Spatial genetic structure and clonal diversity of island populations of lady's slipper (Cypripedium calceolus) from the Biebrza National Park (northeast Poland)

Transcriptome data reveals the conservation genetics of Cypripedium forrestii, a plant species with extremely small populations endemic to Yunnan, China

The Cypripedium forrestii is an orchid species with extremely small populations (PSESP) in Yunnan, China. C. forrestii is range-restricted and less-studied than many orchid species, and it is exposed to various threats to its survival. We investigated its potential habitats and collected 52 samples from eight locations, as well as two outgroup species for reference. We developed genetic markers (SNPs) for C. forrestii based on transcriptome sequencing (RNA-seq) data, and analyzed the genetic diversity, population structure, gene flow and demographic history of C. forrestii in detail. C. forrestii is a taxonomically independent species to protect. We found that the genetic diversity of C. forrestii was very low (1.7e-4) compared with other endangered species. We identified three genetic clusters, and several populations with distinct genetic backgrounds. Most genetic diversity was found within sampling sites (87.87%) and genetic clusters (91.39%). Gene flow has been greatly limited over the most recent generations, probably due to geographical distance, historical climate change and habitat fragmentation. We also detected a severe bottleneck event brought about by the recent population constraints. These factors, together with its reproductive characteristics, contribute to the population fragmentation and low genetic diversity of C. forrestii. Based on our findings, we suggest an integrative conservation strategy to protect and recover the genetic diversity of C. forrestii and a further comprehensive study of its ecological traits in the future.

Effective population size in a partially clonal plant is not predicted by the number of genetic individuals

Estimating effective population size (N _e) is important for theoretical and practical applications in evolutionary biology and conservation. Nevertheless, estimates of N _e in organisms with complex life-history traits remain scarce because of the challenges associated with estimation methods. Partially clonal plants capable of both vegetative (clonal) growth and sexual reproduction are a common group of organisms for which the discrepancy between the apparent number of individuals (ramets) and the number of genetic individuals (genets) can be striking, and it is unclear how this discrepancy relates to N _e. In this study, we analysed two populations of the orchid Cypripedium calceolus to understand how the rate of clonal versus sexual reproduction affected N _e. We genotyped >1000 ramets at microsatellite and SNP loci, and estimated contemporary N _e with the linkage disequilibrium method, starting from the theoretical expectation that variance in reproductive success among individuals caused by clonal reproduction and by constraints on sexual reproduction would lower N _e. We considered factors potentially affecting our estimates, including different marker types and sampling strategies, and the influence of pseudoreplication in genomic data sets on N _e confidence intervals. The magnitude of N _e/N _ramets and N _e/N _genets ratios we provide may be used as reference points for other species with similar life-history traits. Our findings demonstrate that N _e in partially clonal plants cannot be predicted based on the number of genets generated by sexual reproduction, because demographic changes over time can strongly influence N _e. This is especially relevant in species of conservation concern in which population declines may not be detected by only ascertaining the number of genets.

Soil properties and plant species can predict population size and potential introduction sites of the endangered orchid Cypripedium calceolus

Background and Aims

To counteract the ongoing worldwide biodiversity loss, conservation actions are required to re-establish populations of threatened species. Two key factors predominantly involved in finding the most suitable habitats for endangered plant species are the surrounding plant community composition and the physicochemical parameters of the soil rooting zone. However, such factors are likely to be context- and species-dependent, so it remains unclear to what extent they influence the performance of target species.

Methods

We studied large and small Swiss populations of the endangered orchid Cypripedium calceolus. We measured functional traits related to C. calceolus plant and population performance (clonal patch area, plant height, number, of leaf, stems, flowers and fruits), realized vegetation surveys, soil profile analyses, and tested for relationships between plant traits and the surrounding vegetation structure or soil physicochemical parameters.

Results

Large populations contained bigger patches with more stems and leaves, and produced more flower per individual than small populations. Neither vegetation alliances nor soil classes per se could predict C. calceolus functional traits and population size. However, functional traits explaining population performance and size were related to specific soil parameters (soil organic matter content, pH and phosphorus), in addition to a combination of presence-absence of plant indicator species, relating to ecotones between forests and clearings.

Conclusion

We show that even for species that can grow across a wide range of vegetation groups both indicator species and specific soil parameters can be used to assess the most favourable sites to implement (re)-introduction actions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11104-023-05945-4.

The evolutionary history of Cardamine bulbifera shows a successful rapid postglacial Eurasian range expansion in the absence of sexual reproduction

BACKGROUND AND AIMS

Sexual reproduction is known to drive plant diversification and adaptation. Here we investigate the evolutionary history and spatiotemporal origin of a dodecaploid (2n = 12x = 96) Eurasian deciduous woodland species, Cardamine bulbifera, which reproduces and spreads via vegetative bulb-like structures only. The species has been among the most successful range-expanding understorey woodland plants in Europe, which raises the question of the genetic architecture of its gene pool, since its hexaploid (2n = 6x = 48) but putatively outcrossing closest relative, C. quinquefolia, displays a smaller distribution range in Eastern Europe towards the Caucasus region. Cardamine bulbifera belongs to a small monophyletic clade of four species comprising also C. abchasica (2n = 2x = 16) and C. bipinnata (unknown ploidy) from the Caucasus region.

METHODS

We sequenced the genomes of the two polyploids and their two putative ancestors using Illumina short-read sequencing technology (×7-8 coverage). Covering the entire distribution range, genomic data were generated for 67 samples of the two polyploids (51 samples of C. bulbifera, 16 samples of C. quinquefolia) and 6 samples of the putative diploid taxa (4 samples of C. abchasica, 2 samples of C. bipinnata) to unravel the evolutionary origin of the polyploid taxa using phylogenetic reconstructions of biparentally and maternally inherited genetic sequence data. Ploidy levels of C. bulbifera and C. quinquefolia were analysed by comparative chromosome painting. We used genetic assignment analysis (STRUCTURE) and approximate Bayesian computation (ABC) modelling to test whether C. bulbifera represents genetically differentiated lineages and addressed the hypothesis of its hybrid origin. Comparative ecological modelling was applied to unravel possible niche differentiation among the two polyploid species.

KEY RESULTS

Cardamine bulbifera was shown to be a non-hybridogenous, auto-dodecaploid taxon of early Pleistocene origin, but with a history of past gene flow with its hexaploid sister species C. quinquefolia, likely during the last glacial maximum in shared refuge areas in Eastern Europe towards Western Turkey and the Crimean Peninsula region. The diploid Caucasian endemic C. abchasica is considered an ancestral species, which also provides evidence for the origin of the species complex in the Caucasus region. Cardamine bulbifera successfully expanded its distribution range postglacially towards Central and Western Europe accompanied by a transition to exclusively vegetative propagation.

CONCLUSIONS

A transition to vegetative propagation in C. bulbifera is hypothesized as the major innovation to rapidly expand its distribution range following postglacially progressing woodland vegetation throughout Europe. Preceding and introgressive gene flow from its sister species C. quinquefolia in the joint refuge area is documented. This transition and ecological differentiation may have been triggered by preceding introgressive gene flow from its sister species in the joint East European refuge areas.

Genetic diversity may help evolutionary rescue in a clonal endemic plant species of Western Himalaya

Habitat loss due to climate change may cause the extinction of the clonal species with a limited distribution range. Thus, determining the genetic diversity required for adaptability by these species in sensitive ecosystems can help infer the chances of their survival and spread in changing climate. We studied the genetic diversity and population structure of Sambucus wightiana-a clonal endemic plant species of the Himalayan region for understanding its possible survival chances in anticipated climate change. Eight polymorphic microsatellite markers were used to study the allelic/genetic diversity and population structure. In addition, ITS1-ITS4 Sanger sequencing was used for phylogeny and SNP detection. A total number of 73 alleles were scored for 37 genotypes at 17 loci for 8 SSRs markers. The population structural analysis using the SSR marker data led to identifying two sub-populations in our collection of 37 S. wightiana genotypes, with 11 genotypes having mixed ancestry. The ITS sequence data show a specific allele in higher frequency in a particular sub-population, indicating variation in different S. wightiana accessions at the sequence level. The genotypic data of SSR markers and trait data of 11 traits of S. wightiana, when analyzed together, revealed five significant Marker-Trait Associations (MTAs) through Single Marker Analysis (SMA) or regression analysis. Most of the SSR markers were found to be associated with more than one trait, indicating the usefulness of these markers for working out marker-trait associations. Moderate to high genetic diversity observed in the present study may provide insurance against climate change to S. wightiana and help its further spread.

Genetic History of the Remnant Population of the Rare Orchid Cypripedium calceolus Based on Plastid and Nuclear rDNA

The lady’s slipper orchid (Cypripedium calceolus), which inhabits shady deciduous and mixed forests and meadows, is now threatened with extinction in many European countries, and its natural populations have been dramatically declining in recent years. Knowledge of its evolutionary history, genetic variability, and processes in small populations are therefore crucial for the species’ protection. Nowadays, in south-west Poland, it is only distributed in seven small remnant and isolated populations, which we examined. One nuclear (ITS rDNA) and two plastid (accD-psa1, trnL-F) markers were analyzed and compared globally in this study. Based on the nuclear marker, the most common ancestor of C. calceolus and Cypripedium shanxiense existed about 2 million years ago (95% HPD: 5.33–0.44) in Asia. The division of the C. calceolus population into the European and Asian lineages indicated by C/T polymorphism started about 0.5 million years ago (95% HPD: 1.8–0.01). The observed variation of plastid DNA, which arose during the Pleistocene glacial–interglacial cycles, is still diffuse in Poland. Its distribution is explained by the result of fragmentation or habitat loss due to human impact on the environment.

Genetic variation and population structure of clonal Zingiber zerumbet at a fine geographic scale: a comparison with two closely related selfing and outcrossing Zingiber species

BACKGROUND

There has always been controversy over whether clonal plants have lower genetic diversity than plants that reproduce sexually. These conflicts could be attributed to the fact that few studies have taken into account the mating system of sexually reproducing plants and their phylogenetic distance. Moreover, most clonal plants in these previous studies regularly produce sexual progeny. Here, we describe a study examining the levels of genetic diversity and differentiation within and between local populations of fully clonal Zingiber zerumbet at a microgeographical scale and compare the results with data for the closely related selfing Z. corallinum and outcrossing Z. nudicarpum. Such studies could disentangle the phylogenetic and sexually reproducing effect on genetic variation of clonal plants, and thus contribute to an improved understanding in the clonally reproducing effects on genetic diversity and population structure.

RESULTS

The results revealed that the level of local population genetic diversity of clonal Z. zerumbet was comparable to that of outcrossing Z. nudicarpum and significantly higher than that of selfing Z. corallinum. However, the level of microgeographic genetic diversity of clonal Z. zerumbet is comparable to that of selfing Z. corallinum and even slightly higher than that of outcrossing Z. nudicarpum. The genetic differentiation among local populations of clonal Z. zerumbet was significantly lower than that of selfing Z. corallinum, but higher than that of outcrossing Z. nudicarpum. A stronger spatial genetic structure appeared within local populations of Z. zerumbet compared with selfing Z. corallinum and outcrossing Z. nudicarpum.

CONCLUSIONS

Our study shows that fully clonal plants are able not only to maintain a high level of within-population genetic diversity like outcrossing plants, but can also maintain a high level of microgeographic genetic diversity like selfing plant species, probably due to the accumulation of somatic mutations and absence of a capacity for sexual reproduction. We suggest that conservation strategies for the genetic diversity of clonal and selfing plant species should be focused on the protection of all habitat types, especially fragments within ecosystems, while maintenance of large populations is a key to enhance the genetic diversity of outcrossing species.

Genetic Diversity and Conservation Status of Helianthus verticillatus, an Endangered Sunflower of the Southern United States

Evaluating species diversity and patterns of population genetic variation is an essential aspect of conservation biology to determine appropriate management strategies and preserve the biodiversity of native plants. Habitat fragmentation and potential habitat loss are often an outcome of a reduction in naturally occurring wildfires and controlled prescribed burning, as seen in Helianthus verticillatus (whorled sunflower). This endangered, wild relative of the common sunflower, Helianthus annuus, is endemic to four locations in Alabama, Georgia, and Tennessee, United States. Despite its endangered status, there is no recovery plan for H. verticillatus, and knowledge related to its basic plant biology and importance in ecosystem services is mostly unknown. In this study, we utilized 14 microsatellite loci to investigate fine-scale population structure and genetic diversity of H. verticillatus individuals found on two sampling sites within the Georgia population. Our results indicated moderate genetic diversity and the presence of two distinct genetic clusters. Analyses of molecular variance indicated that the majority of variance was individually based, thus confirming high genetic differentiation and limited gene flow between H. verticillatus collection sites. The evidence of a population bottleneck in these sites suggests a recent reduction in population size that could be explained by habitat loss and population fragmentation. Also, high levels of linkage disequilibrium were detected, putatively suggesting clonal reproduction among these individuals. Our study provides a better understanding of fine-scale genetic diversity and spatial distribution of H. verticillatus populations in Georgia. Our results can underpin an original recovery plan for H. verticillatus that could be utilized for the conservation of this endangered species and to promote its persistence in the wild.

Rare sex or out of reach equilibrium? The dynamics of F IS in partially clonal organisms

BACKGROUND

Partially clonal organisms are very common in nature, yet the influence of partial asexuality on the temporal dynamics of genetic diversity remains poorly understood. Mathematical models accounting for clonality predict deviations only for extremely rare sex and only towards mean inbreeding coefficient [Formula: see text]. Yet in partially clonal species, both F IS  < 0 and F IS  > 0 are frequently observed also in populations where there is evidence for a significant amount of sexual reproduction. Here, we studied the joint effects of partial clonality, mutation and genetic drift with a state-and-time discrete Markov chain model to describe the dynamics of F IS over time under increasing rates of clonality.

RESULTS

Results of the mathematical model and simulations show that partial clonality slows down the asymptotic convergence to F IS  = 0. Thus, although clonality alone does not lead to departures from Hardy-Weinberg expectations once reached the final equilibrium state, both negative and positive F IS values can arise transiently even at intermediate rates of clonality. More importantly, such "transient" departures from Hardy Weinberg proportions may last long as clonality tunes up the temporal variation of F IS and reduces its rate of change over time, leading to a hyperbolic increase of the maximal time needed to reach the final mean [Formula: see text] value expected at equilibrium.

CONCLUSION

Our results argue for a dynamical interpretation of F IS in clonal populations. Negative values cannot be interpreted as unequivocal evidence for extremely scarce sex but also as intermediate rates of clonality in finite populations. Complementary observations (e.g. frequency distribution of multiloci genotypes, population history) or time series data may help to discriminate between different possible conclusions on the extent of clonality when mean [Formula: see text] values deviating from zero and/or a large variation of F IS over loci are observed.

Microsatellite-based genetic diversity patterns in disjunct populations of a rare orchid

We investigated the patterns of genetic diversity and structure in seven disjunct populations of a rare North American orchid, Cypripedium kentuckiense by including populations that represented the periphery and the center of the its range. Eight nuclear and two chloroplast microsatellites were used. Genetic diversity was low across the sampled populations of C. kentuckiense based on both nuclear (average An = 4.0, Ho = 0.436, He = 0.448) and cpDNA microsatellites (average An = 1.57, Nh = 1.57 and H = 0.133). The number of private alleles ranged from one to four per population with a total of 17 private alleles detected at five nuclear microsatellites. One private allele at one cpDNA microsatellite was also observed. Although the absolute values for nuclear microsatellite based population differentiation were low (Fst = 0.075; ϕPT = 0.24), they were statistically significant. Pairwise Fst values ranged from 0.038 to 0.123 and each comparison was significant. We also detected isolation by distance with nDNA microsatellites based on the Mantel test (r(2) = 0.209, P = 0.05). STRUCTURE analysis and the neighbor joining trees grouped the populations similarly whereby the geographically proximal populations were genetically similar. Our data indicate that the species is genetically depauperate but the diversity is distributed more or less equally across its range. Population differentiation and isolation by distance were detectable, which indicates that genetic isolation is beginning to manifest itself across the range in this rare species.

Effects of population structure on pollen flow, clonality rates and reproductive success in fragmented Serapias lingua populations

BACKGROUND

Fragmentation of habitats by roads, railroads, fields, buildings and other human activities can affect population size, pollination success, sexual and asexual reproduction specially in plants showing pollinator limitation, such as Mediterranean orchids. In this study, we assessed pollen flow, selfing rates, vegetative reproduction and female reproductive success and their correlations with habitat characters in nine fragmented subpopulations of Serapias lingua. To improve understanding of population structure effects on plant biology, we examined genetic differentiation among populations, pollen flow, selfing rates and clonal reproduction using nuclear microsatellite markers.

RESULTS

Smaller populations showed a significant heterozygote deficit occurred at all five nuclear microsatellite loci, the coefficient of genetic differentiation among populations was 0.053 and pairwise FST was significantly correlated with the geographical distance between populations. Paternity analysis of seeds showed that most pollen flow occurred within a population and there was a positive correlation between percentage of received pollen and distance between populations. The fruit production rate varied between 5.10 % and 20.30 % and increased with increasing population size, while the percentage of viable seeds (78-85 %) did not differ significantly among populations. The extent of clonality together with the clonal and sexual reproductive strategies varied greatly among the nine populations and correlated with the habitats where they occur. The small, isolated populations tended to have high clonal diversity and low fruit production, whereas the large populations with little disturbance were prone to have reductions in clonal growth and increased sexual reproduction.

CONCLUSIONS

We found that clonality offers an advantage in small and isolated populations of S. lingua, where clones may have a greater ability to persist than sexually reproducing individuals.

Clonality as a driver of spatial genetic structure in populations of clonal tree species

Random genetic drift, natural selection and restricted gene dispersal are basic factors of the spatial genetic structure (SGS) in plant populations. Clonal reproduction has a profound effect on population dynamics and genetic structure and thus emerges as a potential factor in contributing to and modelling SGS. In order to assess the impact of clonality on SGS we studied clonal structure and SGS in the population of Populus alba. Six hundred and seventy-two individuals were mapped and genotyped with 16 nuclear microsatellite markers. To answer the more general question regarding the relationship between SGS and clonality we used Sp statistics, which allows for comparisons of the extent of SGS among different studies, and the comparison of published data on SGS in clonal and non-clonal tree species. Sp statistic was extracted for 14 clonal and 27 non-clonal species belonging to 7 and 18 botanical families, respectively. Results of genetic investigations conducted in the population of P. alba showed over-domination of clonal reproduction, which resulted in very low clonal diversity (R = 0.12). Significant SGS was found at both ramet (Sp = 0.095) and genet level (Sp = 0.05) and clonal reproduction was indicated as an important but not sole driving factor of SGS. Within-population structure, probably due to family structure also contributed to high SGS. High mean dominance index (D = 0.82) indicated low intermingling among genets. Literature survey revealed that clonal tree species significantly differ from non-clonal species with respect to SGS, having 2.8-fold higher SGS. This led us to conclude that clonality is a life-history trait that can have deep impact on processes acting in populations of clonal tree species leading to significant SGS.

Is gene flow the most important evolutionary force in plants?

Although theory has demonstrated rather low levels of gene flow are sufficient to counteract opposing mutation, drift, and selection, widespread recognition of the evolutionary importance of gene flow has come slowly. The perceived role of gene flow as an evolutionary force has vacillated over the last century. In the last few decades, new methods and analyses have demonstrated that plant gene flow rates vary tremendously-from nil to very high-depending on the species and specific populations involved, and sometimes over time for individual populations. In many cases, the measured gene flow rates are evolutionarily significant at distances of hundreds and sometimes thousands of meters, occurring at levels sufficient to counteract drift, spread advantageous alleles, or thwart moderate levels of opposing local selection. Gene flow in plants is likely to often act as a cohesive force, uniting individual plant species into real evolutionary units. Also, gene flow can evolve under natural selection, decreasing or increasing. The fact of frequent, but variable, plant gene flow has important consequences for applied issues in which the presence or absence of gene flow might influence the outcome of a policy, regulatory, or management decision. Examples include the unintended spread of engineered genes, the evolution of invasiveness, and conservation. New data-rich genomic techniques allow closer scrutiny of the role of gene flow in plant evolution. Most plant evolutionists now recognize the importance of gene flow, and it is receiving increased recognition from other areas of plant biology as well.

A review of the allozyme data set for the Canarian endemic flora: causes of the high genetic diversity levels and implications for conservation

Background and Aims Allozyme and reproductive data sets for the Canarian flora are updated in order to assess how the present levels and structuring of genetic variation have been influenced by the abiotic island traits and by phylogenetically determined biotic traits of the corresponding taxa; and in order to suggest conservation guidelines. Methods Kruskal-Wallis tests are conducted to assess the relationships of 27 variables with genetic diversity (estimated by A, P, Ho and He) and structuring (GST) of 123 taxa representing 309 populations and 16 families. Multiple linear regression analyses (MLRAs) are carried out to determine the relative influence of the less correlated significant abiotic and biotic factors on the genetic diversity levels. Key Results and Conclusions The interactions between biotic features of the colonizing taxa and the abiotic island features drive plant diversification in the Canarian flora. However, the lower weight of closeness to the mainland than of (respectively) high basic chromosome number, partial or total self-incompatibility and polyploidy in the MLRAs indicates substantial phylogenetic constraint; the importance of a high chromosome number is feasibly due to the generation of a larger number of linkage groups, which increase gametic and genotypic diversity. Genetic structure is also more influenced by biotic factors (long-range seed dispersal, basic chromosome number and partial or total self-incompatibility) than by distance to the mainland. Conservation-wise, genetic structure estimates (FST/GST) only reflect endangerment under intensive population sampling designs, and neutral genetic variation levels do not directly relate to threat status or to small population sizes. Habitat protection is emphasized, but the results suggest the need for urgent implementation of elementary reproductive studies in all cases, and for ex situ conservation measures for the most endangered taxa, even without prior studies. In non-endangered endemics, multidisciplinary research is needed before suggesting case-specific conservation strategies. The molecular information relevant for conservation should be conserved in a standardized format to facilitate further insight.

Effects of clonality on the genetic variability of rare, insular species: the case of Ruta microcarpa from the Canary Islands

Many plant species combine sexual and clonal reproduction. Clonal propagation has ecological costs mainly related to inbreeding depression and pollen discounting; at the same time, species able to reproduce clonally have ecological and evolutionary advantages being able to persist when conditions are not favorable for sexual reproduction. The presence of clonality has profound consequences on the genetic structure of populations, especially when it represents the predominant reproductive strategy in a population. Theoretical studies suggest that high rate of clonal propagation should increase the effective number of alleles and heterozygosity in a population, while an opposite effect is expected on genetic differentiation among populations and on genotypic diversity. In this study, we ask how clonal propagation affects the genetic diversity of rare insular species, which are often characterized by low levels of genetic diversity, hence at risk of extinction. We used eight polymorphic microsatellite markers to study the genetic structure of the critically endangered insular endemic Ruta microcarpa. We found that clonality appears to positively affect the genetic diversity of R. microcarpa by increasing allelic diversity, polymorphism, and heterozygosity. Moreover, clonal propagation seems to be a more successful reproductive strategy in small, isolated population subjected to environmental stress. Our results suggest that clonal propagation may benefit rare species. However, the advantage of clonal growth may be only short-lived for prolonged clonal growth could ultimately lead to monoclonal populations. Some degree of sexual reproduction may be needed in a predominantly clonal species to ensure long-term viability.

Longevity of clonal plants: why it matters and how to measure it

BACKGROUND

Species' life-history and population dynamics are strongly shaped by the longevity of individuals, but life span is one of the least accessible demographic traits, particularly in clonal plants. Continuous vegetative reproduction of genets enables persistence despite low or no sexual reproduction, affecting genet turnover rates and population stability. Therefore, the longevity of clonal plants is of considerable biological interest, but remains relatively poorly known.

SCOPE

Here, we critically review the present knowledge on the longevity of clonal plants and discuss its importance for population persistence. Direct life-span measurements such as growth-ring analysis in woody plants are relatively easy to take, although, for many clonal plants, these methods are not adequate due to the variable growth pattern of ramets and difficult genet identification. Recently, indirect methods have been introduced in which genet size and annual shoot increments are used to estimate genet age. These methods, often based on molecular techniques, allow the investigation of genet size and age structure of whole populations, a crucial issue for understanding their viability and persistence. However, indirect estimates of clonal longevity are impeded because the process of ageing in clonal plants is still poorly understood and because their size and age are not always well correlated. Alternative estimators for genet life span such as somatic mutations have recently been suggested.

CONCLUSIONS

Empirical knowledge on the longevity of clonal species has increased considerably in the last few years. Maximum age estimates are an indicator of population persistence, but are not sufficient to evaluate turnover rates and the ability of long-lived clonal plants to enhance community stability and ecosystem resilience. In order to understand the dynamics of populations it will be necessary to measure genet size and age structure, not only life spans of single individuals, and to use such data for modelling of genet dynamics.

Phylogenetic relationships and natural hybridization among the North American woody bamboos (Poaceae: Bambusoideae: Arundinaria)

In spite of the ecological and economic importance of temperate bamboos, relatively little is known about their population biology or evolutionary history. Recently, hybridization has emerged as a potential source of diversity in this group, as well as an underlying cause of taxonomic problems. As part of a broader phylogenetic study of the temperate bamboos, we report the results of an analysis of the North American Arundinaria gigantea species complex, including estimates of genetic variation and molecular evidence of natural hybridization among A. gigantea, A. tecta, and A. appalachiana. The study involved a comparative analysis of amplified fragment length polymorphisms (AFLPs) and chloroplast DNA sequences representing diversity within and among all three species plus individuals with intermediate or unusual morphological characteristics (putative hybrids). Molecular results support the recognition of three species previously defined on the basis of morphology, anatomy, and ecology, with most of the molecular variance accounted for by among-species variation. Molecular evidence also demonstrates that A. tecta and A. appalachiana are sister species, forming a clade that is significantly divergent from A. gigantea. The role of hybridization in the phylogenetic history of Arundinaria is discussed along with implications for the evolution and taxonomy of the temperate woody bamboos.

Hanging by a coastal strand: breeding system of a federally endangered morning-glory of the south-eastern Florida coast, Jacquemontia reclinata

BACKGROUND AND AIMS

Coastal development has led to extensive habitat destruction and the near extinction of the beach clustervine, Jacquemontia reclinata (Convolvulaceae), an endangered, perennial vine endemic to dune and coastal strand communities in south-eastern Florida. We examined the breeding system of this rare species, and observed visitors to its flowers, as part of a larger effort to document its status and facilitate its recovery.

METHODS

Reproductively mature experimental plants were grown from seed collected from wild plants in two of the largest remaining populations. Controlled hand pollinations on potted plants were conducted to determine the level of compatibility of the species and to investigate compatibility within and between populations. Seeds from the hand pollinations were planted in soil, and they were monitored individually, recording time to seed germination (cotyledon emergence). Wild plants were observed in several of the remaining populations to determine which species visited the flowers.

KEY RESULTS

Hand pollination and seed planting experiments indicate that J. reclinata has a mixed mating system: flowers are able to set fruit with viable seeds with self-pollen, but outcross pollen produces significantly greater fruit and seed set than self-pollen (> or =50 % for crosses vs. <25 % for self-pollinations). Visitors included a wide array of insect species, primarily of the orders Diptera, Hymenoptera and Lepidoptera. All visitors captured and examined carried J. reclinata pollen, and usually several other types of pollen.

CONCLUSIONS

Remnant populations of beach clustervine will have greater reproductive success not only if floral visitor populations are maintained, but also if movement of either pollen or seed takes place between populations. Restoration efforts should include provisions for the establishment and maintenance of pollinator populations.

Reproductive success of non-rewarding Cypripedium japonicum benefits from low spatial dispersion pattern and asynchronous flowering

BACKGROUND AND AIMS

Outcrossing animal-pollinated plants, particularly non-rewarding species, often experience pollinator limitation to reproduction. Pollinator visitation is affected by various factors, and it is hypothesized that reproduction in non-rewarding plants would benefit from low spatial flower abundance and asynchronous flowering. In order to test this hypothesis, the influence of spatial pattern and flowering phenology on male and female reproductive success (RS) was investigated in a non-rewarding orchid, Cypripedium japonicum, in central China over two flowering seasons.

METHODS

The probabilities of intrafloral self-pollination and geitonogamy caused by pollinator behaviours were estimated from field observations. Pollinator limitation was evaluated by hand-pollination experiments. RS was surveyed in different spatial flower dispersal patterns and local flower densities. The effects of flowering phenological traits on RS were assessed by univariate and multivariate regression analyses.

KEY RESULTS

Hand-pollination experiments revealed that fruit production was strongly pollen limited throughout the entire reproductive season - over two seasons, 74.3 % of individuals set fruit following hand pollination, but only 5.2-7.7 % did so under natural conditions. Intrafloral self-pollination and geitonogamy within the potential clones might be rare. Both male and female fitness were substantially lower in clustered plants than in those growing singly. An increase in local conspecific flower density significantly and negatively influenced male RS, but had no effect on female RS. Phenotypic selection analysis indicated that individuals flowering earlier have the greatest probability of RS. Over 85 % of sampled flowering individuals had a flowering synchrony value >0.7; however, highly synchronous flowering was not advantageous for RS, as indicated by the negative directional selection differentials and gradients, and by the positive quadratic selection gradients.

CONCLUSIONS

These results support the hypothesis that, as a consequence of density-dependent selection, low spatio-temporal flower abundance is advantageous for attracting pollinators and for reproduction in natural populations of non-rewarding C. japonicum.

Extensive clonality of the endemic Calamagrostis pseudopurpurea Gerstl. ex O.R. Heine in central Germany revealed by RAPD markers

Calamagrostis pseudopurpurea is one of only a few endemic species in Germany and is confined to the catchment area of the River Mulde in the states of Saxony and Saxony-Anhalt. We studied the genetic structure and seed viability across its entire distribution area. Patterns of random amplified polymorphic DNA (RAPD) variation were analysed using 183 individuals from 43 stands in order to assess the overall genetic structure and the extent of clonality. In addition, four related Calamagrostis species (C. canescens, C. epigejos, C. phragmitoides and C. villosa) were included in our study to consider the probable phylogenetic origin of C. pseudopurpurea. We detected two clearly different RAPD phenotypes of C. pseudopurpurea, each distributed along the river banks of two spatially isolated stream courses. Both phenotypes are present downstream of the confluence. Our results indicate that C. pseudopurpurea originates from two distinct periods of hybridisation between the same parental taxa, and that clonal propagation is most likely the main reproduction method. In line with its hybrid origin, embryos of sampled C. pseudopurpurea caryopses were found to be mostly degraded or unviable over several years. Calamagrostis pseudopurpurea is genetically closer to C. canescens and C. phragmitoides than it is to other studied species, but C. canescens and C. phragmitoides have not been proven to be direct parental taxa of C. pseudopurpurea. Calamagrostis pseudopurpurea should therefore still be treated as a separate species that needs special attention from a conservation point of view.

Comparison of clonal diversity in mountain and Piedmont populations of Trillium cuneatum (Melanthiaceae-Trilliaceae), a forest understory species

The balance between clonal and sexual reproduction can vary widely among plant populations, and the extent of clonality may be influenced by the combined effects of historical land use and variation in environmental conditions. We investigated patterns of clonal spread in five Trillium cuneatum populations, two in the Appalachian Mountains characterized by mesic, cooler conditions, and three at lower elevations experiencing warmer, drier conditions and greater disturbance. Using a new measure of the genet effective number and innovative orthogonal contrast methods, we quantified genet structure, contrasting clonal growth in the mountains with that in the Piedmont. Asexual propagation was more common in the Piedmont, where 25% of the sampled ramets were clonally derived, but was much less frequent in the mountains (7% clonal replicates). Hierarchical partitioning of variation in genet diversity showed that the majority (75.8%) of the variation resulted from more vegetative replication in the Piedmont. Most of the remaining variation (21.6%) was attributable to differences between urban and rural Piedmont populations, and a small, statistically nonsignificant fraction of the variation (2.6%) was due to interpopulation differences within the mountains. Higher frequency of cloning may enhance both genetic and demographic population viability in fragmented Piedmont habitats.

‘Sax-sess’- genetics of primary succession in a pioneer species on two parallel glacier forelands

The primary succession on glacier forelands is characterized by a sequence of early and late successional species, but whether there is also a chronosequence at the intraspecific, genetic level is a matter of debate. Two opposing hypotheses differ in their prediction of genetic diversity in colonizing populations due to founder effects and postcolonization gene immigration. The development of genetic diversity in the pioneer Saxifraga aizoides was investigated along a successional gradient on two parallel glacier forelands, in order to test whether populations from older successional stages were less genetically diverse than populations from younger successional stages, and to locate the sources of the propagules that originally colonized new glacier foreland. Genetic diversity was determined with amplified fragment length polymorphisms, and potential sources of colonizing propagules were assessed via assignment tests. Our results indicate considerable postcolonization gene flow among populations on glacier forelands, since population differentiation was low and genetic diversity within populations was significantly higher. Molecular diversity and differentiation of populations did not develop linearly. Dispersal events within the glacier foreland, from the adjacent valley slopes, and from parallel glacier valleys were identified. In summary, it seems that the colonization of glacier forelands in the European Alps is highly dynamic and stochastic.

Variation at a chloroplast minisatellite locus reveals the signature of habitat fragmentation and genetic bottlenecks in the rare orchid Anacamptis palustris (Orchidaceae)

Geoclimatic changes during the Oligocene and more recent anthropogenic influences have shaped the current distribution and population structure of Mediterranean plant species. Anacamptis palustris (Orchidaceae) is a typical member of coastal wetlands, which have become increasingly fragmented and isolated. As a consequence, this orchid has become rare in the recent past. Length variation at a chloroplast minisatellite locus was used to estimate genetic variation within and between the largest extant populations of A. palustris. Genetic diversity was positively correlated with population size. Estimation of observed and expected gene diversity and analyses of haplotype number and haplotype frequency distributions provided evidence for population bottlenecks in the history of small populations. Comparison with an earlier study suggests that nuclear allozyme diversity was most likely lost during the Oligocene and could not recover subsequently due to low mutation rates, whereas genetic variation was restored at the highly variable chloroplast minisatellite locus. Population bottlenecks indicated by cpDNA variation occurred most likely as a consequence of more recent anthropogenic changes. The comparison of molecular markers with different levels of polymorphism provided valuable insights into the processes shaping genetic diversity and population structure in this rare orchid.