Is the frequency of apomeiosis in the Rhodophyta a genetic character?
The small rhodophyte Antithamnionella sarniensis Lyle (Ceramiaceae), a very common species on the Atlantic coast of France, has a normal Polysiphonia-like life cycle (Sundene, 1964), but some tetraspores can give new tetrasporophytes directly (L'Hardy-Halos, 1985). This phenomenon has now been studied in detail (Magne, 1986). Twenty strains were prepared starting from sterile plants collected in various places along three hundred kilometers of shoreline. The strains were kept in stock cultures at a low temperature (14 C) with dim natural light and were propagated only by cutting. Exceptionally, one of these strains originated from an apomeiotic tetraspore, and another one is the original strain of von Stosch (1969), who kindly provided it. All the strains proved to be tetrasporophytic, in accordance with the dominance of tetrasporophytes in the field. The progenies of the different strains have been investigated. For each, material from the stock culture was cultivated in monitored conditions (20°C with cool white light of 20 tE.-m-2.s 1, 12 h.d ') to produce tetraspores. Plantlets issuing from the spore-sets were picked randomly, individually transferred in small glass jars and cultivated until reproductive organs were formed; one hundred plantlets were used of each strain. In numerous strains, the progeny is a mixture of gametophytes and tetrasporophytes; the proportions of tetrasporophytes differ from one strain to another over a range from 0% to 100% and show many intermediate values (Magne, 1986). It can be sup-
Marginal distribution and high heterozygosity of asexual Caloglossa vieillardii (Delesseriaceae, Rhodophyta) along the Australian coasts
In animals and land plants, many asexual species originate through inter‐ or intraspecific crosses, and such heterozygous asexuals frequently are more abundant than their sexual relatives in marginal habitats. Although asexual species have been reported in various macroalgal taxa, detailed information regarding their distribution, heterozygosity, and origin is limited. Because many asexual tetrasporophyte strains of Caloglossa vieillardii have been isolated from South Australia, far from their core tropical habitats, we re‐examined the distribution range of asexual C. vieillardii and genotyped these and other western Pacific strains using an actin gene marker. We confirmed the marginal distribution of the asexuals; however, a small patch of sexual thalli was newly discovered 450 km further west from asexual populations in South Australia. Three heterozygous genotypes and one homozygous genotypes were detected from nine asexual populations; 21 heterozygous strains were obligately asexual, but one homozygous strain suddenly produced sexual gametophytes after several years of culture. We hypothesized that the most abundant heterozygous genotype (defined as type 3/4) in asexual populations occurred by a cross between type 3 and type 4 allele gametophytes, both of which were isolated from the Australian coasts. In the crossing experiments, certain combinations between type 3 females and type 4 males produced tetrasporophytes, which recycled successive tetrasporophytes. In the culture experiments, whereas both sexual and asexual strains successfully produced tetraspores at 12°C, no sexual strains released carpospores below 14°C. However, it is uncertain whether this slight difference of maturation temperature was related to the marginal distribution of asexual C. vieillardii.
The culture of the red algal genus Eucheuma in the Philippines
Abstract The author discusses the recent development and present status of a Eucheuma seaweed farming industry in The Philippines. He describes Eucheuma cultivation methods, assesses farm productivity, and considers the economics of Eucheuma farming by Filipino families. The author concludes with a discussion of current problems and an evaluation of future prospects for the industry.