Biogeographic and phylogenetic studies in three North Atlantic species of Cladophora (Cladophorales, Chlorophyta) using DNA–DNA hybridization

Abstract

The genomes of Cladophora sericea and C. rupestris have been analyzed by means of DNA reassociation kinetics. The organization and complexity of both genomes are very similar. The DNA reassociated as three distinct classes and the single copy DNA components comprise 25–30% of total cell DNA. The haploid genome sizes calculated from the reassociation data are about 3.4 × 10⁸ basepairs. DNA–DNA hybridizations did not reveal detectable differences between Northwest Atlantic, Icelandic and Northeast Atlantic isolates of C. sericea. This suggests that (sub)recent transatlantic dispersal is responsible for the occurrence of C. sericea on both sides of the North Atlantic Ocean. One C. sericea isolate was genotypically deviant; it supports the recognition of a separate species, C. flexuosa (= C. gracilis). Hybridizations between C. sericea DNA and C. ruchingeri DNA, and between C. sericea and C. rupestris DNA showed that in the genus Cladophora interspecific divergence is higher than in most higher eukaryotes.