moth eyespots can share a similar appearance, involving multiple concentric rings of colored scales, but usually occuring in non-homologous positions on the wing
The timing of wg expression varied slightly from individual to individual with expression first visualized in the eyespot centers at 10.5 h after pupation and present until 16 h after pupation (Fig. 3)
Fspiaglut reexp4ression in Bicyclus anynana larval and pupal wings spalt expression in Bicyclus anynana larval and pupal wings. (A) sal is expressed in the future eyespot centers, in the late 5th instar larval hindwing discs (50×); (B) sal expression extends to the scale-building cells in a larger circular pattern around the densely packed cells of the eyespot focus, at 19 h after pupation (200×)
Summary
And moth eyespots can share a similar appearance, involving multiple concentric rings of colored scales, but usually occuring in non-homologous positions on the wing. Pattern elements consisting of one or more concentric rings of colored scales, the eyespots, can occur at different positions in the wing in different lineages and display different morphologies and, make intriguing subjects for investigating questions of homology [1]. When eyespots appear in moth lineages they are usually found as a single element in each wing surface, straddling a cross vein in the center of the wing These are called the discal-cell eyespots [2]. In members of the superfamilies Bombycoidea, Drepanoidea and Geometrodeia, which are closely related to the butterfly superfamily Papilionoidea, eyespots appear along the border of the wing, in the space between two veins [3]. The extent to which discal-cell eyespots are homologous to border eyespots and to which single colored spots are homologous to eyespots with concentric rings remain largely unknown and is here the focus of our investigation
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