FRIEDRICH, Markus; Wayne State University, Detroit: From lobes to discs: evolution of insect eye development

Virtually everything we know about insect eye development has been gained from studying the molecular genetic workhorse Drosophila melanogaster. A large number of eye developmental genes have been identified in the fruitfly, many of which are functionally conserved across phyla. This is particularly striking considering that the ontogeny of the Drosophila visual system is evolutionarily highly derived. Drosophila is a holometabolous insect, which undergoes complete metamorphosis. From the egg hatches a highly derived larva, which lacks a head capsule and external eyes and instead possesses a pair of specialized larval eyes. The precursor tissue of the adult retina and head cuticle is set aside during embryogenesis in the form of imaginal discs which differentiate during late larval and pupal development. Timing and spatial control of eye development is very different in the more primitive ametabolous and hemimetabolous insects. In this case, a substantial part the adult eye forms during embryogenesis from the eye lobe compartments of the embryonic head. The first immature instars hatch with a fully elaborated head, which is maintained into the adult instar thus representing a miniature blueprint of the adult head. The dramatic differences between embryonic eye development in primitive insects and postembryonic eye development in Drosophila must extend to the genetic regulatory level. Recent data from our laboratory on the role of wingless, decapentaplegic and ecdysone signaling during embryonic eye development in the hemimetabolous grasshopper Schistocerca americana support this hypothesis. I will review the molecular genetics of Drosophila eye development discussing the evolutionary divergence from the situation in primitive insects.