Size distribution and genetic structure in relation to clonal growth within a population of Magnolia tomentosa Thunb. (Magnoliaceae)

To establish a baseline for conservation of a threatened clonal tree, Magnolia tomentosa, we investigated size distribution and genetic structure within a population, using six microsatellite markers. Within the study site, 1044 living ramets (stems) were distinguished into 175 genets (individuals). The mean number of ramets per genet was 5.97, and 76% of all genets had multiple ramets. Genets, which apparently produced new ramets through sprouting and layering, were generally composed of several large ramets and many small ramets. Spatial autocorrelation analysis of microsatellite alleles revealed positive autocorrelation over short distances for both ramets and genets. The Moran's I-value of ramets in the shortest distance class was 3.8 times larger than that of genets, reflecting the effect of clonal growth. To analyse the size-class differences in genetic structure, the 175 genets were separated into two size classes, small and large. The correlogram for the small genets exhibited positive spatial autocorrelation in the shortest distance class, but this was not the case for the correlogram for the large genets, indicating that genetic structure is weakened or lost through self-thinning as the genets grow. The FIS value over all loci for the small genets was positive and deviated significantly from zero, while the corresponding value for the large genets was close to zero. The excess homozygotes in the small genets may be the result of genetic substructuring and/or inbreeding, and the reduction in homozygote frequency from the small to large genets may be because of loss of genetic structure and/or inbreeding depression.     

Dispersal patterns of Lonicera periclymenum determined by genetic analysis

Colonization of Lonicera periclymenum L. (honeysuckle) was studied by RAPD analysis of young ramets in two woodlots planted 20 years ago, and in all ramets in older woodlots within a range of 1 km. Mature ramets that climbed in a particular tree always belonged to one individual. Twenty-five percent of the mature individuals had reproduced vegetatively to other trees or patches nearby, which indicates that the larger part of reproduction is sexual. Some young plants that were growing at close distances from each other were genetically highly similar and shared high similarities to the same mature plants. They may be the product of one dispersal event. Detection of parents of young individuals by exclusion was not successful, because of the dominant nature of the bands. Average distances from young plants to genetically most similar mature plants were variable, due to the small number of colonization events. However, four ways of analysis of genetic similarity among all individuals indicated that exchange of genetic material by seed and pollen occurs to a large extent over small distances and within woodlots: (i) using the Mantel test, pairs of individuals with highest similarity were found significantly more often in the same woodlot than in different woodlots; (ii) genetic similarities between individuals decreased significantly with geographical distance, but only for distances up to 300 m; (iii) individuals of woodlots in the Western part of the study area were hardly related to individuals in the Eastern part of the study area, a distance of 2–3 km; (iv) Φ_ST in the study area was 0.186, indicating a limited gene flow between woodlots. These results are consistent with the dispersal distance as estimated from the average distance between colonized woodlots and the nearest occupied old woodlot in earlier research.     

Within-population genetic structure and clonal diversity of a threatened endemic metallophyte, Viola calaminaria (Violaceae)

We studied the within-population genetic structure and the clonality extent of Viola calaminaria, a rare endemic species of calamine soils, by means of RAPD markers in two populations (one recent and one ancient) with expected harsh and heterogeneous heavy-metal stress. At a very local scale (0.2-3 m), clonal propagation was detected in both populations, but the levels of clonal diversity were high (number of genets/number of ramets sampled = 0.9 [recent] and 0.76 [ancient]) and the maximal observed extension of the clones was 0.4 m. This indicated that clonality is not, for the species, an important mode of propagation and that clonal growth cannot be interpreted as a strategy for propagating or perpetuating adapted genotypes under harsh ecological constraints. Spatial autocorrelations revealed a significant (P < 0.001) negative value of correlogram slope in the two populations even when a single individual per clone was considered (i.e., analysis at the genet level). We conclude that spatial genetic structure at a very local scale reflects limited gene flow due to restricted seed dispersal rather than variation in clonal pattern in response to environmental heterogeneity. At a larger scale (2-30 m), spatial autocorrelations revealed a positive (P < 0.001) correlation at < 3 m and a random pattern at larger distances for the two populations. This suggested a patchy distribution of the genetically linked individuals associated with a disrupted pattern at a longer distance probably due to gene flow by pollen dispersal and a seed bank effect. The implications for the conservation of V. calaminaria are discussed.     

Clonal and spatial genetic structures of aspen (Populus tremuloides Michx.)

To portray aspen clonal and spatial genetic structures, we mapped and genotyped trees in two 1-ha plots, each containing three aspen cohorts originating from fire or subsequent secondary disturbances. We used four microsatellite loci to identify aspen clones and increment core analysis to determine tree age. Clonal dimensions were measured by the maximum distance between two ramets and the number of ramets per genet. Standard normal deviate (SND) was used to assess the spatial distribution of aspen genets and cohorts, and multivariate spatial genetic autocorrelations to assess the spatial distribution of aspen genetic variation. Most aspen genets consisted of only one ramet (> 75%). Median clonal dimensions were 19 and 29 m (maxima: 104 and 72 m in the two plots). No segregation was observed between clones. Aspen cohorts were spatially segregated but trees were spatially aggregated within old and medium-aged cohorts. In contrast, trees were more randomly distributed within the youngest cohorts. This coincided with a spatial genetic autocorrelation at small scales (up to 30 m) in the older cohorts and a more random genetic distribution in the youngest ones. Our results suggest that aspen spatial genetic structuring reflects the spatial patterns produced by the regeneration of discrete cohorts at different stages of succession. Vegetative reproduction leads to aspen genetic spatial structuring at small scales (few metres) until midsuccession. However, as the stand gets older, the spatial distribution of aspen trees and genetic structure evolve from a structured pattern to a more random one under a gap disturbances regime.     

A microsatellite-based estimation of clonal diversity and population subdivision in Zostera marina, a marine flowering plant

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 rho (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 (rho = 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 rho = 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.     

Clonal and fine-scale genetic structure in populations of a restricted Korean endemic, Hosta jonesii (Liliaceae) and the implications for conservation

BACKGROUND AND AIMS: In plant populations the magnitude of spatial genetic structure of apparent individuals (including clonal ramets) can be different from that of sexual individuals (genets). Thus, distinguishing the effects of clonal versus sexual individuals in population genetic analyses could provide important insights for evolutionary biology and conservation. To investigate the effects of clonal spread on the fine-scale spatial genetic structure within plant populations, Hosta jonesii (Liliaceae), an endemic species to Korea, was chosen as a study species. METHODS: Using allozymes as genetic markers, spatial autocorrelation analysis of ramets and of genets was conducted to quantify the spatial scale of clonal spread and genotype distribution in two populations of H. jonesii. KEY RESULTS: Join-count statistics revealed that most clones are significantly aggregated at < 3-m interplant distance. Spatial autocorrelation analysis of all individuals resulted in significantly higher Moran's I values at 0-3-m interplant distance than analyses of population samples in which clones were excluded. However, significant fine-scale genetic structure was still observed when clones were excluded. CONCLUSIONS: These results suggest that clones enhance the magnitude of spatial autocorrelation due to localized clonal spread. The significant fine-scale genetic structure detected in samples excluding clones is consistent with the biological and ecological traits exhibited by H. jonesii including bee pollination and limited seed dispersal. For conservation purposes, genetic diversity would be maximized in local populations of H. jonesii by collecting or preserving individuals that are spaced at least 5 m apart.     

竹叶眼子菜居群遗传多样性和克隆结构

采用ISSR技术对长江中游南岸豹澥湖和大冶湖不同生境中的竹叶眼子菜(Potamogeton malaianus)居群的遗传多样性及克隆结构进行了研究.结果表明,在两居群的106株个体中,利用6条ISSR引物共得到40条符合3/N标准并无连锁不平衡的清晰位点,竹叶眼子菜具有较高的遗传多样性,其多态位点百分率为75.0％,Shannon多样性指数为0.3736, 两居群的遗传分化很小.竹叶眼子菜的克隆多样性很高(D=0.9917),两居群间的克隆分化很大,不具有共有的基因型.竹叶眼子菜的基株分布为游击型构型,位于湖心的大冶居群克隆距离(3.0～31.5 m)明显地大于湖岸豹澥居群(2.4～6.7 m).     

Growth strategy of the stoloniferous rattan Calamus javensis in Mt. Halimun, Java

Calamus javensis is a widespread understorey rattan in Southeast Asia and is one of the dominant rattan species in Mt. Halimun National Park, West Java. This species can establish clumps either sexually with seeds or clonality with stolons. To analyze the role of sexual reproduction and clonality for clump establishment in C. javensis, we studied the vegetative and genetic structures of the population. Totals of 2,777 ramets comprising 1,321 clumps were found in three 0.16 ha plots. The number of ramets per clump showed reverse J-shaped distribution with a maximum of 15. Clustering and stoloniferous ramets accounted for 62 and 20% of all ramets, respectively. This indicates that C. javensis is actively engaged in clustering clonal growth. The longest stem was 14 m although 75% of all stems were shorter than 1 m long. The stolon ranged from 6 to 538 cm in length, which decreased the local density of ramets. Using randomly amplified polymorphic DNA (RAPD) analysis, we obtained 56 polymorphic bands for 118 clumps sampled from one of the plots. All samples showed different RAPD banding patterns, except one pair at a distance of 225 cm from each other. The genetic similarity among samples closer than 10 m was significantly higher than the expected value from a purely random distribution. These results suggest that most separate clumps are established by recruitment from seeds, and most seeds dispersed near mother plants. Hence, in C. javensis, clonality is more a growth strategy to increase the size of the genet than a dispersion-propagation strategy to expand the habitat.     

Genetic variation in Batrachospermum helminthosum (Batrachospermales, Rhodophyta) among and within stream reaches using intersimple sequence repeat molecular markers

Intersimple sequence repeat molecular markers were utilized to investigate the genetic relationship among individual gametophyte thalli of the freshwater red alga Batrachospermum helminthosum among distant stream reaches and within a stream reach. Fifteen thalli per stream reach were sampled from 11 streams throughout the known distribution in eastern North America from three locations in Ohio, and one location in Indiana, Michigan, North Carolina, Tennessee, Louisiana, Rhode Island, Massachusetts and Connecticut. The pairwise φ_ST analysis showed significant genetic differences (P<0.05) among all streams. The partitioning of genetic variation was almost equal within and among streams (45% and 55%, respectively). Genetic variation among populations did not reflect geographic distance, suggesting that long distance dispersal may be important in the distribution of this alga. Fifty‐eight individuals from Five Mile Creek, Ohio, were investigated from three distinct segments of the stream (upstream, middle and downstream) to examine small‐scale genetic variation within a stream reach. A much higher proportion of genetic variation was observed within a stream segment (79%) than among the three segments (21%). Among these stream segments within Five Mile Creek, the individuals were variously related, with genetic similarity and spatial distance uncorrelated. A similar result was obtained among individuals within other stream reaches, suggesting that genetic structure within a stream reach may be more complex than just reproduction among closely located individuals.     

GENE FLOW IN CHAMAECRISTA FASCICULATA (LEGUMINOSAE) II. GENE ESTABLISHMENT

The role of gene establishment in gene flow was investigated in a population of the annual legume Chamaecrista fasciculata by determining the effect of interparent distance on progeny fitness throughout the entire life history. A decelerating gain in progeny fitness with increasing interparent distance was observed. Selfed progeny suffered a 2-fold fitness disadvantage compared to progeny derived from mating events between individuals in the same neighborhood. Progeny derived from within neighborhood crosses had lower fitness than progeny from crosses between neighborhoods. Coupling the effect of interparent distance on gene establishment with information on gene dispersal resulted in a considerable increase in estimated gene flow. However, gene flow was still limited, as the average neighborhood area corresponded to a circle with radius of approximately 3.0 m. Yearly fluctuations in population size and variation in reproductive output lowered the estimate of N_e below the census estimate to approximately 100 individuals. The role of a seed bank in increasing the estimate of N_e was found to be insignificant. It is likely that genetic drift plays a major role in determining the distribution of genetic variation in this population.     

Detection and visualization of spatial genetic structure in continuous Eucalyptus globulus forest

Visualizing the pattern of variation using microsatellites within a Eucalyptus globulus forest on the island of Tasmania provided surprising insights into the complex nature of the fine-scale spatial genetic structure that resides in these forests. We used spatial autocorrelation and principal coordinate analysis to compare fine-scale genetic structure between juvenile and mature cohorts in a study area, 140 m in diameter, located within a typical, continuous E. globulus forest. In total, 115 juvenile and 168 mature individuals were genotyped with eight highly polymorphic microsatellite loci. There was no significant difference in the level of genetic diversity between cohorts. However, there were differences in the spatial distribution of the genetic variation. Autocorrelation analysis provided clear evidence for significant spatial genetic structure in the mature cohort and significant, but weaker, structure in the juvenile cohort. The spatial interpolation of principal coordinate axes, derived from ordination of the genetic distance matrix between individuals, revealed a spatially coherent family group which was evident in both cohorts. Direct comparison of the genetic structure within each cohort allowed visualization of a shift in the spatial distribution of genetic variation within the population of approximately 10 m. As the shift coincided with the direction of prevailing winds, it is hypothesized that this phenomenon is due to downwind dispersal of seeds and is indicative of the important role of prevailing winds in forcing eastward gene flow in these high-latitude forests.     

Relatedness structure in Rhododendron metternichii var. hondoense revealed by microsatellite analysis

The relatedness structure of Rhododendron metternichii Sieb. et Zucc. var. hondoense Nakai was analysed in a 150 x 70-m quadrat in Hiroshima Prefecture, western Japan. The population of R. metternichii occurred as three subpopulations at the study site (A1-A3). Pairwise relatedness based on microsatellite genotypes at eight loci and Mantel tests revealed a hierarchical structure of relatedness within and among subpopulations: (i) relatedness between individuals within 10 m of one another was significantly positive; (ii) relatedness between individuals in the same subpopulation was significantly positive, but negative between individuals in distant subpopulations; and (iii) relatedness was not significantly different from zero among neighbouring subpopulations. In detail, however, relatedness within each subpopulation was significantly positive in subpopulation A1, relatively weak but significantly positive in subpopulation A2, and not significantly different from zero in subpopulation A3. Relatedness within each subpopulation was inversely related to correlations between interindividual distance and relatedness. The aggregation of related individuals at short distances from one another may lead to decreasing relatedness within subpopulations as a whole. Moreover, negative correlations between interindividual distance and relatedness corresponded to high flowering densities at less than 10-m distance, implying that high flowering densities reduce pollinator foraging distance and lead to stronger genetic structure within subpopulations. Small individuals (< 2.0 m in height) showed stronger genetic structure compared with that of large individuals (> or = 2.0 m in height). The different relatedness structure within and among subpopulations may be caused by various degrees of gene flow affected by distribution patterns of individuals and population density.     

Genetic differentiation in the Agave deserti (Agavaceae) complex of the Sonoran desert

The Agave deserti complex, comprising A. deserti, A. cerulata and A. subsimplex, represents a group of species and subspecies with a near allopatric distribution and clear differences in morphology. Genetic differentiation and taxonomic status with respect to spatial distribution of 14 populations of the complex were analyzed in an effort to understand the evolution and speciation process within the genus. Allelic frequencies, levels of genetic variation, expected heterozygosity (H(S)), proportion of polymorphic loci (P), and genetic differentiation (theta and Nei's genetic distance) were estimated using 41 putative RAPD loci. All three species show high levels of genetic variation (H(S)=0.12-0.29, P=63.4-95.1), and low genetic differentiation between populations and species (theta populations=0.14+/-0.02 (SE); G(st)=0.11+/-0.02). Accordingly, gene flow among populations was estimated as high by three different methods (N(m)=2.91-6.14). Nei's genetic distances between the three species were low compared to the values obtained from other Agavaceae, and there was no clear correlation with taxonomic divisions. In a UPGMA analysis, A. subsimplex and A. cerulata formed exclusive monospecific clusters, whereas the A. deserti populations appear in more than one cluster together with other species. The results were consistent with a pattern of genetic isolation by distance.     

Effects of crossing distance and genetic relatedness on pollen performance in Alstroemeria aurea (Alstroemeriaceae)

Prezygotic barriers may represent effective mechanisms to avoid the deleterious effects of inbreeding. This study reports the existence of distance-dependent prezygotic barriers in self-compatible Alstroemeria aurea, a clonal herb native to temperate forests of the southern Andes. We analyzed pollen germination and tube growth as indicators of donor-recipient affinity using crossing distances of 1, 10, and 100 m. We used allozyme electrophoresis to determine the actual genetic relatedness between donor and recipient ramets. Pollen germination was not affected by distance between mates, but the number of pollen tubes reaching the base of the style increased strongly with distance between donor and recipient. This pattern was related to an increase in genetic dissimilarity with distance between mates. In contrast, pollen tube-style interactions did not change with distance when we restricted analysis to individuals at different distances that appeared to be genetically identical. This test implied genetic dissimilarity as the critical factor affecting pollen performance. We propose that the existence of prezygotic barriers might contribute to the high degree of genetic mixing exhibited by some clonal species.     

A Comprehensive Study of Genic Variation in Natural Populations of Drosophila melanogaster. II. Estimates of Heterozygosity and Patterns of Geographic Differentiation

A study of genic variation in natural population of D. melanogaster was undertaken (1) to obtain a better estimate of heterozygosity by sampling a relatively large number of gene loci and (2) to identify different groups of polymorphic loci whose variation patterns might suggest different kinds of selection forces. A total of 117 gene loci (coding for 79 enzymes and 38 abundant proteins) were studied in 15 geographically distant populations originating from different continents. The findings of this study are as follows: (1) of the 117 gene loci studied, 61 are polymorphic and 56 are uniformly monomorphic everywhere. (2) An average population is polymorphic for 43% of its gene loci and an average individual is heterozygous for 10% of its gene loci. These estimates are remarkably similar among populations. (3) The average within-locality heterozygosity (H(S)) for polymorphic loci is uniformly distributed over the range of heterozygosity observed; i.e. , given that a locus has any local variation, it is nearly as likely to have a lot as a little. (4) The distribution of F(ST) (fixation index) is strongly skewed, with a prominent mode at 8-10% and a long tail of high values reaching a maximum of 58%. Two-thirds of all loci fall within the bell-shaped distribution centered on an F(ST) of 8-10%, a result compatible with the notion that they are experiencing a common tendency toward small interlocality differences owing to extensive gene flow among populations. (5) The distribution of total heterozygosity (H(T)) has a prominent bimodal distribution. The lower mode consists of loci with single prominent allele and a few uncommon ones and the upper mode consists of clinally varying loci with a high F(ST ) (e.g., Adh and G6-pd), loci with many alleles in high frequency (e.g., Ao and Xdh) and loci with two alleles in high frequency in all populations but, with little interpopulational differentiation (e.g., Est-6 and alpha-Fuc). The loci in the lower mode are probably under purifying selection; a large proportion of those in the latter mode may be under balancing selection. (6) Comparison of genic variation for loci located inside vs. outside inversions, comparison of F(ST) for inversions and their associated genes, and comparison of F(ST) and map position for pairs of loci all suggest that, while linkage has some influence, it does not seem to constrain the pattern of variation that a locus may develop. (7) Eighteen polymorphic loci show latitudinal variation in allele frequencies which are consistent in populations from different continents. (8) Estimates of Nei genetic distance between population pairs are generally low between populations on the same continent and high between populations on different continents. There are two important exceptions: population pairs for which both localities are in the temperate zone show no relationship to distance, and in cases where both populations are tropical or subtropical, the genetic distance is higher than for the temperate-tropical comparisons and seem even higher than one would expect from the geographic distance separating them. The latter observation suggests that either geographic separation outweighs differences in environment in determining the genetic composition of a population or that all tropical populations are not experiencing the same environment.-The results are discussed in relation to the neutralist-selectionist controversy of genic variation and two important conclusions are drawn: First, there is a negative correlation between the number of loci sampled and the resulting heterozygosity. This means that available estimates of heterozygosity, 85% of which are based on 30 or fewer loci, are high and hence not appropriate for making between-taxa comparisons. Secondly, there is a group of loci, comprising one-third of polymorphic loci (or about 15% of all loci studied), that is distinguishable by different patterns of variation within and among populations. Most of these loci have clinal variation which is consistent with the hypothesis that their genetic variation is maintained by balancing selection.     

Genetic variation in wild sorghum (Sorghum bicolor ssp. verticilliflorum (L.) Moench) germplasm from Ethiopia assessed by random amplified polymorphic DNA (RAPD)

The extent and distribution of genetic variation in wild sorghum (Sorghum bicolor ssp. verticilliflorum (L.) Moench) collected from five different geographical regions in Ethiopia were analyzed using random amplified polymorphic DNA (RAPD) markers for 93 individuals representing 11 populations. Nine decamer primers generated a total of 83 polymorphic bands with 8-12 bands per primer and a mean of 9 bands across the 93 individuals. The amount of genetic variation among the populations (H = 0.37) and among the geographical region (H = 0.44) was low to moderate, despite the high degree of polymorphic bands per primer. Similarly, the mean genetic distance (0.08) among populations as well as among regions of origin (0.04) of the population was found to be low. The low genetic variation may be due to the reduced population size of the wild sorghum in Ethiopia because of habitat change. Partitioning of the genetic variation into between and within the population as well as between and within the regions of origin revealed that 75% and 88% of the variation was found within the populations and within the regions, respectively. Cluster analysis of genetic distance estimates further confirmed low level of differentiation of wild sorghum populations both on population and regional bases. The implications of the results for genetic conservation purposes are discussed.     

Evolution of sprouting versus seeding inAspalathus linearis

We have tested the hypothesis that reseeding is a plesiomorphic character state and that sprouting is a derived state inAspalathus linearis, and that the latter is an adaptation to ensure fire-survival in a fireprone environment. Samples of five seeder and four sprouter populations of A.linearis were examined by horizontal starch gel electrophoresis to assess the amount of genetic differentiation within and between sprouting and seeding populations, and to determine the extent of gene flow between the populations. Leaf extracts were surveyed for ten enzymes and gene products revealed genetic variation at 13 (76%) of 17 protein coding loci. Allele frequency differences were found between sprouting and seeding populations and genetic distance values show that the sprouters are grouped separate from the seeders, thus providing support for the morphological data on which the above mentioned hypothesis is based. It is evident that evolution operates at the population level inA. linearis.     

Clone identification and clonal structure of the European aspen (Populus tremula)

The European aspen (Populus tremula) is thought to reproduce mostly asexually. Thus aspen forms clones, in which several ramets belong to one genetically defined genet. We compared the clonal structure of aspen in old-growth and managed forests in southern and northeastern Finland. Clones were identified using morphological characters and nine microsatellite loci originally developed for Populus tremuloides. There were more clones identified by microsatellites than morphotypes both in old-growth and managed forest. The average size of the clones was only 2.3 ramets and most clones (70%) consisted of just one ramet. The size of the clones showed no difference between managed and old-growth forests or between northeastern and southern Finland. The small size of the clones suggests that most of them are relatively young. Therefore, sexual reproduction may be more common than previously thought. There was an aggregated spatial genetic structure as measured by Moran's I (0-10 m) and by co-ancestry (rho(ij), 0-20 m). Low level of co-ancestry can be explained by relatively unrestricted gene flow, the important role of disturbance in reproduction, and/or local selection.     

Species-specific sprouting pattern in two dioecious Lindera shrubs: The role of physiological integration

Sprouting is recognized as an important genet persistence strategy for clonal woody plants, but the role of sprouting may differ between species and between sexes, depending on physiological integration. We tested the effect of physiological integration on the mortality, recruitment and growth of the sprouting male and female ramets of two closely related dioecious shrubs of Lindera, in a field experiment using girdling manipulation. Although between-sex differences observed were obscure, we found between-species differences in the sprouting patterns. The rates of ramet mortality and recruitment were significantly lower for L. praecox than L. triloba. In L. praecox genets, the ramet production was low, and the main ramets might actively translocate assimilates towards the small sprouted ramets, which then facilitates high ramet growth and survival (sprout-nursing strategy). Meanwhile, in L. triloba genets, although many ramets were recruited, assimilate translocation from the main ramets to the sprouted ramets might be less abundant, which causes high ramet mortality (sprout-turnover strategy). For a more general knowledge of the various sprouting strategies in clonal plants, our study demonstrated that inter-specific comparisons using girdling experiments at the whole-plant level could reveal the role of physiological integration on the link between the sprouting pattern and above-ground structures of clonal plants.