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First published online November 17, 2006
Journal of Experimental Biology 209, 4776-4787 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02568

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Cone photoreceptor oil droplet pigmentation is affected by ambient light intensity

Nathan S. Hart^*, Thomas J. Lisney and Shaun P. Collin

Vision, Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia

View larger version (15K): [in a new window]   Fig. 1. (A) Semi-logarithmic plot of habitat spectral irradiance (350-800 nm) for the different light treatments employed in the study. `BRIGHT' refers to the unshaded cage (`bright-light') treatment, `DIM' refers to the shaded cage (`dim-light') treatment. The subscripts `Downwelling' and `Upwelling' refer to irradiance measurements made with the recording probe pointing either directly upwards towards the sky or directly downwards towards the substrate, respectively. (B) Ratios of downwelling (solid line) and upwelling (broken line) spectral irradiance between the bright-light and dim-light treatment groups.

View larger version (25K): [in a new window]   Fig. 2. Mean absorptance spectra of pigmented cone oil droplets in 33-week-old chickens measured using microspectrophotometry. Panels correspond to oil droplets measured in the dorsal (A) and ventral (B) retina of a chicken reared in dim light and the dorsal (C) and ventral (D) retina of a chicken reared in bright light. C, Y, R and P refer to the oil droplets found in the short-(SWS), medium-(MWS) and long-wavelength-sensitive (LWS) single cones and the principal member of the LWS double cones, respectively. Note the difference in spectra between light-treatment groups, especially with respect to the Y-, R- and P-type oil droplets, and also between dorsal and ventral retina locations within the same bird. Each spectrum is the average of the individual spectra from 10 different oil droplets of a given oil-droplet type.

View larger version (47K): [in a new window]   Fig. 3. Variations in cut-off wavelength (cut) of the different pigmented cone oil droplets in the dorsal and ventral retina as a function of the type and duration of light treatment. Solid line, `bright-light' group; broken line, `dim-light' group. Bars around data points represent ±1 s.d. for the mean value (N=10). Panels A-D show data for C-, Y-, R- and P-type oil droplets located in the dorsal retina and panels E-H show data for the same droplet types located in the ventral retina. The earliest microspectrophotometric data were obtained after 6 weeks of exposure to the different lighting conditions, i.e. when the chickens were 10 weeks old. Chickens reach sexual maturity between 18 and 24 weeks of age and the state of maturity is indicated on each graph, with the border between juvenile and adult status taken as the midpoint of this range (i.e. 21 weeks of age), which occurred 17 weeks after the onset of the different light treatments.

View larger version (19K): [in a new window]   Fig. 4. Calculated relative quantal spectral sensitivity functions for the outer segment of cones containing pigmented oil droplets in 33-week-old adult chickens reared in bright (solid line) or dim (broken line) light. (A) C-type oil droplets in the short-wavelength-sensitive single cones; (B) Y-type oil droplets in the medium-wavelength-sensitive single cones; (C) R-type oil droplets in the long-wavelength-sensitive (LWS) single cones and (D) P-type oil droplets in the principal member of the LWS double cones. Note the increased sensitivity and spectral bandwidth of all cone types in the dim-light group, owing to the reduced density of carotenoid pigments in their respective oil droplet types, compared with that of the bright-light group (see Figs 2, 3).