Nucleotide sequence diversity of the 5S rDNA spacer in the simple blade kelp genera Laminaria, Cymathaere and Kjellmaniella (Laminariales, Phaeophyceae) from northern Japan

SUMMARY Tandem repeats of the 5S ribosomal RNA gene (rDNA) were confirmed for almost all laminarian, cymathaerean and kjellmaniellan species distributed in northern Japan. The nucleotide sequence of the spacer region between tandemly repeated 5S rDNA was investigated for 79 samples from 31 sites. Phylogenetic analysis of the 29 different sequences detected revealed two lineages: (1) Laminaria coriacea group, including Laminaria coriacea Miyabe, Laminaria cichorioides Miyabe, Laminaria sachalinensis (Miyabe) Miyabe, Laminaria yendoana Miyabe, Cymathaere japonica Miyabe et Nagai, Kjellmaniella gyrata (Kjellman) Miyabe and Kjellmaniella crassifolia Miyabe; (2) Laminaria japonica group including Laminaria japonica Areschoug, Laminaria religiosa Miyabe, Laminaria ochotensis Miyabe, Laminaria diabolica Miyabe, Laminaria longipedalis Okamura, Laminaria angustata Kjellman and Laminaria longissima Miyabe. In addition, the latter group was divided into two: subgroup (2a) including L. angustata and L. longissima and subgroup (2b) including L. japonica, L. religiosa, L. ochotensis, L. diabolica and L. longipedalis. Members of the three groups differ from each other in the appearance of ornaments (bullation, gyration and folds) on the surface of the blade. These are absent in group (2a), only present in the early stages of the lifespan of group (2b), and present for the duration of the lifespan in group (1). Genetic distances among samples were extremely small within group (2a). Together with previous crossing studies and data on ocean currents and distribution, these findings suggest that gene flow occurs within group (2b).