Percorrer por autor "Alberto, F."
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- Assessing genetic diversity in clonal organisms: low diversity or low resolution? Combining power and cost efficiency in selecting markersPublication . ARNAUD-HAOND, Sophie; Alberto, F.; Teixeira, Sara; Procaccini, G.; Serrão, Ester; Duarte, C. M.The increasing use of molecular tools to study populations of clonal organisms leads us to question whether the low polymorphism found in many studies reflects limited genetic diversity in populations or the limitations of the markers used. Here we used microsatellite datasets for two sea grass species to provide a combinatory statistic, combined with a likelihood approach to estimate the probability of identical multilocus genotypes (MLGs) to be shared by distinct individuals, in order to ascertain the efficiency of the markers used and to optimize cost-efficiently the choice of markers to use for deriving unbiased estimates of genetic diversity. These results strongly indicate that conclusions from studies on clonal organisms derived using markers showing low polymorphism, including microsatellites, should be reassessed using appropriate polymorphic markers.
- 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.
- Extending the life history of a clonal aquatic plant: dispersal potential of sexual and asexual propagules of Zostera noltiiPublication . Berković, Buga; Cabaço, Susana; Barrio, Juan M.; Santos, Rui; Serrão, Ester; Alberto, F.The dispersal potential of sexual and asexual propagules of Zostera noltii was experimentally quantified in still water and under different currents in microcosm and mesocosm facilities. We estimated sinking rates of seeds and changes over time in shoot buoyancy, shoot viability, fragment breakage, shoot growth rate and spathe release rate of floating fragments. The fast sinking rates of detached Z. noltii seeds suggest a small spatial scale of dispersal insufficient to connect fragmented populations, whereas the traits of floating fragments, particularly shoot buoyancy and shoot survival (>55 d), suggest a potential for long distance dispersal (>2300 km) that could connect distant patches and allow colonization of new areas. We showed that the Z. noltii vegetative and reproductive fragments have the potential to extend the dispersal achieved by detached seeds alone.
- Fast sporophyte replacement after removal suggests banks of latent microscopic stages of Laminaria Ochroleuca (phaeophyceae) in tide pools in northern PortugalPublication . Barradas, Ana; Alberto, F.; Engelen, Aschwin; Serrão, EsterThis study investigated the effects of a physical disturbance consisting of the removal of adult kelps (Laminaria ochroleuca Bachelot de la Pylaie)and their corresponding understorey turf assemblage in tide pools in northern Portugal.
- Findkelp, a GIS-based community participation project to assess portuguese kelp conservation statusPublication . Assis, J.; Tavares, D.; Tavares, J.; Cunha, A. H.; Alberto, F.; Serrão, EsterIn almost any Atlantic coastal area of Europe where there is a suitable substratum and adequate water quality, one or more species of kelp may be found. Their high productivity and complex biological structure make kelps especially important members of their communities, particularly when present in dense stands known as “kelp forests”. Currently, these species are subject to important novel constraints of physical and anthropogenic origins that can strongly modify their sustainability, their distribution and the biodiversity of associated species. Along the Portuguese coastline there is a perception by the local and scientific communities that some kelp species abundance is declining, particularly at the southern coast. Nevertheless, no large-scale spatial study of kelp abundance and diversity has been done. With the acronym Findkelp, this study aimed to assess from May to August 2008, the Portuguese kelp conservation status through community participation, field-based observations and large-scale Geographic Information System (GIS) technology. A communication strategy towards scuba divers and other coastal zone users was made to build and educate a team of informed volunteers that worked as independent observers, reporting georeferenced data in an electronic data-base available on the project’s website. At randomly underwater chosen locations (n=56) from the volunteers reported sites (n=388), structural descriptors of kelp populations were groundtruthed, by means of non-destructive sampling techniques (3x50m belt-transects). By crossing the volunteer’s reported data with the groundtruthed data, using error matrices and Kappa statistics with concordance agreement scales, a Portuguese coast line GIS map with perfect agreement (K=0.827) was made including the current distribution, diversity and conservation status of 6 kelp species.
- Genetic differentiation and secondary contact zone in the seagrass Cymodocea nodosa across the Mediterranean-Atlantic transition regionPublication . Alberto, F.; Massa, S. I.; Manent, P.; Diaz-Almela, E.; ARNAUD-HAOND, Sophie; Duarte, C. M.; Serrão, EsterAim A central question in evolutionary ecology is the nature of environmental barriers that can limit gene flow and induce population genetic divergence, a first step towards speciation. Here we study the geographical barrier constituted by the transition zone between the Atlantic Ocean and the Mediterranean Sea, using as our model Cymodocea nodosa, a seagrass distributed throughout the Mediterranean and in the Atlantic, from central Portugal to Mauritania. We also test predictions about the genetic footprints of Pleistocene glaciations. Location The Atlantic–Mediterranean transition region and adjacent areas in the Atlantic (Mauritania to south-west Portugal) and the Mediterranean. Methods We used eight microsatellite markers to compare 20 seagrass meadows in the Atlantic and 27 meadows in the Mediterranean, focusing on the transition between these basins. Results Populations from these two regions form coherent groups containing several unique, high-frequency alleles for the Atlantic and for the Mediterranean, with some admixture west of the Almeria–Oran Front (Portugal, south-west Spain and Morocco). These are populations where only one or a few genotypes were found, for all but Cadiz, but remarkably still show the footprint of a contact zone. This extremely low genotypic richness at the Atlantic northern edge contrasts with the high values (low clonality) at the Atlantic southern edge and in most of the Mediterranean. The most divergent populations are those at the higher temperature range limits: the southernmost Atlantic populations and the easternmost Mediterranean, both potential footprints of vicariance. Main conclusions A biogeographical transition region occurs close to the Almeria–Oran front. A secondary contact zone in Atlantic Iberia and Morocco results from two distinct dispersal sources: the Mediterranean and southernmost Atlantic populations, possibly during warmer interglacial or post-glacial periods. The presence of high-frequency diagnostic alleles in present-day disjunct populations from the southernmost Atlantic region indicates that their separation from all remaining populations is ancient, and suggests an old, stable rear edge.
- Genetic diversity of a clonal angiosperm near its range limit: The case of Cymodocea nodosa at the Canary IslandsPublication . Alberto, F.; ARNAUD-HAOND, Sophie; Duarte, C. M.; Serrão, EsterThe seagrass Cymodocea nodosa forms a unique community in the Canary Islands, where it is classified as an endangered species. Biogeographic theory predicts that clonal species on islands near their distributional limits might show lower proportions of sexual (versus clonal) reproduction, lower genetic diversity, and higher differentiation. We addressed these hypotheses by comparing the genetic structure of C. nodosa from 10 meadows in the 4 main Canary Islands with2Iberian sites (Atlantic and Mediterranean) using microsatellites. A resampling method was proposed to standardize, among samples, genetic variability statistics estimating genotypic richness (R) and allelic richness (Â). A high degree of genotypic richness at the Canary Islands (R = 0.30 – 0.94, mean = 0.67) relative to Iberian sites revealed that C. nodosa performs effective sexual reproduction here. In contrast, lower  suggested a founder effect during the colonization of the archipelago, and similar allelic composition across all islands indicated colonization from a single source. A hotspot of genetic diversity was observed in El Medano (Tenerife), probably associated with lower drift in this meadow, the largest of the archipelago. Predominant north-south surface currents and a greater distance to the mainland could explain lower allelic richness of 2 northwestern sites on different islands and greater similarity between them. All meadows were differentiated from each other and there was no correlation between genetic and geographic distances. This non-equilibrium migration-mutation system was therefore mostly influenced by diversity resulting from genetic drift, and less by the homogenizing effects of gene flow.
- High and distinct range-edge genetic diversity despite local bottlenecksPublication . Assis, J.; Castilho Coelho, N.; Alberto, F.; Valero, Myriam; Raimondi, P. T.; Reed, D. C.; Serrão, EsterThe genetic consequences of living on the edge of distributional ranges have been the subject of a largely unresolved debate. Populations occurring along persistent low latitude ranges (rear-edge) are expected to retain high and unique genetic diversity. In contrast, currently less favourable environmental conditions limiting population size at such range-edges may have caused genetic erosion that prevails over past historical effects, with potential consequences on reducing future adaptive capacity. The present study provides an empirical test of whether population declines towards a peripheral range might be reflected on decreasing diversity and increasing population isolation and differentiation. We compare population genetic differentiation and diversity with trends in abundance along a latitudinal gradient towards the peripheral distribution range of Saccorhiza polyschides, a large brown seaweed that is the main structural species of kelp forests in SW Europe. Signatures of recent bottleneck events were also evaluated to determine whether the recently recorded distributional shifts had a negative influence on effective population size. Our findings show decreasing population density and increasing spatial fragmentation and local extinctions towards the southern edge. Genetic data revealed two well supported groups with a central contact zone. As predicted, higher differentiation and signs of bottlenecks were found at the southern edge region. However, a decrease in genetic diversity associated with this pattern was not verified. Surprisingly, genetic diversity increased towards the edge despite bottlenecks and much lower densities, suggesting that extinctions and recolonizations have not strongly reduced diversity or that diversity might have been even higher there in the past, a process of shifting genetic baselines.
- Is asexual reproduction more important at geographical limits? A genetic study of the seagrass Zostera marina in the Ria Formosa, PortugalPublication . Billingham, M. R.; Reusch, T. B. H.; Alberto, F.; Serrão, EsterIn populations of species that are able to reproduce both sexually and asexually, there may be local differences with regard to the relative importance of the 2 modes of reproduction. Studies of plant species with such a life history have shown that the contribution of sexual reproduction to population maintenance may be lower at the geographical margins, with genotypic diversity often used as an indicator of the relative importance of vegetative and sexual reproduction. This hypothesis was examined in a collection of samples of eelgrass Zostera marina (a marine flowering plant) from its eastern Atlantic southern limit (Ria Formosa, Portugal). Samples from 12 sites were genotyped using 9 microsatellite loci to compare within-site clonal and genetic diversity, and among-site distribution of genetic diversity, with previously published values from central sites. Sites within the Ria Formosa had lower clonal diversities (mean = 0.29, range = 0.07 to 0.68) than the central sites (mean = 0.86, range = 0.33 to 1.00), lower levels of expected heterozygosity (He = 0.423 vs 0.486) and exhibited heterozygote excesses rather than deficits. Similarly, genetic differentiation was found to be much greater in the Ria Formosa, with the FST of 0.233 being over 10-fold greater than that reported for populations in the Baltic Sea. Results from this study were consistent with previous findings of reduced sexual reproduction, genotypic diversity and among-population gene flow at species limits.