DISTRIBUTION OF MEMBERS OF THE CRYPTHECODINIUM-COHNII (DINOPHYCEAE) SPECIES COMPLEX

C. cohnii, a small marine heterotrophic homothallic dinoflagellate, has diversified into a complex of morphologically very similar breeding groups (biological species or sibling species), some of which are widely dispersed. Membership of 2 clones in the same sibling species is shown by their sexual compatibility as determined by genetic complementation in zygotes formed from motility mutants derived from the 2 stocks. Membership in different sibling species is inferred when motility mutants of one strain do not complement those of another. Fifty-six clones representing seaweed enrichments from 54 geographic sites belong to 28 sibling species; 35 clones are members of 7 wide-ranging biological species and 21 are single representatives of 21 other breeding groups within the ranges of the others. Of 174 clonal isolates, 168 conform in size and shape to C. cohnii. Six others which have smaller cells and only 1/5 the standard DNA and chromosome number belong to another species. The C. cohnii complex provides a unique opportunity for the study of evolutionary divergence and geographical dispersion of a dinoflagellate.