Developmental shifts in eye morphology and visual ecology of banded flower mantis (Theopropus elegans)

Compound eyes display high morphological diversity across arthropods, including rare cone-shaped forms whose visual function is puzzling because their unusual shape seems to defy expectations of how eyes sample visual space. Species in which eye shape changes through development offer a valuable opportunity to investigate how cone-shaped morphology affects visual sampling and acuity. In this study, we investigated the developmental trajectory of eye morphology in the banded flower mantis (Theopropus elegans), a species that transitions from a cone-shaped to a spherical eye during growth. Using micro-computed tomography, we measured changes in binocular overlap, ommatidium number, eye volume, facet size and spatial acuity across instars. Early instar nymphs exhibit high vertical acuity with two distinct vertical acute zones. While vertical acuity remains stable throughout development, ommatidium number, eye size, facet size and horizontal acuity increase significantly as the eyes become more spherical. A horn-like protrusion, lacking ommatidia, projects from the tip of the cone-shaped eye, creating a dorsal blind spot. This structure, common in mantises with cone-shaped eyes, likely enhances camouflage by disrupting the outline of the eye. These findings demonstrate how ontogenetic changes in eye shape are associated with shifts in visual performance and ecological strategy in praying mantises.