Seed Enzyme Polymorphism and Autogamy of the Seagrass Posidonia oceanica from the Western Mediterranean

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Abstract
An exceptionally productive flowering season was observed in the Mediterranean meadows of Posidonia oceanica (L.) Delile in the autumn of 1994. At that time some hermaphroditic inflorescences were bagged, and set fruits, indicating that this species can be self-fertile. By spring 1995, the fruits of P. oceanica had matured; the seeds from nine Mediterranean meadows [French continental (3 populations), Corsica (5 populations) and Tunisian coasts (1 population)] were harvested, weighed and analysed for enzyme diversity. Genetic variability was estimated based on the enzymatic polymorphism of 9 loci. Three of the loci were found to be monomorphic, two were frequently polymorphic within only one population and the remaining four were polymorphic in most of the populations. This demonstrated there was very little genetic variability, with an average observed heterozygosity of 0.0205 for all loci within all populations. According to the Hardy-Weinberg equilibrium, expected heterozygosity was 0.0226. The observed lack of heterozygotes was not statistically significant. The enzyme polymorphism of seeds did not show a geographic diversity pattern although the bio-mass of seeds increased along a north-south gradient suggesting an increased reproductive fitness towards the southern Mediterranean populations. These results support the hypothesis that P. oceanica meadows are made up of a few clones extending over large areas. The clonal growth and self-fertilisation in these populations suggest a predominance of autogamy resulting in a high degree of inbreeding.

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