THORNBER, C.S.; Univ. of Rhode Island: Functional properties of algal life cycles

Many species of algae have complex, multiphasic life cycles. These species contain multiple independent, free-living stages that they either obligately or selectively cycle between. The inherent complexities of these life cycles provide unique opportunities for investigating the ecological dynamics and tradeoffs between the different stages. All stages must be able to successfully survive and reproduce for the species to persist. However, some species have heteromorphic life cycles, in which the two phases occupy ecologically distinct niches (e.g. an upright blade vs. a flat crust). Other, closely related species have isomorphic life cycles, in which the two phases are assumed to be occupying the same ecological niche. This latter assumption has been infrequently investigated; I focus upon the relationship between isomorphic haploids and diploids of the red alga Mazzaella flaccida. Although these individuals appear morphologically similar, and occur together in the same habitats year-round, they were found to differ markedly in their reproductive capacity, as well as in their palatability to common intertidal herbivores. These results can explain the apparent demographic overabundance of M. flaccida haploids in many populations and provide insights into the evolution and maintenance of isomorphic life cycles.