Genetic variation in Symbiodinium isolates from giant clams based on random-amplified-polymorphic DNA (RAPD) patterns

We have compared the random-amplified-polymorphic DNA (RAPD) patterns of Sy mbiodinium isolates from seven species of giant clams to investigate the la rge genetic variation that we previously reported for this group of dinofla gellate symbionts using allozyme analysis. Comparisons of 163 RAPD characte rs by unweighted pair-group arithmetic-average cluster analysis (UPGMA) cor roborate our previous findings that giant clams associate with a large numb er of genetically distinguishable algal symbionts, and that the isolates fr om a single Tridacna gigas individual form a group of closely related algae . However, the overall topology of the UPGMA tree constructed from RAPD dat a differs From that of the previous allozyme data, indicating that the comb ined data we have collected to date are insufficient to accurately infer ph ylogenetic affiliations between the isolates studied. Comparisons of our da ta set with those published for strains of Gymnodinium catenatum, a toxic d inoflagellate with a sexual life stage, shows that our isolates are even mo re diverse. Algal isolates from giant clams have a level of RAPD variation comparable to organisms that are able to undergo sexual recombination. This study demonstrates the sensitivity of the RAPD technique in detecting gene tic diversity in this group of algae, and highlights the need for more comp arative data for the major clades of Symbiodinium.