Genetic variation in the green alga Caulerpa taxifolia

Allozyme surveys of 12 populations of Caulerpa taxifolia collected from the central Great Barrier Reef (GBR) in north-east Australia, Moreton Bay in east Australia, and the western Mediterranean, including populations with fine and robust morphologies, revealed little overall genetic differentiation. Exceptions to the general rule were detected, nonetheless, among the allozymes of oxaloacetate-decarboxylating and non-oxaloacetate-decarboxylating malate dehydrogenase (ME and MDH, respectively). Variation in the allozymes of ME, in particular, indicated that populations with robust form in eastern Australia may be genetically mon similar to populations with similar morphology in the Mediterranean than to populations with fine morphology in the central GBR. All Mediterranean populations, and the robust form from Australia were monomorphic for allele b, while the fine Australian populations had a number of different alleles, including allele b, but most commonly alleles c, d, g, and i. Comparative surveys of one eastern Mediterranean and two western Atlantic populations of Caulerpa mexicana demonstrated clear genetic differentiation from C. taxifolia, with fixed gene differences at several loci. There was little differentiation among populations of C, mexicana. These results suggest that allozyme markers could assist species identification of Caulerpa species on broad geographical scales, but also raises the question of whether there is high gene exchange today throughout the range of Caulerpa species. (C) 2000 Elsevier Science B.V. All rights reserved.