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Ruggiero, Maria Valeria
(2004).
DOI: https://doi.org/10.21954/ou.ro.0000fa0e
Abstract
In the present thesis, the factors influencing population’s genetic structure in the clonal marine angiosperm Cymodocea nodosa have been investigated. C. nodosa is a dioecious seagrass, exhibiting both vegetative propagation and sexual reproduction. Seed dispersal is expected to be extremely restricted. I selected seven microsatellite loci through genomic library screening to investigate the relative effects of sexual and clonal reproduction on the genetic diversity and structure in a Cymodocea nodosa population from the Gulf of Naples (Italy). High clonal diversity and genet density were found. Autocorrelation analyses confirmed the expectations of very restricted seed dispersal (observed dispersal range 1-21m) in this species. The effect of mating system on genetic structure were investigated comparing the clonal architectures of the dioecious Cymodocea nodosa and monoecious Zostera noltii. An intermingled configuration of genets has been found in the dioecious Cymodocea nodosa while a clumped distribution of clones in the hermaphroditic Zostera noltii has been observed. I hypothesise that the possibility of reduction in the seed-set would drive genet distribution. On a phylogeographic spatial scale, the existence of population differentiation and of genetic disjunction within the Mediterranean Sea was investigated in Cymodocea nodosa. Populations displayed a wide variability in clonal diversity. A Bayesian analysis revealed that “supra-population” panmictic units are present in the Mediterranean basin. Genetic substructure from a phylogeographic tree coincided with major geographical boundaries within the Mediterranean basin. In general, in Cymodocea nodosa, seed dispersal is poor at the within-population level, but long-range dispersal events can occur, allowing high levels of gene flow at a phylogeographic scale. The observed “guerrilla” clonal architecture allows to reduce the effect of genetic identity on the genetic structure of the population, but it is also advantageous by allowing pollen availability and therefore a sufficient seed-set in this dioecious species.