Rod-cone based color vision in seals under photopic conditions

Marine mammals have lost the ability to express S-cone opsin, and possess only one type of M/L-cone in addition to numerous rods. As they are cone monochromats they should be color blind. However, early behavioral experiments with fur seals and sea lions indicated discrimination ability between many shades of grey and blue or green. On the other hand, most recent training experiments with harbor seals under "mesopic" conditions demonstrated rod based color blindness (Scholtyssek et al., 2015). In our experiments we trained two harbor seals (Phoca vitulina) and two South African fur seals (Arctocephalus pusillus) with surface colors under photopic conditions. The seals had to detect a triang…