Aspects of color vision in bluegill sunfish (Lepomis macrochirus): ecological and evolutionary relevance

Summary Spectral sensitivity curves were measured for bluegills using a heart-rate conditioning technique. A mean spectral sensitivity curve (n=3) determined using a white background exhibited two main peaks, indicating the possible presence of two cone photoreceptors mechanisms. Chromatic adaptation was used to separate the contribution of the cone mechanisms to sensitivity. Peak sensitivities were located at 540 and 640 nm against red and blue-green backgrounds, respectively.Light adaptation curves were measured for each cone mechanism indicating that these cone mechanisms have their greatest contrast sensitivity at higher background intensities. Spatial summation properties were also measured for each cone mechanism revealing a critical diameter (summation area) of 5° for both mechanisms.Microspectrophotometric (MSP) measurements were made on individuals from the same group of bluegills used in the above experiments. The results showed the presence of two cone types: single green-sensitive cones with an average _max of 536 nm (SD±1.8nm,n=11) and twin redsensitive cones with an average _max of 620 nm (SD ±1.9 nm,n=11).The correlation between the visual pigment absorption spectra and action spectra of the two cone mechanisms indicate a sound physiological basis for sensitivity. The functional properties of the two cone mechanisms, will be discussed in relation to the ecological and behavioral aspects of bluegills.Abbreviation TVI threshold vs intensity