|
Even though studies have not yet been conducted on the algal uptake selectivity of clams, it would make sense that some mechanism would exist. Other (Most) organisms that host symbiotic microbes tend to select for only those that are beneficial, as uptake of pathogenic would be detrimental. The Hawaiian bobtail squid (E. scolops, I believe?) possesses a "light organ" which houses symbiotic V. fischeri. The squid actually selects for this specific species of bacterium on the cellular level via specialized crypt cells, a series of selective host defenses, and communication factors for detection and localization of the bacterium to the light organ. Symbiotic plants with nodules that house nitrogen fixing bacteria also release communication factors into the surrounding soil, which guides the bacterium through uptake. The bacteria also possess a series of factors that are released in order to communicate with the plant. In both cases, squid and plant, there is a two-way communication avenue that each has evolved to form a symbiotic association. What proceeds after uptake is a restructuring of the host organism by the bacterium in order to create a "house" of sorts that allows the bacterium to proliferate. An interesting study would be to examine larval growth and development in photosynthetic clams after aseptic fertilization and exposure to individual species of algal symbionts and non-symbionts.
|