Molecular divergence between North Atlantic and Indo-West Pacific Cladophora albida (Cladophorales: Chlorophyta) isolates as indicated by DNA-DNA hybridization

Genomic relationships between North Atlantic, Australian and Japanese isolates of the benthic seaweed Cladophora albida (Huds.) Kütz. were examined in 1987 by means of DNA-DNA hybridization. The data indicate that C. albida can be divided into a North Atlantic and an Indo-West Pacific group with an intergroup hybridization response of 25 to 30% and 5.5° to 6.0°C for hybridization percentage and ΔT me the melting temperature reduction of hybridized sequences, respectively. This level of genome divergence is considerably higher than that observed in most other eukaryotes. The separation between the two C. albida groups presumably dates back to the closure of the Asian part of the Tethys Ocean, about 12 million years ago. The data also indicate that transatlantic C. albida populations have a greater genetic inter-relatedness than have Japanese and Australian populations. In C. albida there is no clear correlation between molecular evolution and the evolution of morphological traits. C. albida and C. rupestris (L.) Kütz have hardly any DNA sequences in common.