Meeting Abstract
Studies of the visual system often employ anuran models, yet few data indicate the degree of variance in retinal anatomy and physiology across species. Variance across species is most likely driven by different diel niches, as light intensity varies by 6 orders of magnitude. In the present study, we examined the light sensitivity and optics in nocturnal (Hyla cinerea and Rana pipiens) and diurnal frogs (Oophaga pumilio and Mantella viridis). Using electroretinogram recordings, the minimum light intensity necessary to elicit second order neural responses was determined (scotopic B-wave threshold). In addition, photopic B-wave threshold (i.e., cone response) was determined by introducing constant background illumination. Nocturnal species require approximately 1.5 log units less light to elicit scotopic B-waves as compared to diurnal counterparts. No variance is observed in photopic thresholds, indicating increased visual sensitivity may be limited to rod photoreceptors (PR). In a third experiment, we characterized optical sensitivity. Pupillary diameter was determined using infrared photography, focal length was measured in flash-frozen eye sections, and PR outer segment diameter and length were measured in plastic sections (confirmed with Nomarski microscopy in frozen sections). These measurements were used in the Land sensitivity equation (1981) to estimate optical sensitivity. Results show a strong correlation between optical and physiological sensitivity, providing compelling evidence of variance in the peripheral sense organ, which should be taken into account when building models of central visual processing.
