An evaluation of methods used to assess intergeneric hybridization in kelp using Pacific Laminariales (Phaeophyceae)

Kelp intergeneric laminarialean hybridizations and hybridization protocol were assessed using seven northeast Pacific kelp species: Alaria marginata Postels and Ruprecht, Costaria costata (C. A. Agardh) Saunders, Eisenia arborea Areschoug, Laminaria saccharina (L) Lamouroux, Lessoniopsis littoralis (Tilden) Reinke, Macrocystis integrifolia Bory, and Nereocystis leutkeana (Mertens) Postels and Ruprecht. Survival and development of sporophyte morphologies derived from selfings, separate males and females, and reciprocal crosses were evaluated over 30 weeks of cultivation. All cultures were initiated from cloned gametophytes. Two closely related species, Laminaria angustata Kjellman and L. japonica Areschoug, demonstrated the efficacy of long-term (up to 30 years) cloned gametophytes in hybridization studies. Sporophyte morphologies appeared in 34%-69% of control and hybridization trials, and 6%-16% of all trials produced sporophytes in control and hybridization conditions that persisted through 30 weeks of cultivation. Sporophytes in control and hybridization conditions could appear normal or abnormal. Usually, the morphology of sporophytes in hybridizations and female controls resembled the female parent, whereas the sporophytes in male controls often had an abbreviated morphology, lacking definitive generic features. Species-specific rDNA internal transcribed spacer molecular primers were used to determine the parentage of five putative hybrids. Only the L. japonica female/L. angustata male hybrid bore both parental genomes. That negative controls could produce persistent and normal-appearing sporophytes negates their value and emphasizes the importance of molecular confirmation in hybridization studies. These findings were applied to critique the only known wild intergeneric hybrid, Pelagophycus/Macrocystis.