Ultraviolet photopigment sensitivity and ocular media transmittance in gulls, with an evolutionary perspective

Gulls (Laridae excluding Sternidae) appear to be the only shorebirds (Charadriiformes) that have a short wavelength sensitive type 1 (SWS1) cone pigment opsin tuned to ultraviolet (UV) instead of violet. However, the apparent UV-sensitivity has only been inferred indirectly, via the interpretation that the presence of cysteine at the key amino acid position 90 in the SWS1 opsin confers UV sensitivity. Unless the cornea and the lens efficiently transmit UV to the retina, gulls might in effect be similar to violet-sensitive birds in spectral sensitivity even if they have an ultraviolet sensitive (UVS) SWS1 visual pigment. We report that the spectral transmission of the cornea and lens of great black-backed Larus marinus and herring gulls L. argentatus allow UV-sensitivity, having a lambda(T0.5) value, 344 nm, similar to the ocular media of UV sensitive birds. By molecular sequencing of the second alpha-helical transmembrane region of the SWS1 opsin gene we could also infer that 15 herring gulls and 16 yellow-legged gulls L. michahellis, all base-pair identical, are genetically UV-sensitive.