Evolution of insect eye development: first insights from fruit fly, grasshopper and flour beetle.

The molecular genetic dissection of Drosophila eye development led to the exciting discovery of a surprisingly large panel of genes and gene activities, which are functionally conserved across phyla. Little effort has yet been made towards pinpointing non-conserved gene functions in the developing Drosophila eye. This neglects the fact that Drosophila visual system development is a highly derived process. The comparative analysis of Drosophila eye development within insects can be expected to enhance resolution and accuracy of between phyla comparisons of eye development, and to reveal molecular developmental changes that facilitated the evolutionary transition from hemimetabolous to holometabolous insect development. Here we review aspects of early Drosophila eye development, which are likely to have diverged from the situation in more primitive insects, as indicated by results from work in the flour beetle Tribolium castaneum and the grasshopper Schistocerca americana.