POPULATION-GENETICS AND TAXONOMY OF CAULERPA (CHLOROPHYTA) FROM THE GREAT-BARRIER-REEF, AUSTRALIA

Allozyme variation was examined in seven species and four varieties of Caulerpa sampled from the Great Barrier Reef (GBR) region, Australia. Differences between species were greater than those between populatio ns of the same taxon sampled from different geographical locations, an d typically included fixed gene differences (no alleles found in one t axon shared by the other taxon) at two or more loci. Three varieties o f C. racemosa, vars imbricata, laetevirens, and racemosa, and a peltat e morph of C. racemosa were as strongly distinguished genetically as t he six other species examined: C. cupressoides, C. lentillifera, C. pe ltata, C. serrulata, C. sertularioides, and C. taxifolia. Cluster anal ysis did not place all of the C. racemosa varieties together and linke d them with other species, but cladistic analyses showed the allozyme data gave little useful phylogenetic information. Eight of 13 plants i dentified initially as C. serrulata were distinguished at several loci , indicating the presence of an undetermined cryptic taxon. Population genetic analysis of polymorphisms, which occurred in some taxa, demon strated strong spatial differentiation among populations of C. cupress oides, C. racemosa vars laetevirens and racemosa, C. serrulata, and C. taxifolia and significant but variable degrees of clonality and/or in breeding within these populations. Allozymes proved to be a useful too l for defining species boundaries and investigating population structu re in Caulerpa, but not for determining phylogenetic relationships wit hin the genus.