How long do the plastids retained by Elphidium excavatum (Terquem) last in their host?

Intact plastids are retained by Elphidium excavatum (Foraminifera). There is preferential retention of diatom plastids. Freshly collected specimens of E. excavatum were fed diets of three different axenic cultures of algae for a week, and then starved for 8 weeks to assess the longevity of plastids retained from their diets. The number of plastids retained per individual was assessed weekly with the aid of a confocal laser scanning microscope. Starved individuals served as controls. Since controls already had plastids they retained while they were feeding in the field before they were harvested, we subtracted control values from experimental values to estimate the experimental results. Results indicate that plastids remain in the cytoplasm of Elphidium for at least 8 weeks. When the foraminifera were incubated with 12/12h light/dark cycle, the half-life of diatom plastids was shorter. Although we observed plastids in foraminifera fed chlorophytes or dinoflagellates, the numbers retained were the same or less than starved controls, suggesting that no new plastids had been added to the "symbiont" population during the week of experimental feeding. The half-lives of all retained chloroplasts were longer for hosts that were incubated in the dark (diatom plastids 9.5 weeks; dinoflagellate plastids 4.7 weeks; chlorophyte plastids 8.2 weeks; and plastids [most probably from diatoms] in controls 10.7 weeks). The results are in general accordance with what is known about the kleptochloroplast phenomenon in the ascoglossan mollusk, Elysia chlorotica.