A study of sexual and asexual populations ofScytosiphon lomentaria(Scytosiphonaceae, Phaeophyceae) in Hokkaido, northern Japan, using molecular markers

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Abstract
The presence or absence of gamete fusion in the dioecious and isogamous brown alga Scytosiphon lomentaria (Scytosiphonaceae, Phaeophyceae) was investigated for thalli collected from three localities, Oshoro, Asari and Muroran in Hokkaido, northern Japan. Both sexual and asexual thalli were found in each locality. These sexual (35 samples) and asexual thalli (15 samples) were used to establish unialgal cultures. ITS2 sequences were determined in all cultures, the rbcL-spacer-S in 14, and cox3 in 25 cultures. Thirteen haplotypes (A1–4, B, C1–4, D, E1–3) were found in ITS2 sequences (241–252 bp). Ten haplotypes (A1–4, B, C1–4 and D) were found in sexual samples: haplotypes A and B were found in Oshoro, C and D in Asari, and C in Muroran. Haplotypes E1–3 were found in asexual samples. Sequence divergence values (including gap information) were less than 4.03% among sexual samples (A, B, C and D types), 0.38–0.77% among asexual samples (E types) and 4.39–5.70% between sexual and asexual samples. In the mitochondrial cox3 gene region (543 bp), six haplotypes (K1–3, L, M and N) were obtained. Cox3-K types were found in samples of ITS2-A types, cox3-L type in ITS2-B type, cox3-M type in ITS2-C and D types, and cox3-N type in ITS2-E types. For cox3 sequences, nucleotide differences were 0.18–4.42% among sexual samples (K, L and M types), but 8.66–10.31% between sexual and asexual samples (N type). In partial rbcL (174 bp)-spacer (188 bp)-partial rbcS (90 bp) sequences, six haplotypes (R–W) were found although there were 1–4 bp nucleotide differences among these haplotypes. R, U and W types were found in sexual samples, and S, T and V types in asexual samples. Results of the sequence analyses suggest that our presumed asexual thalli are genetically different from sexual thalli and may be derived from populations that lack sexual reproduction.