The evolutionary diversity of insect retinal mosaics: common design principles and emerging molecular logic

• Insect retinas contain homologous building blocks.
• The stochastic retinal mosaics of different insects bear striking similarities.
• Insect retinas contain localized specializations with defined functions.
• Regional differences in the retinal mosaic have behavioral consequences.
• Retinal bands and stripes are poorly understood emerging design challenges.

Independent evolution has resulted in a vast diversity of eyes. Despite the lack of a common Bauplan or ancestral structure, similar developmental strategies are used. For instance, different classes of photoreceptor cells (PRs) are distributed stochastically and/or localized in different regions of the retina. Here, we focus on recent progress made towards understanding the molecular principles behind patterning retinal mosaics of insects, one of the most diverse groups of animals adapted to life on land, in the air, under water, or on the water surface. Morphological, physiological, and behavioral studies from many species provide detailed descriptions of the vast variation in retinal design and function. By integrating this knowledge with recent progress in the characterization of insect Rhodopsins as well as insight from the model organism Drosophila melanogaster, we seek to identify the molecular logic behind the adaptation of retinal mosaics to the habitat and way of life of an animal.