Abstract
BackgroundDevelopmental studies on butterfly wing color patterns often focus on eyespots. A typical eyespot (such as that of Bicyclus anynana) has a few concentric rings of dark and light colors and a white spot (called a focus) at the center. The prospective eyespot center during the early pupal stage is known to act as an organizing center. It has often been assumed, according to gradient models for positional information, that a white spot in adult wings corresponds to an organizing center and that the size of the white spot indicates how active that organizing center was. However, there is no supporting evidence for these assumptions. To evaluate the feasibility of these assumptions in nymphalid butterflies, we studied the unique color patterns of Calisto tasajera (Nymphalidae, Satyrinae), which have not been analyzed before in the literature.ResultsIn the anterior forewing, one white spot was located at the center of an eyespot, but another white spot associated with either no or only a small eyespot was present in the adjacent compartment. The anterior hindwing contained two adjacent white spots not associated with eyespots, one of which showed a sparse pattern. The posterior hindwing contained two adjacent pear-shaped eyespots, and the white spots were located at the proximal side or even outside the eyespot bodies. The successive white spots within a single compartment along the midline in the posterior hindwing showed a possible trajectory of a positional determination process for the white spots. Several cases of focus-less eyespots in other nymphalid butterflies were also presented.ConclusionsThese results argue for the uncoupling of white spots from eyespot bodies, suggesting that an eyespot organizing center does not necessarily differentiate into a white spot and that a prospective white spot does not necessarily signify organizing activity for an eyespot. Incorporation of these results in future models for butterfly wing color pattern formation is encouraged.
Highlights
Developmental studies on butterfly wing color patterns often focus on eyespots
We focused on three wing regions of the ventral side that contain eyespots and/or white spots: the anterior forewing, the anterior hindwing, and the posterior hindwing (Fig. 1c)
The white spot (“focus”) of this eyespot was located in the M1 compartment, but this eyespot was not confined to the M1 compartment; it occupied two adjacent compartments, R5 and M2 (Fig. 2)
Summary
Developmental studies on butterfly wing color patterns often focus on eyespots. A typical eyespot (such as that of Bicyclus anynana) has a few concentric rings of dark and light colors and a white spot (called a focus) at the center. Lepidopteran insects are characterized by wings covered with scales and bristles These scales are variously colored, and a single scale serves as an image unit (or “pixel”). The border symmetry system is probably the most conspicuous in many nymphalid butterflies It is composed of a border ocellus (an eyespot) as a core element and a pair of parafocal elements (distal and proximal parafocal elements) as paracore elements (Nijhout 1991, 2001; Dhungel and Otaki 2009; Otaki 2009, 2012a). The white focal spot is often missing, and the various rings are often distorted differently in a single eyespot
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