CROSSING EXPERIMENTS, LIPID-COMPOSITION, AND THE SPECIES CONCEPT IN ECTOCARPUS-SILICULOSUS AND E-FASCICULATUS (PHAEOPHYCEAE, ECTOCARPALES)

Sporophytes of Ectocarpus siliculosus (Dillwyn) Lyngbye and E. fascicu latus Harvey were collected in the vicinity of Roscoff, Brittany, Fran ce. Gametophytes derived from meiospores were used for intra- and inte rspecific crosses. Intraspecific gamete combinations gave viable zygot es, which developed into fertile sporophytes. Interspecific crosses we re unsuccessful. Gamete fusions did not occur between female gametes o ff. fasciculatus and male gametes of E. siliculosus. Hybrid zygotes we re formed in the reciprocal combination but died soon after germinatio n. We conclude that the two species of Ectocarpus at Roscoff represent distinct taxonomic entities, which are separated by pre- and postzygo tic compatibility barriers. These biological findings are confirmed by the differential occurrence of the chemotaxonomic marker betaine-lipi d acetylglycerylhydroxymethyltrimethyl-beta-alanine, which is present in our cultures of E. fasciculatus but absent in E. siliculosus.