INTRA-CLONAL VARIATION IN THE RED SEAWEED GRACILARIA-CHILENSIS

The phenotypic plasticity often found in seaweed populations has been explained only from the perspective of inter-population or inter-indiv idual differences. However, many seaweeds grow and propagate by fragme ntation of genetically identical units, each with the capacity to func tion on its own. If significant differences in performance exist among these supposedly identical units, such differences should be expresse d upon the release and growth of these units. In this study we documen t two such types of variation in the red seaweed Gracilaria chilensis. Populations of sporelings, each grown under similar culture condition s and derived from carpospores shed by the same cystocarp exhibit sign ificant differences in growth. In this species, each cystocarp develop s from a simple gametic fusion, and cystocarp fusions occur too infreq uently to account for the growth differences observed among recruits. In adult thalli, branches (ramets) derived from the same thallus (gene t) and grown under similar conditions exhibit significant variation in growth rates and morphology. These findings have several implications . They suggest that carpospore production is not only an example of zy gote amplification but that it also could increase variability among m itotically replicated units. Intra-clonal variability followed by frag mentation and re-attachment may increase intra-population variation wh ich, in species of Gracilaria, is often larger than inter-population v ariation. In addition, the existence of intra-clonal variability sugge sts that strain selection in commercially important species may requir e a more continuous screening of high-quality strains because of frequ ent genotypic or phenotypic changes in the various cultivars.