Sterility barriers among species ofGracilaria(Rhodophyta, Gigartinales) from the São Paulo Littoral, Brazil

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Abstract
Male gametophytes and cystocarpic plants of Gracilaria cervicornis, G. mammillaris, G. aff. verrucosa, Gracilaria sp. 1 (textorii-type male) and Gracilaria sp. 2 (chorda-type male) were collected at Ubatuba, São Paulo. The species were kept at 21 ± 3°C, 40 μmol m-2 s-1 and 16: photoperiod. Female plants were obtained from tip fragments of cystocarpic specimens. These were kept long enough to ensure the absence of fertilized carpogonia. Control intraspecific crossings were always positive. None of the combinations of male and female pairs produced carpospores. However, female gametophytes of G. mammillaris formed “cystocarps” in the presence of male gametophytes of C. cervicornis, but these cystocarpiclike structures did not develop carpospores. Similar results were obtained with female gametophytes of Gracilaria sp. 1 in the presence of male gametophytes from G. aff. verrucosa. The results indicate that the integrity of the five species is maintained by sterility barriers. This is supported by the existence of discrete morphological populations occurring sympatrically in the area.