Experiments on the resynthesis of symbiosis in Convoluta roscoffensis with different flagellate cultures

Abstract

The symbiotic condition of Convoluta roscoffensis has been resynthesized in vitro by feeding new-born colourless larvae with various clones of Platymonas convolutae Parke & Manton available in culture. Greening has also been brought about by feeding larvae with other species distinguishable from the natural symbiont by pyrenoid characters, but subsequent growth of the greened larvae was less and the length of time required for greening greater. The minimum presentation time effective in initiating greening with alien symbionts in 100% of tested larvae was also greater. Cell multiplication of successful symbionts is mitotic, division stages being demonstrated in sections of worms with different types of symbiont. When cultures of potential symbionts were made available competitively in pairs, greening normally involved only one member of a pair, success being apparently determined by the order of relative efficiency demonstrated in the single-culture infections. A chimaeral condition, with two different symbionts present together, was produced and is demonstrated—but only as a temporary phase in an experiment designed to give an alien symbiont a very long start before admitting the real one. In this experiment effective greening with Prasinocladus marinas did not impede prompt entry of Platymonas convolutae when it was supplied, and this was followed by rapid and complete elimination of the alien symbiont. An interpretation of these various findings is discussed in a preliminary way.

A Physiological Comparison of the Symbiotic AlgaPlatymonas Convolutaeand its Free-Living Relatives

“…Indeed, Keeble & Gamble (1907) describe and illustrate the algal cells lying in pairs on an egg case of C. roscoffensis. This argument would also apply to Prasinocladus species and flagellates of this genus can enter into an artificially induced symbiosis in the absence of P. convolutae (Provasoli et al 1968). As well as this, Prasinocladus species show a similar impermeability to carbohydrates to that of P. convolutae and so the observations of Provasoli et al support the idea that the impermeability of the algal cell might be an important factor in the symbiotic relationship.…”

Tetraselmis indica(Chlorodendrophyceae, Chlorophyta), a new species isolated from salt pans in Goa, India

“…A number of species occur in freshwater habitats (John et al, 2002). Some species have been described as endosymbionts of marine animals, including Tetraselmis convolutae which is a facultative symbiont of the acoel flatworm Symsagittifera (Convoluta) roscoffensis Provasoli et al, 1968;Serodio et al, 2011), and an undescribed Tetraselmis species that has been isolated from the radiolarian Spongodrymus.…”

Early ontogenetic expression of specificity in a cnidarian-algal symbiosis

“…In systems with horizontal transmission, the symbionts are acquired during early ontogeny either by the larvae or by the newly metamorphosed polyps. Many studies have characterized the initial acquisition of zooxanthellae by aposymbiotic larvae and newly settled polyps and the reacquisition of zooxanthellae by aposymbiotic (bleached) adults (Provasoli et al 1968, Kinzie 1974, Fitt 1984, Colley & Trench 1985, Schwarz et al 1999), but none have followed this event in a natural setting over extended periods. Trench (1988Trench ( , 1997 and Douglas (1998) have suggested that many algal types initially enter the host and over time, less efficient and/or less competitive genotypes are replaced or displaced.…”