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PHYCOLOGICAL SOCIETY OF AMERICA

Life History

Life Cycle       Fruiting Patterns       Swarmers       Phototaxis   

Vegetative Reproduction

Fruiting Pattern

The fruiting pattern of Ulva is controlled by the lunar cycle.  In Monterey Bay, as well as the rest of the Pacific Coast of North America, U. lobata releases its gametes during a series of spring tides, whereas U. pertusa in Japan releases its gametes during neap tides.  In both cases, the release appears to be related to the amount of moonlight, as opposed to the associated tidal movement, and in both cases, the release of spores follow the gametes a few days later.  The periodicity of gamete formation and release helps insure genetic exchange within the population.  This is further helped by the fact that each fond is a different sex and therefore cannot self-fertilize.  Interestingly, there is no periodicity observed in Ulva reproduction on the Atlantic coast of the United States.  Maybe there it depends more on nitrogen levels. 

Reproductive activity in U. mutabilis in particular has been studied and was found to be regulated by factors from the blade cells.  When these regulatory factors are excreted into the cell walls and into the environment, the alga remains in a vegetative state.  When the production of a certain regulatory factor decreases below a threshold, which happens as the thallus matures, gametogenesis begins.  

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