Insect interordinal relationships: Evidence from the visual system

Abstract

Insects are by far the most speciose and also one of the most intensively studied animal groups on earth. To contribute to a recent effort in reviewing and revalidating morphological and molecular data sets for the reconstruction of insect interordinal phylogeny, we turned our attention to structural and ontogenetic traits of the visual system. Discussed is a suite of characters, nine of which are proposed to show phylogenetically informative differences between insect orders. Of these, three (second mitotic wave, retina blood border, indirect ocellus innervation) relate to basal diversifi cation events in the Pterygota. Four character states represent autapomorphies of the Endopterygota (optic lobe invagination, possession of stemma, stemmata derived adult brain photoreceptors, and postembryonic progressive eye development). Lastly, the spatially undissociated lobula plate in hymenopteran representatives like honey bee, which contrasts with the well separated lobula plate in other endopterygotan orders, is discussed as possibly indicating a basal position of the Hymenoptera in the Endopterygota.