Abstract
Butterfly wing color patterns often contain eyespots, which are developmentally determined at the late larval and early pupal stages by organizing activities of focal cells that can later form eyespot foci. In the pupal stage, the focal position of a future eyespot is often marked by a focal spot, one of the pupal cuticle spots, on the pupal surface. Here, we examined the possible relationships of the pupal focal spots with the underneath pupal wing tissues and with the adult wing eyespots using Junonia butterflies. Large pupal focal spots were found in two species with large adult eyespots, J. orithya and J. almana, whereas only small pupal focal spots were found in a species with small adult eyespots, J. hedonia. The size of five pupal focal spots on a single wing was correlated with the size of the corresponding adult eyespots in J. orithya. A pupal focal spot was a three-dimensional bulge of cuticle surface, and the underside of the major pupal focal spot exhibited a hollowed cuticle in a pupal case. Cross sections of a pupal wing revealed that the cuticle layer shows a curvature at a focal spot, and a positional correlation was observed between the cuticle layer thickness and its corresponding cell layer thickness. Adult major eyespots of J. orithya and J. almana exhibited surface elevations and depressions that approximately correspond to the coloration within an eyespot. Our results suggest that a pupal focal spot is produced by the organizing activity of focal cells underneath the focal spot. Probably because the focal cell layer immediately underneath a focal spot is thicker than that of its surrounding areas, eyespots of adult butterfly wings are three-dimensionally constructed. The color-height relationship in adult eyespots might have an implication in the developmental signaling for determining the eyespot color patterns.
Highlights
Wing color patterns are highly diverse, but it has been thought that they mostly derive from the nymphalid ground plan [1,2,3,4,5]
We have developed a method for real-time in vivo imaging for pupal wing tissues [17,19,20,21]
The large focal spots were found in the species with large eyespots in the adult wings, J. orithya and J. almana
Summary
Wing color patterns are highly diverse, but it has been thought that they mostly derive from the nymphalid ground plan [1,2,3,4,5]. The nymphalid ground plan is composed of three major symmetry systems and two peripheral systems [1,2,3,4,5]. Pupal Cuticle Spots in Junonia Butterflies composed of a core element at the center and a pair of paracore elements at both sides of a core element [4]. The prospective eyespot focus at the early pupal stage functions as an organizer for the eyespot color pattern determination as demonstrated by physical damage and transplantation experiments [6,7,8,9,10,11]
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