Meeting Abstract
Chitons are marine mollusks protected by eight over-lapping shell plates. In most species, numerous sensory organs – known as aesthetes – are embedded in these shell plates. Aesthetes come in a variety of forms, ranging from non-pigmented sensory cells, to pigmented clusters of cells, to image-forming eyes with lenses made of shell material. Chitons are a promising system for the study of eye evolution because their eyes may be the most recently evolved of any animal. The fossil record of chitons extends back to the Cambrian, but chitons with eyes have only diversified within the last 25 million years. Further, chitons display multiple light-influenced behaviors that are simple, stereotyped, and easily-manipulated in the laboratory. Through transcriptome sequencing, we find that the aesthetes of chitons tend to express molecular components consistent with multiple types of phototransduction. Using immunohistochemistry, we find that the aesthetes, but not the eyes, of the chiton Acanthopleura granulata express molecular components of phototransduction (r-opsin, Gq alpha, and the ion channel TRP) that are similar to those expressed by the cephalic eyes of many invertebrates. The eyes of Acanthopleura granulata, however, may operate via a separate phototransduction pathway initiated by a distantly-related family of opsins. Finally, we describe how we are using blockers of opsin and ion channel function to study the contribution of different molecular components to the light-influenced behaviors of chitons. We conclude that multiple phototransduction pathways tend to be associated with the aesthetes of chitons and that the eyes of chitons may have evolved from the aesthetes of eyeless ancestors.
