Das, Debipriya; (1997) Visual pigments, oil droplets and opsin sequences from the canary, Serinus Canaria. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The visual receptors in the retina of the passeriform bird Serinus canaria (the canary) have been examined microspectrophotometrically. The rods have a maximum absorbance close to 500 nm. Four spectrally different classes of single cone are also present: a long-wave sensitive cone with a photopigment P567, a middle-wave sensitive cone with a P501, a short-wave sensitive cone with a P442, and an ultraviolet sensitive cone with a P366. Also present are double cones possessing the P567 in both principal and accessory members. Typical combinations of photopigment and oil droplet occur in most cone classes, for instance, the MWS cones are paired with a Y-type droplet with a cut-off at 506 nm, SWS cones are paired with a C-type droplet with maximum absorbance below 410 nm and the UV cones contain a fully transparent oil droplet. In the double cones a pale droplet with variable absorbance (peaking at 410-415 nm) is associated with the principal member whereas the ellipsoid region of the accessory member contains only low concentrations of carotenoid. An ambiguity exists in the nature of the oil droplet found in the single LWS cone class; in some birds, LWS cones are paired with a typical R-type droplet with a cut-off at 578 nm, however the majority of canaries do not appear to possess R-type droplets. In most birds the LWS pigment is invariably paired with the P-type droplet which has previously been associated exclusively with the principal member of the double cone. The visual pigment genes coding for all five canary opsins have also been isolated and sequenced and complement the spectral classes identified from MSP. From these DNA sequences, it has been possible to deduce the unique amino acid sequence of each of the opsin proteins and to identify putative spectral tuning sites.

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