Meeting Abstract

31.1  Sunday, Jan. 5 08:00  Uncovering patterns underlying the molecular evolution of non-visual photoreception in molluscs SERB, J.M.*; KRAUSE-PORATH, A.J.; PAIRETT, A.N.; Iowa State Univ. serb@iastate.edu

Photosensitivity of the dermis or extraocular photoreception (EOP) is widespread in animals. It has been suggested that this non-visual photoreception is the first step towards differentiated photoreceptive elements and, in some lineages, lead to the organization of these units into eyes capable of spatial vision. However, the data to support this evolutionary hypothesis is lacking. Often, the phototransduction pathway differs between dermal and ocular organs or the EOP mechanism varies between closely related taxa. This suggests that EOP does not result from a single ancestral condition, but may have polyphyletic origins. To examine this hypothesis, we compared photoreceptive systems from molluscan lineages and new phototransduction genes sequences from tissue-specific transcriptomes of the bivalve scallop (Pectinidae). We identified 10 opsin-like genes from these transcriptomes. We confirmed that a novel opsin is involved in scallop EOP by in situ hybridization. Amino acid comparison of EOP- and eye-specific opsins finds only 55% sequence identity despite being the same opsin type. These opsins also differ in secondary structure, ligand-binding site predictions, and tertiary structure models. To test the hypothesis that a gene duplication event resulted in tissue-specific functional divergence of scallop opsins, we compared all available molluscan opsins under a phylogenetic framework, which identified a gene duplication event leading to separate non-visual and spatial vision function in bivalves. From these data, we conclude that EOP has evolved multiple times across Mollusca. We hypothesize that EOP, like the eye, is an evolutionarily flexible system and has evolved though various molecular processes including co-option, gene sharing, and subfunctionalization of phototransduction pathway members.