MOLECULAR SYSTEMATICS OF ECTOCARPUS AND KUCKUCKIA (ECTOCARPALES, PHAEOPHYCEAE) INFERRED FROM PHYLOGENETIC ANALYSIS OF NUCLEAR-ENCODED AND PLASTID-ENCODED DNA-SEQUENCES

The phylogeny of Ectocarpus and Kuckuckia strains representing widely separated populations from both hemispheres was inferred from sequence analysis of the internal transcribed spacers of the nuclear ribosomal DNA (ITS 1-5.8S-ITS 2) and the spacer region in the plastid-encoded r ibulose-bis-phosphate-carboxylase (RUBISCO) cistron (partial rbcL-spac er-partial rbcS). Both sequences resulted in. matching phylogenies, wi th the RUBISCO spacer region being most informative at the level of ge nera and species and the internal transcribed spacer sequences at the level of species and populations. Three major clades were formed by st rains previously described by morphology and physiology as Kuckuckia, E. fasciculatus, and E. siliculosus, confirming the validity of these taxa. Ectocarpus and Kuckuckia are regarded as sibling taxa with respe ct to the outgroup species Feldmannia simplex, Hincksia mitchelliae, a nd Pilayella littoralis. The clade formed by sexual E. siliculosus str ains and most asexual Ectocarpus strains was subdivided into several c lades that are consistent with geographical races within E. siliculosu s. The inferred phylogeny of Ectocarpus corresponds generally with res ults from cross-fertilization experiments, morphology, and lipid analy sis. A hypothesis on the origin and dispersal of E. siliculosus sugges ts several natural dispersal events during periods of global cooling a s well as recent and possibly anthropogenic dispersal events.