Browsing by Author "Reusch, T. B. H."
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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.
- Genetic sub-structure and intermediate optimal outcrossing distance in the marine angiosperm Zostera marinaPublication . Billingham, M. R.; Simões, T.; Reusch, T. B. H.; Serrão, EsterThe spatial distribution of genetic variability depends on the spatial patterns of clonal and sexual reproduction, gene flow, genetic drift and natural selection. Species with restricted dispersal may exhibit genetic structuring within populations with immediate neighbours being close relatives, and may show differentiation among populations. Genetic structuring of a species may have important genetic, evolutionary and ecological consequences including distance-dependent mating success. In this study we used microsatellite markers to show that clones of Zostera marina in a population in the Ria Formosa, Portugal, were aggregated and covered distances of up to 3–4 m. Clones within 4 m of each other exhibited significant and positive coancestry values, reflecting the limited seed dispersal of this species. Hand-pollinations between near (0–10.9 m), intermediate (11–32 m) and far (15 km) individuals resulted in similar levels of seed set, although the near pollinations had higher, although not statistically significant, levels of seed abortion during maturation. Seeds from intermediate-distance pollinations had a significantly higher proportion of seeds germinate and shorter germination time than both the near and far seeds. Similarly, the average number of seedlings produced per pollination, used as an overall estimate of fitness, was significantly greater for the intermediate distance when compared to both near and far pollinations. These results suggest that the genetic structuring observed may result in both inbreeding and outbreeding depression, which gives rise to an intermediate optimal outcrossing distance.
- 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.
- 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.