Browsing by Author "Stam, W. T."
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- Characterization of microsatellite loci in the dwarf eelgrass Zostera noltii (Zosteraceae) and cross-reactivity with Z. japonicaPublication . Coyer, J. A.; Reusch, T. B. H.; Stam, W. T.; Serrão, Ester; Pearson, G. A.; Procaccini, G.; Olsen, J. L.Zostera noltii is an important species of eelgrass occurring along European, north African, Mediterranean, Black Sea and Azov Sea coasts. Nine microsatellite loci were developed and no linkage disequilibrium was observed. Cross-amplification was observed for all loci (polymorphic) in Z. japonica ; only four loci amplified (monomorphic) in Z. marina.
- Convergent adaptation to a marginal habitat by homoploid hybrids and polyploid ecads in the seaweed genus FucusPublication . Coyer, J. A.; Hoarau, G.; Pearson, G. A.; Serrão, Ester; Stam, W. T.; Olsen, J. L.Hybridization and polyploidy are two major sources of genetic variability that can lead to adaptation in new habitats. Most species of the brown algal genus Fucus are found along wave-swept rocky shores of the Northern Hemisphere, but some species have adapted to brackish and salt marsh habitats. Using five microsatellite loci and mtDNA RFLP, we characterize two populations of morphologically similar, muscoides-like Fucus inhabiting salt marshes in Iceland and Ireland. The Icelandic genotypes were consistent with Fucus vesiculosus x Fucus spiralis F1 hybrids with asymmetrical hybridization, whereas the Irish ones consisted primarily of polyploid F. vesiculosus.
- Evaluating signatures of glacial refugia for North Atlantic benthic marine taxaPublication . Maggs, C. A.; Castilho, Rita; Foltz, D.; Henzler, Christy; Jolly, Marc Taimour; Kelly, J.; Olsen, J. L.; Perez, K. E.; Stam, W. T.; Väinölä, R.; Viard, F.; Wares, J.A goal of phylogeography is to relate patterns of genetic differentiation to potential historical geographic isolating events. Quaternary glaciations, particularly the one culminating in the Last Glacial Maximum ;21 ka (thousands of years ago), greatly affected the distributions and population sizes of temperate marine species as their ranges retreated southward to escape ice sheets. Traditional genetic models of glacial refugia and routes of recolonization include these predictions: low genetic diversity in formerly glaciated areas, with a small number of alleles/ haplotypes dominating disproportionately large areas, and high diversity including ‘‘private’’ alleles in glacial refugia. In the Northern Hemisphere, low diversity in the north and high diversity in the south are expected. This simple model does not account for the possibility of populations surviving in relatively small northern periglacial refugia. If these periglacial populations experienced extreme bottlenecks, they could have the low genetic diversity expected in recolonized areas with no refugia, but should have more endemic diversity (private alleles) than recently recolonized areas. This review examines evidence of putative glacial refugia for eight benthic marine taxa in the temperate North Atlantic. All data sets were reanalyzed to allow direct comparisons between geographic patterns of genetic diversity and distribution of particular clades and haplotypes including private alleles. We contend that for marine organisms the genetic signatures of northern periglacial and southern refugia can be distinguished from one another. There is evidence for several periglacial refugia in northern latitudes, giving credence to recent climatic reconstructions with less extensive glaciation.
- North Atlantic phylogeography and large-scale population differentiation of the seagrass Zostera marina L.Publication . Olsen, J. L.; Stam, W. T.; Coyer, J. A.; Reusch, T. B. H.; Billingham, M. R.; Boström, C.; Calvert, E.; Christie, H.; Granger, S.; La Lumière, R.; Milchakova, N.; Oudot-Le Secq, M.- P.; Procaccini, G.; Sanjabi, B.; Serrão, Ester; Veldsink, J.; Widdicombe, S.; Wyllie-Echeverria, S.As the most widespread seagrass in temperate waters of the Northern Hemisphere, Zostera marina provides a unique opportunity to investigate the extent to which the historical legacy of the last glacial maximum (LGM18 000–10 000 years BP) is detectable in modern population genetic structure. We used sequences from the nuclear rDNA–internal transcribed spacer (ITS) and chloroplast mat K-intron, and nine microsatellite loci to survey 49 populations (> 2000 individuals) from throughout the species’ range. Minimal sequence variation between Pacific and Atlantic populations combined with biogeographical groupings derived from the microsatellite data, suggest that the trans-Arctic connection is currently open. The east Pacific and west Atlantic are more connected than either is to the east Atlantic. Allelic richness was almost two-fold higher in the Pacific. Populations from putative Atlantic refugia now represent the southern edges of the distribution and are not genetically diverse. Unexpectedly, the highest allelic diversity was observed in the North Sea–Wadden Sea–southwest Baltic region. Except for the Mediterranean and Black Seas, significant isolation-by-distance was found from ~150 to 5000 km. A transition from weak to strong isolation-by-distance occurred at ~150 km among northern European populations suggesting this scale as the natural limit for dispersal within the metapopulation. Links between historical and contemporary processes are discussed in terms of the projected effects of climate change on coastal marine plants. The identification of a high genetic diversity hotspot in Northern Europe provides a basis for restoration decisions.
- Population genetics of dwarf eelgrass Zostera nolti throughout its biogeographic rangePublication . Coyer, J. A.; Diekmann, Onno; Serrao, Ester; Procaccini, G.; Milchakova, N.; Pearson, Gareth; Stam, W. T.; Olsen, J. L.The marine angiosperm Zostera noltii (dwarf eelgrass), an important facilitator species and food source for invertebrates and waterfowl, predominantly inhabits intertidal habitats along eastern Atlantic shores from Mauritania to southern Norway/Kattegat Sea and throughout the Mediterranean, Black and Azov seas. We used 9 microsatellite loci to characterize population structure at a variety of spatial scales among 33 populations from 11 localities throughout the entire biogeographic range. Isolation by distance analysis suggested a panmictic genetic neighborhood of 100 to 150 km. At the global scale, a neighbor-joining tree based on Reynolds distances revealed strongly-supported groups corresponding to northern Europe, Mauritania and the Black/Azov Sea; separate Mediterranean and Atlantic-Iberian groups were poorly supported. Clones (genets with multiple ramets) were present in most populations but were generally small (ca. < 3 m(2)). Exceptions were found in Mauritania (ca. 29 m in length), the Azov Sea (ca. 40 m in length) and the Black Sea (ca. 50 m in length). Although genetic diversity and allelic richness generally decreased from Mauritania to Denmark, the putative post-glacial recolonization route, both were unexpectedly high among populations from the German Wadden Sea.
- Population genetics of dwarf eelgrass Zostera noltii throughout its biogeographic rangePublication . Coyer, J. A.; Diekmann, O. E.; Serrão, Ester; Procaccini, G.; Milchakova, N.; Pearson, G. A.; Stam, W. T.; Olsen, J. L.The marine angiosperm Zostera noltii (dwarf eelgrass), an important facilitator species and food source for invertebrates and waterfowl, predominantly inhabits intertidal habitats along eastern Atlantic shores from Mauritania to southern Norway/Kattegat Sea and throughout the Mediterranean, Black and Azov seas. We used 9 microsatellite loci to characterize population structure at a variety of spatial scales among 33 populations from 11 localities throughout the entire biogeographic range. Isolation by distance analysis suggested a panmictic genetic neighborhood of 100 to 150 km. At the global scale, a neighbor-joining tree based on Reynolds distances revealed strongly-supported groups corresponding to northern Europe, Mauritania and the Black/Azov Sea; separate Mediterranean and Atlantic-Iberian groups were poorly supported. Clones (genets with multiple ramets) were present in most populations but were generally small (ca. <3 m2). Exceptions were found in Mauritania (ca. 29 m in length), the Azov Sea (ca. 40 m in length) and the Black Sea (ca. 50 m in length). Although genetic diversity and allelic richness generally decreased from Mauritania to Denmark, the putative post-glacial recolonization route, both were unexpectedly high among populations from the German Wadden Sea.
- Population genetics of Zostera noltii along the west Iberian coast: Consequences of small population size, habitat discontinuity and near-shore currentsPublication . Diekmann, O. E.; Coyer, J. A.; Ferreira, J.; Olsen, J. L.; Stam, W. T.; Pearson, G. A.; Serrão, EsterThe effects of oceanographic patterns on marine genetic biodiversity along the SW Iberian Peninsula are poorly understood. We addressed the question of whether gene flow in this region depends solely on geographic distance between isolated patches of suitable habitat or if there are superimposed effects correlated with other factors such as current patterns. Zostera noltii, the dwarf eelgrass, is the keystone habitat-structuring seagrass species on intertidal mudflats along the Iberian west coast. We used 9 microsatellite loci to analyze population genetic diversity and differentiation for all existing 8 populations from NW Spain (Ria de Vigo) to SW Spain (Puerto Real, Cadiz). Populations are highly genetically differentiated as shown by high significant FST,Wright’s fixation index, (0.08 to 0.26) values. A neighbor-joining tree based on Reynold’s distances computed from allele frequencies revealed a split between northern and southern populations (bootstrap support of 84%). This pattern of differentiation can be explained by (1) ocean surface current patterns present during Z. noltii’s reproductive season which cause a dispersal barrier between the northern and southern populations of this region, (2) habitat isolation, due to large geographic distances between suitable habitats, preventing frequent gene flow, and (3) small effective population sizes, causing high drift and thus faster differentiation rates.