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- New microsatellite markers for the endemic Mediterranean seagrass Posidonia oceanicaPublication . Alberto, F.; Correia, L.; ARNAUD-HAOND, Sophie; Billot, C.; Duarte, C. M.; Serrão, EsterThe seagrass Posidonia oceanica is endemic to the Mediterranean Sea, where it plays an important role in coastal ecosystem dynamics. Because of this important role and concerns about the observed regression of some meadows, population genetic studies of this species have been promoted. However, the markers used until now were not polymorphic enough to efficiently assess the level and spatial pattern of genetic variability. Hypervariable molecular markers were obtained by screening a genomic library enriched for microsatellite dinucleotide repeats. Among 25 primer pairs defined, eight amplified polymorphic microsatellites with an encouraging level of variability at the two geographical scales sampled.
- 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.
- Vicariance patterns in the Mediterranean Sea: East-west cleavage and low dispersal in the endemic seagrass Posidonia oceanicaPublication . ARNAUD-HAOND, Sophie; Migliaccio, M.; Diaz-Almela, E.; Teixeira, Sara; Van De Vliet, M. S.; Alberto, F.; Procaccini, G.; Duarte, C. M.; Serrão, EsterAim The seagrass, Posidonia oceanica is a clonal angiosperm endemic to the Mediterranean Sea. Previous studies have suggested that clonal growth is far greater than sexual recruitment and thus leads to low clonal diversity within meadows. However, recently developed microsatellite markers indicate that there are many different genotypes, and therefore many distinct clones present. The low resolution of markers used in the past limited our ability to estimate clonality and assess the individual level. New high-resolution dinucleotide microsatellites now allow genetically distinct individuals to be identified, enabling more reliable estimation of population genetic parameters across the Mediterranean Basin. We investigated the biogeography and dispersal of P. oceanica at various spatial scales in order to assess the influence of different evolutionary factors shaping the distribution of genetic diversity in this species. Location The Mediterranean. Methods We used seven hypervariable microsatellite markers, in addition to the five previously existing markers, to describe the spatial distribution of genetic variability in 34 meadows spread throughout the Mediterranean, on the basis of an average of 35.6 (± 6.3) ramets sampled. Results At the scale of the Mediterranean Sea as a whole, a strong east–west cleavage was detected (amova). These results are in line with those obtained using previous markers. The new results showed the presence of a putative secondary contact zone at the Siculo-Tunisian Strait, which exhibited high allelic richness and shared alleles absent from the eastern and western basins. F statistics (pairwise θ ranges between 0.09 and 0.71) revealed high genetic structure between meadows, both at a small scale (about 2 to 200 km) and at a medium scale within the eastern and western basins, independent of geographical distance. At the intrameadow scale, significant spatial autocorrelation in six out of 15 locations revealed that dispersal can be restricted to the scale of a few metres. Main conclusions A stochastic pattern of effective migration due to low population size, turnover and seed survival is the most likely explanation for this pattern of highly restricted gene flow, despite the importance of an a priori seed dispersal potential. The east–west cleavage probably represents the outline of vicariance caused by the last Pleistocene ice age and maintained to this day by low gene flow. These results emphasize the diversity of evolutionary processes shaping the genetic structure at different spatial scales.
- 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.
- Characterization of 15 polymorphic microsatellite loci in Rimicaris exoculata, and cross-amplification in other hydrothermal-vent shrimpPublication . Teixeira, Sara; Serrão, Ester; ARNAUD-HAOND, SophieAbstract Rimicaris exoculata is an alvinocarid shrimp endemic to the hydrothermal vents of the Mid-Atlantic Ridge. In order to study genetic variability and connectivity in this species, we developed fifteen polymorphic microsatellite markers. The markers were tested on one population and, except for one, all showed no departure from Hardy–Weinberg equilibrium, with an average overall observed heterozygosity of 0.63. Two primer pairs revealed possible linkage disequilibrium, and 14 crossamplified at least one of the three co-occurring shrimp species tested (Alvinocaris muricola, Alvinocaris markensis and Mirocaris fortunata). These markers therefore open perspectives for population genetic studies of hydrothermal vent shrimp species in order to unravel connectivity and evolution of populations, and to add information on possible future impact studies.
- Within-population spatial genetic structure, neighbourhood size and clonal subrange in the seagrass Cymodocea nodosaPublication . Alberto, F.; Gouveia, Licínia; ARNAUD-HAOND, Sophie; Pérez-Lloréns, J. L.; Duarte, C. M.; Serrão, EsterThe extent of clonality within populations strongly influences their spatial genetic structure (SGS), yet this is hardly ever thoroughly analysed. We employed spatial autocorrelation analysis to study effects of sexual and clonal reproduction on dispersal of the dioecious seagrass Cymodocea nodosa. Analyses were performed both at genet level (i.e. excluding clonal repeats) and at ramet level. Clonal structure was characterized by the clonal subrange, a spatial measure of the linear limits where clonality still affects SGS. We show that the clonal subrange is equivalent to the distance where the probability of clonal identity approaches zero. This combined approach was applied to two meadows with different levels of disturbance, Cadiz (stable) and Alfacs (disturbed). Genotypic richness, the proportion of the sample representing distinct genotypes, was moderate (0.38 Cadiz, 0.46 Alfacs) mostly due to dominance of a few clones. Expected heterozygosities were comparable to those found in other clonal plants. SGS analyses at the genet level revealed extremely restricted gene dispersal in Cadiz (Sp = 0.052, a statistic reflecting the decrease of pairwise kinship with distance), the strongest SGS found for seagrass species, comparable only to values for selfing herbaceous land plants. At Cadiz the clonal subrange extended across shorter distances (20–25 m) than in Alfacs (30–35 m). Comparisons of sexual and vegetative components of gene dispersal suggest that, as a dispersal vector within meadows, clonal spread is at least as important as sexual reproduction. The restricted dispersal and SGS pattern in both meadows indicates that the species follows a repeated seedling recruitment strategy.
- Polymorphic microsatellite DNA markers in the mangrove tree Avicennia albaPublication . Teixeira, Sara; ARNAUD-HAOND, Sophie; Duarte, C. M.; Serrão, EsterLike most species of mangrove trees of the genus Avicennia , A. alba is widely distributed among tropical and subtropical coasts around the world. Mangroves play an essential role in ecosystem dynamics but are reported to be regressing as human pressure increases on coastal zones. Hypervariable genetic markers are useful for population genetics studies, to estimate the level of impact and the populations potential for recovery. Microsatellite markers for A. alba were obtained by screening a partial genomic library enriched for micro-satellite dinucleotide repeats. Among 20 primer pairs defined, six amplified polymorphic microsatellites with a satisfying level of variability.