North Pacific and North Atlantic digitate Laminaria species (Phaeophyta): hybridization experiments and temperature responses

Hybridization was attempted between the marine brown algae (Phaeophyta) Laminaria setchellii P.C. Silva and L. bongardiana Postels et Ruprecht from the north-eastern Pacific and L. hyperborea (Gunnerus) Foslie, L. digitata (Hudson) Lamouroux and L. ochroleuca De la Pylaie from the North Atlantic. No viable hybrids were produced, indicating a rather distant Pacific-Atlantic relationship in the section Digitatae of the genus Laminaria. By contrast, western and eastern Atlantic isolates of L. digitata hybridized readily, and sporophytes up to the F3 generation were produced. Temperature requirements for growth, survival and gametogenesis were determined. The Arctic L. solidungula J. Agardh was investigated for comparative purposes. The maximum survival temperatures of the sporophytes ranged from 16°C in L. solidungula to 22/23°C in L. ochroleuca. Parthenogenic sporophytes had a 1–2°C lower upper temperature tolerance than normal sporophytes. Laminaria ochroleuca grew optimally at 15°C, but did not survive Doe, L. hyperborea, L. digitata and L. setchellii grew optimally at 10–15°C, L. bongardiana at 10°C and L. solidungula at 5–10°C. Gametogenesis was inhibited at 5°C and 21°C in L. ochroleuca, it was inhibited at 17°C in L. bongardiana and L. setchellii, and at 1°C (fertility very reduced) and 21°C in both L. digitata and L. hyperborea.