Meeting Abstract
The amount of light entering an eye is functionally important: too much can damage tissue and not enough can affect the quality of images formed. To modulate the amount of light that enters their eyes, cephalopods and vertebrates have pupils that contract and dilate in response to changing light conditions. Scallops (Family Pectinidae) may gain similar benefits from a pupillary response, but one has yet to be documented for their unique mirror-based eyes. By varying light conditions and monitoring the eyes of live, intact bay (Argopecten irradians) and sea (Placopecten magellanicus) scallops, we were the first to document pupil responses in a bivalve mollusk. After we dark-adapted animals for two hours and then exposed them to bright, white light, we found that the pupils of bay scallops contracted by 63 ± 3 µm (mean ± SE), a decrease in diameter of 17 ± 1% (N = 12). Similarly, we found that the pupils of sea scallops contracted by 34 ± 3 µm, equal to a 13 ± 1% decrease in diameter (N = 16). In both species, a majority of the pupillary response occurred in the first minute of light exposure. Once we returned animals to the dark, their pupils tended to dilate to their original, dark-adapted width within an hour. The amount of light that enters an eye is proportional to the square of pupil diameter, suggesting that the pupil contractions we observed in bay and sea scallops were associated with decreases in sensitivity of 31% and 24%, respectively. In additional experiments, we observed pupil responses under intensities of white light that varied over a range of 103 and under both narrow-spectrum blue (470 nm) and green (525 nm) light. Although the pupil responses of scallops may do relatively little to compensate for changes in light intensity, they may be useful for striking an optimal balance between sensitivity and image quality under different light conditions.
