RIBOSOMAL-RNA SEQUENCING OF MEMBERS OF THE CRYPTHECODINIUM-COHNII (DINOPHYCEAE) SPECIES COMPLEX - COMPARISON WITH SOLUBLE ENZYME STUDIES

Sixty-five members of the Crypthecodinium cohnii species complex were analyzed for sequence differences within the D2 region of the 23S ribo somal RNA molecule. On the basis of 46 sequence differences the strain s fell into 19 distinct ribosets (strains of identical sequence), some with many members. Members of four of the seven major sibling species (widespread breeding groups) were each found within single ribosets. Members of three other major sibling species were each, however, divid ed into two ribosets by a single sequence difference correlated with g eographic separation and with previously reported electrophoretic poly morphisms of soluble enzymes within the sibling species. In addition t o members of major sibling species, some ribosets include many minor s ibling species (each represented by only one strain). Of 38 minor sibl ing species, 22 shared sequence with a major sibling species. Of these 22, 14 were identical in soluble enzymes to their related major sibli ng species or differed by only one of three enzymes. Other minor sibli ng species appear to have diverged extensively from any others in both rRNA sequence and electrophoretic profile. As a group, major sibling species differ markedly in the number of minor sibling species associa ted with them, suggesting differences in frequency of sexually isolati ng events in their past histories. These findings are discussed in the context of the previously proposed model of sympatric speciation.