We used seven microsatellite loci to characterize genetic structure and clonal architecture at three different spatial scales (from meters to centimetres) of a Cymodocea nodosa population. C. nodosa ...exhibits both sexual reproduction and vegetative propagation by rhizome elongation. Seeds remain buried in the sediment nearby the mother plant in a dormant stage until germination. Seed dispersal potential is therefore expected to be extremely restricted. High clonal diversity (up to 67% of distinct genotypes) and a highly intermingled configuration of genets at different spatial scales were found. No significant differences in genetic structure were found among the three spatial scales, indicating that genetic diversity is evenly distributed along the meadow. Autocorrelation analyses of kinship estimates confirmed the absence of spatial clumping of genets at small spatial scale and the expectations of a very restricted seed dispersal (observed dispersal range 1–21 m) in this species.
Genes of the major histocompatibility complex (MHC) have been studied for several decades because of their pronounced allelic polymorphism. Structural allelic polymorphism is, however, not the only ...source of variability subjected to natural selection. Genetic variation may also exist in gene expression patterns. Here, we show that in a natural population of three‐spined sticklebacks (Gasterosteus aculeatus) the expression of MHC class IIB genes was positively correlated with parasite load, which indicates increased immune activation of the MHC when infections are frequent. To experimentally study MHC expression, we used laboratory‐bred sticklebacks that were exposed to three naturally occurring species of parasite. We found strong differences in MHC class IIB expression patterns among fish families, which were consistent over two generations, thus demonstrating a genetic component. The average number of MHC class IIB sequence variants within families was negatively correlated to the MHC expression level suggesting compensatory up‐regulation in fish with a low (i.e. suboptimal) MHC sequence variability. The observed differences among families and the negative correlation with individual sequence diversity imply that MHC expression is evolutionary relevant for the onset and control of the immune response in natural populations.
Plant mating systems have received considerable attention because the proportion of selfed vs. outcrossed progeny is an important evolutionary factor. In clonally reproducing plants, geitonogamous ...selfing between distant ramets belonging to the same genet is expected to be widespread, yet empirical data are sparse. Nothing is known about between‐ramet selfing in aquatic flowering plants with subaqueous pollen transfer, most of which display pronounced clonal reproduction. From two locations in the western Baltic Sea, I present data on the effects of patch isolation and clonal diversity on the outcrossing rate of eelgrass, Zostera marina L., based on the genotypes of maternal plants and recently fertilized ovules scored at eight microsatellite loci. There were no differences in outcrossing rates between vegetation patches and continuous meadow although patches were nearly always composed of single genets. Quantitative effects of clonal diversity were present in the continuous vegetation where a significant positive correlation between genet diversity and the proportion of outcrossed offspring was detected (Kendall’s τ=0.82, P=0.0017). On a population‐scale as well, the genotypic diversity was positively correlated with outcrossing. The relative fitness of selfed offspring was low (ω ± 95% confidence interval=0.56 ± 0.032 and 0.322 ± 0.15) indicating that geitonogamy incurred substantial fitness costs. Selfing rates in Z. marina may not be in evolutionary equilibrium because of spatial and temporal heterogeneity of clonal size and diversity. The high prevalence of dioecy in seagrasses may have evolved to avoid the fitness costs associated with geitonogamy.
We have developed an X-ray scattering setup which allows to study membrane fusion intermediates or other nonlamellar lipid mesophases by laboratory-scale X-ray sources alone, thus taking advantage of ...unrestricted beamtime compared to synchrotron sources. We report results of a study of pure lipid bilayers and phospholipid/cholesterol binary mixtures. Stalks, putative intermediate structures occurring during the membrane fusion process, can clearly be identified from reconstructed electron density maps. Phase diagrams of the lyotropic phase behavior of DOPC/cholesterol and DPhPC/cholesterol samples are presented. If cholesterol is present in moderate concentrations, it can substantially promote the formation of stalks at higher degree of hydration. In addition, a possibly new phase in DOPC/cholesterol is found at high cholesterol content in the low humidity range.
We use standing surface acoustic waves to induce coherent phonons in model lipid multilayers deposited on a piezoelectric surface. Probing the structure by phase-controlled stroboscopic x-ray pulses ...we find that the internal lipid bilayer electron density profile oscillates in response to the externally driven motion of the lipid film. The structural response to the well-controlled motion is a strong indication that bilayer structure and membrane fluctuations are intrinsically coupled, even though these structural changes are averaged out in equilibrium and time integrating measurements. Here the effects are revealed by a timing scheme with temporal resolution on the picosecond scale in combination with the sub-nm spatial resolution, enabled by high brilliance synchrotron x-ray reflectivity.
We examined the genetic population structure in eelgrass (Zostera marina L.), the dominant seagrass species of the northern hemisphere, over spatial scales from 12 km to 10 000 km using the ...polymorphism of DNA microsatellites. Twelve populations were genotyped for six loci representing a total of 67 alleles. Populations sampled included the North Sea (four), the Baltic Sea (three), the western Atlantic (two), the eastern Atlantic (one), the Mediterranean Sea (one) and the eastern Pacific (one). Microsatellites revealed substantial genetic variation in a plant group with low allozyme diversity. Average expected heterozygosities per population (monoclonal populations excluded) ranged from 0.32 to 0.61 (mean = 0.48) and allele numbers varied between 3.3 and 6.7 (mean = 4.7). Using the expected frequency of multilocus genotypes within populations, we distinguished ramets from genetic individuals (i.e. equivalent to clones). Differences in clonal diversity among populations varied widely and ranged from maximal diversity (i.e. all ramets with different genotype) to near or total monoclonality (two populations). All multiple sampled ramets were excluded from further analysis of genetic differentiation within and between populations. All but one population were in Hardy–Weinberg equilibrium, indicating that Zostera marina is predominantly outcrossing. From a regression of the pairwise population differentiation with distance, we obtained an effective population size Ne of 2440–5000. The overall genetic differentiation among eelgrass populations, assessed as ρ (a standardized estimate of Slatkin’s RST) was 0.384 (95% CI 0.34–0.44, P < 0.001). Genetic differentiation was weak among three North Sea populations situated 12–42 km distant from one another, suggesting that tidal currents result in an efficient exchange of propagules. In the Baltic and in Nova Scotia, a small but statistically significant fraction of the genetic variance was distributed between populations (ρ = 0.029−0.053) at scales of 15–35 km. Pairwise genetic differentiation between European populations were correlated with distance between populations up to a distance of 4500 km (linear differentiation‐by‐distance model, R2 = 0.67). In contrast, both Nova Scotian populations were genetically much closer to North Sea and Baltic populations than expected from their geographical distance (pairwise ρ = 0.03−0.08, P < 0.01). A biogeographical cluster of Canadian with Baltic/North Sea populations was also supported using a neighbour‐joining tree based on Cavalli–Sforza’s chord distance. Relatedness between populations may be very different from predictions based on geographical vicinity.
Habitat configuration is expected to have a major influence on genetic exchange and evolutionary divergence among populations. Aquatic organisms occur in two fundamentally different habitat types, ...the sea and freshwater lakes, making them excellent models to study the contrasting effects of continuity vs. isolation on genetic divergence. We compared the divergence in post‐glacial populations of a cosmopolitan aquatic plant, the pondweed Potamogeton pectinatus that simultaneously occurs in freshwater lakes and coastal marine sites. Relative levels of gene flow were inferred in 12 lake and 14 Baltic Sea populations in northern Germany using nine highly polymorphic microsatellite markers developed for P. pectinatus. We found highly significant isolation‐by‐distance in both habitat types (P < 0.001). Genetic differentiation increased approximately 2.5‐times faster among freshwater populations compared with those from the Baltic Sea. As different levels of genetic drift or population history cannot explain these differences, higher population connectivity in the sea relative to freshwater populations is the most likely source of contrasting evolutionary divergence. These findings are consistent with the notion that freshwater angiosperms are more conducive to allopatric speciation than their life‐history counterparts in the sea, the relative species poor seagrasses. Surprisingly, population pairs from different habitat types revealed almost maximal genetic divergence expected for complete reproductive isolation, regardless of their respective geographical distance. Hence, the barrier to gene flow between lake and sea habitat types cannot be due to dispersal limitation. We may thus have identified a case of rapid incipient speciation in post‐glacial populations of a widespread aquatic plant.
Genes of the major histocompatibility complex (MHC) are indispensable for pathogen defence in vertebrates. With wild‐caught three‐spined sticklebacks (Gasterosteus aculeatus) we conducted the first ...study to relate individual reproductive parameters to both MHC class I and II diversities. An optimal MHC class IIB diversity was found for male nest quality. However, male breeding colouration was most intense at a maximal MHC class I diversity. One MHC class I allele was associated with male redness. Similarly, one MHC class IIB allele was associated with continuous rather than early female reproduction, possibly extending the reproductive period. Both alleles occurred more frequently with increasing individual allele diversity. We suggest that if an allele is currently not part of the optimum, it had not been propagated by choosy females. The parasite against which this allele provides resistance is therefore unlikely to have been predominant the previous year – a step to negative frequency‐dependent selection.
As ecosystem engineers, seagrasses are angiosperms of paramount ecological importance in shallow shoreline habitats around the globe. Furthermore, the ancestors of independent seagrass lineages have ...secondarily returned into the sea in separate, independent evolutionary events. Thus, understanding the molecular adaptation of this clade not only makes significant contributions to the field of ecology, but also to principles of parallel evolution as well. With the use of Dr. Zompo, the first interactive seagrass sequence database presented here, new insights into the molecular adaptation of marine environments can be inferred. The database is based on a total of 14 597 ESTs obtained from two seagrass species, Zostera marina and Posidonia oceanica, which have been processed, assembled and comprehensively annotated. Dr. Zompo provides experimentalists with a broad foundation to build experiments and consider challenges associated with the investigation of this class of non-domesticated monocotyledon systems. Our database, based on the Ruby on Rails framework, is rich in features including the retrieval of experimentally determined heat-responsive transcripts, mining for molecular markers (SSRs and SNPs), and weighted key word searches that allow access to annotation gathered on several levels including Pfam domains, GeneOntology and KEGG pathways. Well established plant genome sites such as The Arabidopsis Information Resource (TAIR) and the Rice Genome Annotation Project are interfaced by Dr. Zompo. With this project, we have initialized a valuable resource for plant biologists in general and the seagrass community in particular. The database is expected to grow together with more data to come in the near future, particularly with the recent initiation of the Zostera genome sequencing project.The Dr. Zompo database is available at http://drzompo.uni-muenster.de/
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