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- Assessing patterns of geographic dispersal of Gelidium sesquipedale (Rhodophyta) through RAPD differentiation of populationsPublication . Alberto, F.; Santos, Rui; Leitão, J. M.Randomly amplified polymorphic DNAs (RAPDs) of bulked genomic DNA samples were used to analyse the genetic differentiation of Gelidium sesquipedale populations. They reflect the pat terns of gene flow, which in turn depend on the dispersal mechanisms of the species and on near-shore ocean currents. Fourteen populations were sampled from northern France to Morocco, covering the geographical distribution of the species. A single bulk DNA sample (from 15 individuals) was used in each population, under the assumption that the resulting patterns represent the populations' most common genetic features. To test this, we investigated the genetic variability among 5 bulk samples within a single population. Genetic distances among bulks were very low (average = 0.065) and were signifi- cantly lower than those observed between geographically separated populations (average = 0.241). Neighbour-joining analysis of the distance matrix of populations separated a well-supported group including populations of northern Spain and of northern France, and a less-supported group containing populations of northern Portugal. Multidimensional scaling of the genetic distance matrix revealed 2 isolated populations, Sao Rafael in southern Portugal and Algeciras in southern Spain. These patterns of genetic differentiation are discussed under the available data on the near-shore ocean currents. Results suggest that the genetic differentiation of G. sesquipedale populations may be used as a biological tracer of prevailing flows and barriers of the near-shore currents. A positive correlation between geographical and genetic distances of G. sesquipedale populations along the species geographical dis tribution was found, suggesting that a continuous transport of detached fronds and their reattachment to new substrate must be an effective dispersal mechanism of the species, sustaining the gene flow among populations.
- DNA extraction and RAPD markers to assess the genetic similarity among Gelidium sesquipedale (Rhodophyta) populationsPublication . Alberto, F.; Santos, Rui; Leitão, J. M.A simple method developed for genomic DNA isolation from fungus was tested on the red alga, Gelidium sesquipedale (Clem.) Born et Thur., which is commercially exploited for its high sulfated polysaccharide (agar) content. This method is faster, cheaper, and less toxic than conventional phenol/chloroform methods. Random amplified polymorphic DNA (RAPD) amplifications were performed successfully without the necessity of purifying the DNA. RAPD markers were used to investigate the genetic similarity among three natural populations of G. sesquipedale from southern Portugal. Bulked-genomic DNA samples of 15 different individuals were made in each population. These can be conceived of as a sample of the population DNA. Of the 62 primers screened, 41 produced bands and 22 revealed polymorphisms. Genetic similarities among populations were high. Populations that are further away from each other have the lowest similarity coefficients, whereas the intermediate Ingrina population, located on the south coast, showed higher genetic similarity with the Odeceixe population located on the southwest coast, than with the Sao Rafael southern population. This suggests a higher genetic flow between Odeceixe and Ingrina or the result may be a founder effect in the sense that the species has propagated from the east coast to the south coast of Portugal. We conclude that the use of this isolation method with RAPD analysis is appropriate to characterize the genetic variability of this commercial species along its geographical distribution. Large sample sizes can be screened at a relatively low cost. Finding genetic markers for commercial populations of C. sesquipedale may be of industrial interest.