Microspectrophotometry of visual pigments and oil droplets in a marine bird, the wedge-tailed shearwaterPuffinus pacificus: topographic variations in photoreceptor spectral characteristics

Abstract

SUMMARY Microspectrophotometric examination of the retina of a procellariiform marine bird, the wedge-tailed shearwater Puffinus pacificus, revealed the presence of five different types of vitamin A1-based visual pigment in seven different types of photoreceptor. A single class of rod contained a medium-wavelength sensitive visual pigment with a wavelength of maximum absorbance (λmax) at 502 nm. Four different types of single cone contained visual pigments maximally sensitive in either the violet(VS, λmax 406 nm), short (SWS, λmax 450 nm), medium (MWS, λmax 503 nm) or long (LWS,λ max 566 nm) spectral ranges. In the peripheral retina, the SWS, MWS and LWS single cones contained pigmented oil droplets in their inner segments with cut-off wavelengths (λcut) at 445 (C-type),506 (Y-type) and 562 nm (R-type), respectively. The VS visual pigment was paired with a transparent (T-type) oil droplet that displayed no significant absorption above at least 370 nm. Both the principal and accessory members of the double cone pair contained the same 566 nm λmax visual pigment as the LWS single cones but only the principal member contained an oil droplet, which had a λcut at 413 nm. The retina had a horizontal band or `visual streak' of increased photoreceptor density running across the retina approximately 1.5 mm dorsal to the top of the pecten. Cones in the centre of the horizontal streak were smaller and had oil droplets that were either transparent/colourless or much less pigmented than at the periphery. It is proposed that the reduction in cone oil droplet pigmentation in retinal areas associated with high visual acuity is an adaptation to compensate for the reduced photon capture ability of the narrower photoreceptors found there. Measurements of the spectral transmittance of the ocular media reveal that wavelengths down to at least 300 nm would be transmitted to the retina.

Mimicry, colour forms and spectral sensitivity of the bluestriped fangblenny,Plagiotremus rhinorhynchos

“…Absorbance spectra (350-800 nm) of individual rod and cone outer segments were measured using a computercontrolled, single-beam, wavelength-scanning microspectrometer as described in detail elsewhere (Hart 2004). Each pre-bleach absorbance spectrum consisted of a sample scan of the outer segment and a baseline scan of a cell-free area of the preparation adjacent to the outer segment.…”

Cone photoreceptor oil droplet pigmentation is affected by ambient light intensity

“…Transverse absorptance spectra (330-800·nm) of cone photoreceptor oil droplets were made using a computercontrolled, single-beam, wavelength-scanning microspectro-N. S. Hart, T. J. Lisney and S. P. Collin photometer (MSP) described in detail elsewhere (Hart, 2004). A sample scan was made by aligning the measuring beam (dimensions 131·mm) within an oil droplet and recording the amount of light transmitted at each wavelength across the spectrum.…”

“…The relative quantal spectral sensitivity of the outer segments of the SWS, MWS and LWS single cones and the principal member of the LWS double cones in the ventral retina of the bright-light and dim-light groups was modelled as described previously (Hart, 2002;Hart, 2004;Hart and Vorobyev, 2005). Cone outer segment absorptance was modelled using the rhodopsin (vitamin A 1 -based) visual pigment templates of Govardovskii et al (Govardovskii et al, 2000), a specific (decadic) absorbance of 0.014·mm -1 (Bowmaker and Knowles, 1977) and a cone outer segment length of 16·mm (Morris and Shorey, 1967).…”

Visual pigments in a palaeognath bird, the emuDromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision

“…Transverse absorbance spectra (330-800 nm) of individual photoreceptor outer segments and oil droplets were measured using a single-beam wavelength-scanning microspectrophotometer [13] and analysed using established methods [14].…”