Oxyopia Abstract
February 22, 2008
Friday, 4:00 PM
489 Minor Hall
Thomas Reuter, PhD
Professor Emeritus, Department of Biological and Environmental Sciences, University of Helsinki, Finland
Host: Dennis Levi
Title
Visualizing the effect of disruptions in the cone pigment genes on the organization of the cone mosaic
Abstract
The presentation discusses in general terms the conditions for chromatic vision at low light levels, and in more detail the effect of the bluish light and the low temperature on the color vision of seals and swordfish diving down to several hundred meters in clear ocean water.
At depths below 200 m the photon flux is very sparse, and furthermore limited to a bluish range with wavelengths between 400 nm and 500 nm. These are adverse conditions for color vision, and thus it is understandable that seals and whales foraging at 200 – 600 m depths have only one cone type, and no or very poor chromatic vision. Mammalian color vision is usually dichromatic and based on two cone types, absorbing around 545-560 nm and 400-450 nm, respectively. Seals and whales have lost their 400-450 nm cones, i.e., the blue-sensitive cones which potentially could be used in the mesopelagic zone. Thus it seems that whales and seals have completely given up photopic vision, i.e., cone vision, for their foraging below 200 m. In fact their retinae are markedly rod-dominated (Griebel and Peichl, 2003; Reuter and Peichl, 2008).
However, swordfish, marlins and tunas, also regularly foraging at 200-600 m depths, have, in addition to many rods, two cone types peaking at about 430 and 480 nm (Fritsches et al., 2003; Loew et al., 2002). These two cone types are thus perfectly suited for chromatic vision in the 420-490 nm zone: when the spectrum of an object is shifted towards shorter wavelengths (within this narrow spectral range) the stimulation of the 430 nm cone type increases, while it decreases for the 480 nm cone. Color vision is based on such shifts in relative cone stimulation. For the same reason human color discrimination is accurate in the yellow and blue-green regions. In the yellow region the relative stimulation of the "green" and "red" cones is changed, and in the blue-green region there is a rapid change in the stimulation of the "blue" and "green" cones.
Like other types of visual discrimination, color vision is a signal/noise discrimination, and thus chromatic vision is possible only under sufficiently bright illumination. The fish species discussed here have large eyes (diameters up to 100 mm) with large pupils and huge cones. Thus the quantum flux collected by one fish cone can be much higher than the flux collected by a human cone under corresponding conditions. Furthermore the temperature in the deep ocean is only 5-10 centigrades, and thus the cones of these more or less poikilotherm fish have long integration times further increasing their sensitivity. Thus we think that fish may use color vision at depths of 200-400 meters.
Tom Reuter and Leo Peichl*
University of Helsinki, Finland
*Max Planck Institute for Brain Research, Frankfurt, Germany
References
Fritsches, K.A., L. Litherland, N. Thomas and J. Shand. 2003. Cone visual pigments and retinal mosaics in the striped marlin. Journal of Fish Biology 63:1347-1351.
Griebel, U., and L. Peichl. 2003. Colour vision in aquatic mammals: facts and open questions. Aquatic Mammals 29: 18-30.
Loew, E.R., W.N. McFarland and D. Margulies. 2002. Developmental changes in the visual pigments of the yellowfin tuna, Thunnus albacares. Marine and Freshwater Behavior and Physiology 35: 235-246.
Reuter, T., and L. Peichl. 2008. Structure and function of the retina in aquatic tetrapods; pp. 149-172 in J.G.M. Thewissen and S. Nummela (eds.), Sensory Evolution on the Threshold. Adaptations in secondarily aquatic vertebrates. University of California Press, Berkeley.
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