Chemical races in the red alga Laurencia nipponica (Rhodomelaceae, Ceramiales)

SUMMARY Genetic variation in the synthesis of halogenated secondary metabolites in the Japanese marine red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) has been investigated in laboratory crossing experiments and chemical analyses, F 1 tetrasporophytes and F 1 gametophytes resulting from crosses within chemical races produced major metabolites characteristic of these races. F 1 tetrasporophytes derived from reciprocal interracial crosses produced: (i) both parental types of secondary metabolites; (ii) either of the parental types; or (iii) a further major compound in addition to both parental types or in addition to either of the parental types. The latter cases suggest that hybrid‐specific products were formed by the combined enzymatic complements of the parents, as F 1 gametophytes derived from these interracial F 1 tetrasporophytes yielded one or other of their parental products in an approximate 1:1 ratio. The population structure was analyzed at localities in Hokkaido, where two of the chemical races occur sympatrically. At Usujiri (Minami‐kayabe), where the prepacifenol race and the laureatin race were sym‐patric, hybrid gametophytes (recombination type) were found in high frequency in addition to hybrid tetra sporophytes, which strongly suggests that a new, pre‐pacifenol/laureatm race is beginning to be produced by natural hybridization and recombination. By contrast, at Oshoro Bay, where the laurencin race and the epi‐lauraliene race grew together, the interracial hybrids were rare: only a few tetrasporophytes (probably F 1 generation) were found, suggesting that racial integrity may be retained by habitat segregation and/or the absence of recombination‐type gametophytes.