A spectacular diversity of forms and features allow species to thrive in different environments, yet some structures remain relatively unchanged. Insect compound eyes are easily recognizable despite dramatic differences in visual abilities across species.It is unknown whether distant insect species use similar/different mechanisms to pattern their eyes or what types of genetic changes produce diversity of form and function. We find that flies, mosquitos, butterflies, moths, beetles, wasps, honeybees, and crickets use homologous developmental programs to pattern their retinas. The TFs Prospero (R7), Spalt (R7+R8), and Dve (R1-6) can be used to establish photoreceptor (PR) homology across the insects, and can be used to visualize developmental stages during PR recruitment. Next, we used gene knockout (CRISPR/Cas9) in house flies, butterflies, and crickets and gene knockdown (RNAi) in beetles and find that EGFR and RTK signaling pathways are required to recruit motion and color vision PRs across the insects, though we find that Drosophila have a decreased reliance on RTK signaling relative to other insects. Despite the incredible morphological variation of eyes found in different species, retina development passes through a highly conserved phylotypic stage when the unit eyes (ommatidia) are first patterned. This ancient patterning process likely represents an “insect eye ground plan” that is rarely modified. We then identify three main types of developmental patterning modifications that allow for the functional diversification of insect eyes. We suggest that developmental divergence after the ground plan is established is responsible for the incredible diversity observed across insect visual systems.
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