Meeting Abstract
An important question in integrative biology is how and why complex structures, such as eyes, evolve. Chitons (Mollusca: Polyplacophora) provide a compelling system in which to study eye evolution, as extant taxa display a diversity of sensory structures embedded in their eight overlapping shell plates. These structures can include non-pigmented clusters of sensory cells (aesthetes), modified aesthetes that contain clusters of pigmented sensory cells (eyespots), and extrapigmented aesthetes that integrate an image-forming lens (eyes). Aesthetes are conserved among chitons. In addition to aesthetes, some chiton species have evolved eyespots or eyes. Here, we compare the expression of several molecular components of phototransduction in three species of chiton that represent each character state: Chaetopleura apiculata, a chiton with aesthetes, Chiton tuberculatus, a chiton with aesthetes and eyespots, and Acanthopleura granulata, a chiton with aesthetes and eyes. The aesthetes of each species express a diverse suite of G-protein alpha subunits, including Giα, Goα, Gqα, and Gsα. Aesthetes in each species also express rhabdomeric opsin (r-opsin) and transient receptor potential channel (TRP) proteins. Additionally, photoreceptor cells in the eyespots of C. tuberculatus express r-opsin, Goα, Gqα, and Gsα, and photoreceptor cells in the eyes of A. granulata express r-opsin, Gqα, and Gsα. Thus, we find that aesthetes, eyespots, and eyes express key components of rhabdomeric phototransduction, suggesting that these structures may detect light using this pathway. The expression of Giα, Goα, and Gsα in the aesthetes may indicate the presence of additional phototransduction pathways or the capability for multimodal sensory detection.
