Research

Sensory adaptations to thermal noise: is photoreceptor dark noise in the rockfish (Sebastes) rod cell optimized for environmental temperature?

The rod photoreceptor system, which is responisible for vision in low-light conditions, is an example of a noise-limited sensory system. The absolute sensitivity of retinal rods is limited by noise generated within the rod cell itself (Aho et al. 1988). This 'dark' noise is the result of thermally induced isomerizations of the visual pigment (Baylor et al. 1983). As you might expect, the rate of dark-noise events is related to the photoreceptor temperature, and some ectothermic animals (mostly amphibians) have shown that visual performance in dim light is temperature dependant (Aho et al. 1993). I hypothesized that the visual system of fishes had the potential to increase the ratio of signal to noise, not by increased photon capture efficiency, but through adaptations to specific, predictable sources of noise.

I've addressed this hypothesis using a comparitive approach to examine elements of the scotopic visual system in congeneric species within the genus Sebastes. Study of congeneric species turns out to be pretty nice because, with a little care, you can compare animals with similar natural history, anatomy and ecology. Of the nearly seventy species of rockfish native to the Northeast Pacific coast, I've identified several target species for study; The blue rockfish (S. mystinus), black rockfish (S. melanops), kelp rockfish (S. atrovirens) and olive rockfish (S. serranoides). All the species are common, midwater predators associated with the kelp forests of the central California coast. Interestingly, of these species, blue and black rockfish have been reported as primarily diurnally active species, and kelp and olive rockfish have been reported to forage during crepuscular and nocturnal periods. I've examined the following questions: 1) Does temperature affect low-light visual sensitivity in these species? 2) Do the species visual thresholds correlate with the reported diel activity periods? 3) Are the visual threshold levels, and temperature induced changes in threshold, of an order which might affect the fishes ecology? 4) How do the fishes' thresholds compare to expected light levels in the environment, and can understanding visual threshold levels help predict the ecological impacts of increasing light pollution levels on submarine communities?
For my answers to questions 1 & 2 above, see Reilly And Thompson, 2007. Answers to questions 3 & 4 are in prep.