Deep conservation complemented by novelty and innovation in the insect eye ground plan

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Entomology

Background:

• Insect compound eyes exhibit remarkable diversity in form and function.
• The underlying genetic mechanisms and developmental patterning of insect eyes across different species remain largely unknown.

Purpose of the Study:

• To investigate whether distant insect species utilize similar or different mechanisms for eye patterning.
• To identify the genetic changes responsible for the diversity in insect eye form and function.

Main Methods:

• Comparative analysis of transcription factor expression (Prospero, Spalt, Defective proventriculus) to establish photoreceptor homology.
• Gene knockout (CRISPR/Cas9) and knockdown (RNAi) experiments in various insect species (houseflies, butterflies, crickets, beetles).
• Examination of conserved signaling pathways (EGFR, Sevenless) in retina development.

Main Results:

• Homologous developmental programs pattern retinas across diverse insect species, including flies, mosquitos, butterflies, moths, beetles, wasps, honeybees, and crickets.
• Specific transcription factors (Pros, Sal, Dve) mark homologous photoreceptor types.
• EGFR and Sevenless signaling pathways are crucial for photoreceptor recruitment, with variations in reliance across species.
• A conserved "insect eye ground plan" exists during early ommatidia patterning, preceding species-specific modifications.

Conclusions:

• Retina development in insects follows a highly conserved phylotypic stage, suggesting an ancient "insect eye ground plan."
• Diversification of insect eyes arises from modifications to this ground plan, including ground plan modification, nonstochastic patterns, and specialized regions.
• Developmental divergence after establishing the ground plan accounts for the vast diversity in insect visual systems.