Living Sands: Symbiosis between Foraminifera and Algae

Abstract

All of today's larger foraminifera ({''}living sands{''}) arehosts to endosymbiotic algae. Members of various soritacean families(Peneroplidae, Archaiasidae, Soritidae, Alveolinidae) in contemporarytropical and semitropical seas are hosts for unicellular red, chlorophyte,dinoflagellate and diatom endosymbionts, respectively. Although thehosts seem to require the algae, because they die in the dark, evenwhen they are fed, or in the light when their algal partners areinhibited by DCMU (3-3,4-dichlorophenyl)-1,1-dimethyl urea), thealgal symbionts do not seem to require their hosts. They grow wellin ordinary laboratory media when they are liberated by experimentalmanipulation. A cladistic analysis of the superfamily Soritacea,splits it into 3 clades (Gudmundsson 1994). Each clade is a hostto a different algal type (rhodophyte, chlorophyte, or dinoflagellate).This symbiont diversity is in contrast to the corals, in the samewarm, well illuminated seas, which are hosts only to many kinds ofdinoflagellates. Since most of today's scleractinian families originatedat various times in the Mesozoic, and since they are all hosts fordinoflagellates, it is reasonable to assume that the later evolvingsoritids acquire(d) their zooxanthellae from environmental poolscontributed by the corals in their habitat. Diatom-bearing hostsare not finical in their relationships with their endosymbionts.Although any host can harbor anyone of a score of