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We tested effects of light and temperature on survival and development of spores of Chondracanthus squarrulosus to determine their influence on the in situ haploid: diploid population ratio. Initially, reproductive tissues of both phases were induced to release spores under standard laboratory conditions. As in most of the Gigartinales, larger numbers of carpospores were released relative to tetraspores (4:1). Tetraspores, however, had higher germination rates (70% vs. 30%). Gametophytes and tetrasporophytes, germinated from spores, were exposed to light and temperature gradients (45-135 μmol photons m-2 s-1 and 14-30°C). Tetrasporophyte survivorship was negatively affected by high temperatures. In contrast, gametophytes had 100% survival at all temperatures tested and their growth rates were greater than those observed in the tetrasporophytes, particularly at higher temperatures. Therefore, the low germination rate of carpospores and the greater survivorship in the first gametophyte stages at higher temperatures would help explain the dominance of the gametophytes over tetrasporophytes of C. squarrulosus in the Gulf of California. A Leslie matrix based on the number of spores released and adult plant survival demonstrated that it is possible to generate a stable adult plant ratio close to the one that we observed in the field. Inglés

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