Eye function of Mysis relicta Lovén (Crustacea) from two photic environments. Spectral sensitivity and light tolerance

Spectral sensitivities, S(λ), and light tolerances of the eyes of two geographically isolated populations of the opossum shrimp Mysis relicta Lovén were studied by recording the electroretinogram. Measurements of the downward irradiance of light in the different water localities revealed a correlation between the spectral sensitivity peak of the mysid eye and the light-transmission properties of the water. Eyes of animals from the “red-transmitting” Lake Pääjärvi (transmission maximum 600–700 nm) had a S(λ) max at ≈ 570 nm. The sensitivity of dark-adapted eyes was markedly suppressed by moderate light exposures. Three days of recovery in darkness restored eye sensitivity. Eyes of animals from Pojoviken bay (part of the Baltic Sea, transmission maximum in 565–585 nm) had a S(λ) max of ≈ 550 nm, and upon bright light exposures the sensitivity of the eyes recovered to the sensitivity of the dark-adapted state in ≈ 24 h. These results have a bearing on the adaptional and evolutionary forces acting on the mysid eye, and on the occurrence of sibling species in the Tvärminne area. The importance of spectral sensitivity and light tolerance on vertical migration as well as the impact of light on photoreceptor membrane disruption are briefly discussed.