INTERSPECIFIC AND INTRASPECIFIC GENETIC-VARIATION IN CAULERPA (CHLOROPHYTA) BASED ON NUCLEAR RDNA ITS SEQUENCES

Caulerpa (Chlorophyta, Ulvophyceae) is a common marine tropical-subtro pical genus of about 70 species, inhabiting the eulittoral zone on roc ks and corals as well as mangroves. The genus is particularly diverse and abundant along southern Australian coasts, where it is thought to have originated. Here, we compare sequences from the nuclear ribosomal cistron among five species of Caulerpa, including nine populations of Caulerpa filiformis from two biogeographic regions: five from Austral ia and four from South Africa. Species relationships were well resolve d by internal transcribed spacer (ITS) sequences and supported by high bootstrap values as follows: (C. germinata (C. simpliciuscula (C. tri faria (C. scalpelliformis (C. filiformis - Australia, C. filiformis - South Africa))))). Nucleotide divergence within C. filiformis was low with four and five nucleotide differences present in ITS1 and ITS2 res pectively. Unexpectedly, the 5.8S rRNA gene showed eight nucleotide di fferences between the Australian and South African populations and may indicate cryptic species. The Australian C. filiformis is probably no t a South African introduction. These sequences provide an independent means for assessment of species relationships and appear, in so far a s limited taxon sampling permits, to follow chloroplast ultrastructura l groupings proposed 20 years ago.