Monterey Bay Aquarium Research Institute
Marine Botany

Ulva title imageLife History

Phototaxis All Ulva swarmers have eyespots at the base of their flagella. The female gamete has 5500 particles in the outer chloroplast envelope membrane of the eyespot and the male has 4900. As gametes, they are positively phototactic and swim toward the light source. This may be advantageous for increasing dispersal, getting more light for photosynthesis, or for helping mix the gametes. When they fuse, they become negatively phototactic. This makes sense because the little quadriflagellate zygotes need to get to the bottom to begin new holdfasts. Zoospores are negatively phototactic the whole time, going down from the beginning. Interestingly, zoospores have 11,300 particles in their eyespots, similar to the combined gamete number in the zygote when it changes from positively to negatively phototactic. So the lower number of particles in the gametes may be related to their positive photaxis. more life history