Meeting Abstract
Pancrustacea offer great opportunities to investigate the evolutionary history of vision because of a diversity of eye designs and life styles. Their most prominent photosensitive organs, two compound eyes, consist of individual photoreception units called ommatidia. Compound eyes can be split in dorsal and ventral halves, be disintegrated to few, loosely assembled ommatidia, transformed into camera-type eyes (lateral ocelli) or absent. The other main photosensitive organs of pancrustaceans are median eyes, named naupliar eyes in crustaceans and dorsal ocelli in insects. These three camera-type eyes are positioned dorso-frontally on the head and are sometimes joined together, partly reduced or absent. Homologies of pancrustacean eyes and photoreceptors have been inferred from morphological and developmental comparisons. On a finer time-scale, relationships can be resolved using opsin-based photopigments, the first components of the visual transduction cascade. Data on opsin phylogeny and expression pattern have accumulated in recent years, but there is a strong bias for the compound eyes of a few, derived taxa. In an attempt to draw general conclusions, I interpret results on both eye types in Orthoptera, a comparatively early branching insect lineage, in the context of data on other insect orders and crustaceans. The opsin phylogeny suggests that gene duplications, permitting differential opsin expression in insect ocelli and compound eyes, occurred independently more than once and recently compared to the origin of the eyes. While expression patterns in the compound eyes of two cricket species are strikingly similar, they differ from those in a locust and other insects. This illustrates that a connection between specific photoreceptors and opsin families in pancrustaceans exists, but switches allowing for functional adaptations can be observed regularly.
