Meeting Abstract
Unlike other crustaceans, copepods lack compound eyes, depending on a frontal (nauplius) eye for vision. While naupliar eye photoreceptors have been characterized morphologically, little is known about the phototransduction cascade of this type of eye. Here, transcriptomics were used to identify candidate opsins in twelve taxonomically diverse copepod species. Within this high diversity of opsins, two major clades were observed in all species investigated: r-type middle wavelength sensitive opsins, and c-type pteropsins. There is additional evidence from a few species for the expression of several other types of opsins; long-wavelength sensitive r-type (harpacticoids only), tetraopsins, Rh7 opsins, and arthropsins. Several of these opsin types may be extraocular, including the pteropsins and tetraopsins, while the r-type middle- and long-wavelength sensitive opsins are likely used in the naupliar eyes. Main components for the visual pathway of the phototransduction cascade were also identified, including trp channels, arrestins, Gqα subunits, phospholipase C, and protein kinases. The copepod Calanus finmarchicus was observed to have ontogenic shifts in dominant opsin expression between naupliar and copepodite stages. The transcripts identified here provide a set of target genes for an analysis of the evolution of visual pigments present in the naupliar eyes copepods.
