Spectral sensitivity of phototaxis in the dinoflagellate Kryptoperidinium foliaceum and their reaction to physical encounters.

The dinoflagellate Kryptoperidinium foliaceum possesses one of the largest eyespots among the autotrophic dinoflagellates. Until now they were believed to be negatively phototactic using a non-opsin photopigment. Here we provide evidence that in newly established cultures they are positively phototactic and that the dynamic range of phototaxis is ∼2.5 log units. Additionally, we find that the spectral sensitivity of the phototaxis agrees reasonably well with the absorption curve of a theoretical opsin, with a peak sensitivity around 500 nm. The sensitivity in the short wavelength end of the tested spectrum is unexpectedly low, but this is probably due to selective filtering. Interestingly, the phototaxis could be temporarily overruled by tactile stimuli. After physical contact with the light guide, the cells escaped the area, and we suggest that this may serve as predator avoidance.