We investigated the distribution of genetic variation within and between seven subpopulations in a riparian population of Silene tatarica in northern Finland by using amplified fragment length polymorphism (AFLP) markers. A Bayesian approach-based clustering program indicated that the marker data contained not only one panmictic population, but consisted of seven clusters, and that each original sample site seems to consist of a distinct subpopulation. A coalescent-based simulation approach shows recurrent gene flow between subpopulations. Relative high FST values indicated a clear subpopulation differentiation. However, amova analysis and UPGMA-dendrogram did not suggest any hierarchical regional structuring among the subpopulations. There was no correlation between geographical and genetic distances among the subpopulations, nor any correlation between the subpopulation census size and amount of genetic variation. Estimates of gene flow suggested a low level of gene flow between the subpopulations, and the assignment tests proposed a few long-distance bidirectional dispersal events between the subpopulations. No apparent difference was found in within-subpopulation genetic diversity among upper, middle and lower regions along the river. Relative high amounts of linkage disequilibrium at subpopulation level indicated recent population bottlenecks or admixture, and at metapopulation levels a high subpopulation turnover rate. The overall pattern of genetic variation within and between subpopulations also suggested a 'classical' metapopulation structure of the species suggested by the ecological surveys.

Genetic substructuring in plant populations may evolve as a consequence of sampling events that occur when the population is founded or regenerated, or if gene dispersal by pollen and seeds is restricted within a population. Silene tatarica is an endangered, perennial plant species growing along periodically disturbed riverbanks in northern Finland. We investigated the mechanism behind the microspatial genetic structure of S. tatarica in four subpopulations using amplified fragment length polymorphism markers. Spatial autocorrelation revealed clear spatial genetic structure in each subpopulation, even though the pattern diminished in older subpopulations. Parentage analysis in an isolated island subpopulation indicated a very low level of selfing and avoidance of breeding between close relatives. The mean estimated pollen dispersal distance (24.10 m; SD 10.5) was significantly longer and the mean seed dispersal distance (9.07 m; SD 9.23) was considerably shorter than the mean distance between the individuals (19.20 m; SD 13.80). The estimated indirect and direct estimates of neighbourhood sizes in this subpopulation were very similar, 32.1 and 37.6, respectively. Our results suggested that the local spatial genetic structure in S. tatarica was attributed merely to the isolation-by-distance process rather than founder effect, and despite free pollen movement across population, restricted seed dispersal maintains local genetic structure in this species. Heredity advance online publication, 2 March 2005; doi:10.1038/sj.hdy.680064

Vegetative dormancy, that is the temporary absence of aboveground growth for ≥ 1 year, is paradoxical, because plants cannot photosynthesise or flower during dormant periods. We test ecological and evolutionary hypotheses for its widespread persistence. We show that dormancy has evolved numerous times. Most species displaying dormancy exhibit life-history costs of sprouting, and of dormancy. Short-lived and mycoheterotrophic species have higher proportions of dormant plants than long-lived species and species with other nutritional modes. Foliage loss is associated with higher future dormancy levels, suggesting that carbon limitation promotes dormancy. Maximum dormancy duration is shorter under higher precipitation and at higher latitudes, the latter suggesting an important role for competition or herbivory. Study length affects estimates of some demographic parameters. Our results identify life historical and environmental drivers of dormancy. We also highlight the evolutionary importance of the little understood costs of sprouting and growth, latitudinal stress gradients and mixed nutritional modes.

Summary1 Although the concept of metapopulation is central to modern conservation biology, plant population biologists have divergent views concerning the importance of metapopulation dynamics. 2 We studied the patch structure and colonization-extinction dynamics of Silene tatarica by mapping its distribution along a 43-km stretch of riverside subjected to annual flood disturbances. Plants were grouped into patches that were surveyed annually. The effect of spatial scale on dynamics was evaluated by varying the interplant separation used to determine grouping from 5 to 200 m. Using the 5-m criterion, the number of patches varied from 703 to 854 over the 5 years of the study. 3 New patches were colonized by a few individuals and located on average 50 m away from the closest old patch. Recolonization of extinct patches was very rare. Small patches had the highest risk of extinction (5%) and, although floods can destroy even large populations, no large patches with flowering individuals became extinct. 4 Elasticity analysis indicated that the survival of patches made a much greater contribution to patch dynamics than the production of new patches. Increasing patch scale decreased the rates of colonization and extinction as well as the projected finite rates of increase in patch number, but elasticities remained invariant. 5 The river dynamics both create space for colonization and cause local extinctions, especially of small patches. The short-term dynamics of S. tatarica depend primarily on local dynamics but, in the long run, the species will track the availability of habitat, and its persistence will depend on a positive balance between colonization and extinction. 6 This species from a transient environment does not exhibit the extinction-recolonization dynamics predicted for metapopulations at equilibrium. The rate of the dynamics of plant species in relation to the rate of habitat changes may be one of the key determinants of their regional dynamics.

Aim: We investigated the phylogeographical history of a clonal-sexual orchid, to test the hypothesis that current patterns of genetic diversity and differentiation retain the traces of climatic fluctuations and of the species reproductive system. Location: Europe, Siberia and Russian Far East.Taxon: Cypripedium calceolus L. (Orchidaceae).Methods: Samples (>900, from 56 locations) were genotyped at 11 nuclear microsatellite loci and plastid sequences were obtained for a subset of them. Analysis of genetic structure and approximate Bayesian computations were performed.Species distribution modelling was used to explore the effects of past climatic fluctuations on the species range. Results: Analysis of genetic diversity reveals high heterozygosity and allele diversity, with no geographical trend. Three genetic clusters are identified with extant gene pools derived from ancestral demes in glacial refugia. Siberian populations exhibit different plastid haplotypes, supporting an early divergence for the Asian gene pool. Demographic results based on genetic data are compatible with an admixture event explaining differentiation in Estonia and Romania and they are consistent with past climatic dynamics inferred through species distribution modelling. Current population differentiation does not follow isolation by distance model and is compatible with a model of isolation by colonization. Main conclusions: The genetic differentiation observed today in C. calceolus preserves the signature of climatic fluctuations in the historical distribution range of the species. Our findings support the central role of clonal reproduction in the reducing loss of diversity through genetic drift. The dynamics of the clonal-sexual reproduction are responsible for the persistence of ancestral variation and stability during glacial periods and post-glacial expansion.