Spatial genetic structure of two sympatric neotropical palms with contrasting life histories

The spatial genetic structure within sympatric populations of two neotropical dioecious palm species with contrasting life histories was characterized to evaluate the influence of life history traits on the extent of genetic isolation by distance. Chamaedorea tepejilote is a common wind-pollinated arboreal understory palm. Chamaedorea elatior is an uncommon climbing subcanopy palm with entomophilous pollination syndrome. A total of 59 allozyme alleles for C. tepejilote and 53 alleles for C. elatior was analyzed using both unweighted (Iu) and weighted (Iw) Moran's I spatial autocorrelation statistics. The spatial genetic structure detected within these populations is consistent with those reported for highly dispersed plants. A significance test for differences between mean Moran's I-coefficients revealed less spatial genetic structure within the C. tepejilote population than that in the C. elatior population. Adjacent individuals of C. elatior exhibited significant spatial genetic autocorrelation (Iu=0.039, Iw=0.034), indicating a Wright's neighborhood size of about 100 individuals. For C. tepejilote, nonrandom genetic distribution among nearest neighbors was detected, even from small spatial autocorrelation values (Iu=0.008, Iw=0.009), consistent with a neighborhood size of about 300 individuals. For both species, seed dispersal, mortality among life cycle stages, overlapping generations, and contrasting traits of mating and reproduction influence the standing spatial genetic structure within populations.     

Taxonomy and conservation: A case study from Chamaedorea alternans

BACKGROUND AND AIMS: The establishment of justified recommendations in conservation biology requires robust taxonomic treatments for the group(s) being considered. Controversial or poorly developed taxonomies can have a negative impact on conservation assessments. One example of a taxonomically difficult and controversial species complex that is important in conservation involves two species of Mexican palms, Chamaedorea tepejilote and C. alternans. The goal of this study was to investigate whether C. alternans and C. tepejilote are genetically distinct within the Los Tuxtlas region of Veracruz. METHODS: Individuals corresponding to the morphology of C. alternans and C. tepejilote were collected from sympatric and allopatric regions within the Los Tuxtlas Biological Station. Eighty-eight samples were genotyped using amplified fragment length polymorphism (AFLP) markers. Cluster and ordination analyses were used to investigate patterns of differentiation. KEY RESULTS: UPGMA and PCO analyses of AFLP profiles recovered two divergent clusters corresponding to morphologically defined C. tepejilote and C. alternans. No intermediate genotypes were observed and five of the 45 loci were fixed for either the presence or absence between the species. The patterns of divergence observed do not identify a role for sympatric speciation. CONCLUSIONS: The observed patterns of differentiation support the recognition of C. alternans as distinct from C. tepejilote. A suite of vegetative and reproductive morphological features can be used to help distinguish these taxa in the field, but they can be difficult to differentiate from preserved material. Previous treatments of the variation found within the complex (C. alternans and C. tepejilote) as intraspecific variance is unjustified. Given that the Los Tuxtlas region has suffered from historical and ongoing deforestation and that Chamaedorea includes numerous endangered taxa, retaining conservation status for C. alternans serves to help safeguard individuals of the species as well as a region and larger taxonomic group all under considerable threat from human activities.     

Biomass Allocation in the Dioecious Tropical Palm Chamaedorea tepejilote and Its Life History Consequences

Abstract The patterns of resource allocation are described for a dioecious tropical palm, Chamaedorea tepejilote. Resource allocation was measured by harvesting fifteen plants of C. tepejilote. The relative allocation of biomass in the stem increased with the size of the plant; that in the leaves decreased and that in the other structures remained roughly constant. Female plants showed a greater total reproductive effort, though male plants produced more inflorescences during the flowering season. Both male and female plants allocated more resources to prop root than to hypogeal roots. The annual productivity of reproductive and vegetative parts of C. tepejilote was estimated using allometric relationships for different plant structures and from demographic data obtained from the field. Annually, female plants allocated significantly more resources to leaves than male plants. Yearly productivity of inflorescences was higher for male plants, while female plants had greater total reproductive productivity (inflorescences and fruits). Correlation analysis showed an increase in reproductive effort with plant size, and an inverse relationship between fecundity and probability of survival, fecundity and residual reproductive value, and reproductive effort and life expectancy; these relationships suggested a cost in reproduction. Additionally, mature plants with different growth rates exhibited differences in fecundity: tall plants (>2.5m height) that grew more than 40 cm in height in four years had lower values of fecundity in comparison to plants of slower growth. These data were discussed in the context of the implications in the life history of a dioecious tropical plant.     

Morphological and genetic variation in seven species of the endangered Chirostoma "humboldtianum species group" (Atheriniformes: Atherinopsidae)

The Chirostoma "humboldtianum" group includes seven silverside species considered as a monophyletic assemblage because of their high genetic and morphological similarities. The group includes five moderately large species, "peces blancos" (117-300 mm standard length--SL) and two smaller species, "charales" (70-142 mm SL). These species are of great economical, cultural and ichthyological interest for local populations, and their management practices are controversial. We investigated the morphometric, meristic and allozyme variations of the seven species (13 populations) and related the variations with life history, habitat and management procedures. Nineteen morphometric variables, eight meristic variables (by multivariate analysis) and 23 allozyme loci of the seven species and populations of Chirostoma were compared. Principal component analysis (PC) of morphometric and meristic data indicate that both sets of data provided information to differentiate among the seven species. The variables that accounted for most of this differentiation were head length (HL), predorsal 1 length (PIL) and length of pelvic fin base (PfbL). PC and Discriminant Analysis (DA) with morphometric data also suggested the differentiation of populations within C. grandocule (83% correctly classified organisms), whereas PC and DA with meristic data differentiated populations of C. humboldtianum (80% correctly classified organisms). The most important morphometric variables for the differentiation were anal fin height (AfH), length of anal fin base (AfbL) and predorsal 2 length (P2L) and the meristic variables D2fR. PdS and AfR. The genetic variability data indicate changes in values of some of the species in relation to previously reported data. The present populations of C. grandocule show a reduction in He (0.002 vs. 0.009). Other species showed an increase; for instance, C. consocium consocium, C. humboldtianum, C. lucius, C. promelas and C. sphyraena averaged He = 0.069 vs 0.027. theta indicated significant genetic differentiation among the analysed species (0.247, S.D. 0.159) and theta s supported the morphological data that suggest intra-specific differentiation (0.360, S. D. 0.154).     

Genetic effects of habitat fragmentation in Viola pubescens (Violaceae), a perennial herb with chasmogamous and cleistogamous flowers

The reproductive biology of a plant species is important in the response of populations to habitat fragmentation, especially if plant-pollinator interactions are disrupted. The genetic effects of forest fragmentation were examined in the common understorey herb Viola pubescens, a species that produces self-pollinated cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers. Using allozymes, we measured genetic variation in different sized populations. These were located in woodlots of various sizes (0.5-40.5 ha) and distances from one another (0.3-46 km) within the agricultural landscape of central Ohio in the Midwestern United States. Changes in forest cover of each woodlot within the past 180 years were determined from historical sources and aerial photographs. Woodlot and population sizes were significantly and positively correlated with measures of genetic variation (A, P, HO and HE), with variation highest in populations in the largest woodlot population and lowest in the smallest woodlot population. Most large woodlots resulted from fluctuations in forest cover over the past 60 years, while smaller fragments remained the same size. Overall, populations in Crawford County were genetically differentiated from one another (theta = 0.34), but there was no relationship between genetic and geographical distance. Preliminary evidence for a single year indicated a high rate of outcrossing in most populations. Despite the CH/CL reproductive advantage and apparent outcrossing, populations of V. pubescens in small woodlots remain susceptible to potentially detrimental effects of fragmentation such as genetic drift and reduced levels of genetic variation.     

PERMANENT GENETIC RESOURCES: Development of microsatellite markers of the Mexican understorey palm Chamaedorea elegans, cross-species genotyping, and amplification in congeners

With striking morphological diversity and adaptability, Chamaedorea palms constitute an ecologically and economically important understorey component of Neotropical forests. Nine loci developed for Chamaedorea elegans evaluated in three Veracruz populations resulted in a large number of alleles (8-18), and high expected heterozygosity (0.49-0.92), but low observed (0.27-0.65) heterozygosity. Deviations from Hardy-Weinberg and high inbreeding suggest a lack of panmixia. Eight loci optimized for Chamaedorea ernesti-augustii showed similar patterns of variation. All nine multiplexing loci amplified in other five congeneric species, which will facilitate comparisons within the genus and contribute to the conservation of its genetic resources.     

Leaf production,reproductive patterns,field germination and seedling survival in Chamaedorea bartlingiana,a dioecious understory palm

Summary Chamaedorea bartlingiana is a dioecious palm that grows in the cloud forest understories of the Venezuelan Andes. Age and sexual differences in phenology and reproductive patterns were studied in labelled individuals of all age categories. This species has long-lived leaves and low leaf production, both characteristic of understory plants. Growth rates are lower in juveniles than in adults and in females than in males, as in other palms. Male and female individuals show different reproductive patterns. Male inflorescences are always produced at the same rate and the probability of surviving until anthesis is constant. Females produce reproductive buds at the same rate as males, but these buds have a 35% probability of becoming a ripe infrutescence if the plant has infrutescences already growing, and 70% if it does not. This pattern and the slow growth of inflorescences (1 year for males from bud to flowers, 2 years for females from bud to ripe fruits) cause a pluriannual reproductive pattern at the population level. Field germination does not follow this pattern, but shows one annual peak probably related to environmental conditions.     

Hierarchical components of genetic variation at a species boundary: population structure in two sympatric varieties of Lupinus microcarpus (Leguminosae)

Lupinus microcarpus is a self-compatible annual plant that forms a species complex of morphologically variable but indeterminate varieties. In order to examine the hypothesis that varieties of L. microcarpus comprise genetically differentiated and reproductively isolated species, populations of L. microcarpus var. horizontalis and var. densiflorus were sampled from an area of sympatry in central California and genotyped using six microsatellite loci. Bayesian clustering divided the total sample into two groups corresponding to the named varieties with extremely low levels of inferred coancestry. Similarly, maximum likelihood and distance methods for genetic assignment placed individuals in two nonoverlapping groups. Evidence for isolation by distance (IBD) within each variety was found at shorter distance classes, but varieties remained differentiated in sympatry. Furthermore, coalescent estimates of divergence time indicate separation within the past 950-5050 generations, with minimal gene flow after divergence. A four-level hierarchical analysis of molecular variance (amova) found significant levels of genetic differentiation among varieties (theta(P) = 0.292), populations within varieties (theta(S) = 0.449), subpopulations within populations (theta(SS) = 0.623), and individuals within subpopulations (f = 0.421); but the greatest degree of differentiation was at the subpopulation level. Although it is sometimes assumed that the magnitude of genetic differences (e.g. F(ST)) should be greater between species than among populations or subpopulations of the same species, shared ancestral polymorphism may lead to relatively low levels of differentiation at the species level, even as the stochastic effects of genetic drift generate higher levels of differentiation at lower hierarchical levels. These results suggest that L. microcarpus var. horizontalis and var. densiflorus are recently diverged yet reproductively isolated species, with high levels of inbreeding resulting from the combined effects of limited gene flow, demographic bottlenecks, and partial selfing in finite, geographically structured populations.     

Back from the brink: potential for genetic rescue in a critically endangered tree

Rare plant species are vulnerable to genetic erosion and inbreeding associated with small population size and isolation due to increasing habitat fragmentation. The degree to which these problems undermine population viability remains debated. We explore genetic and reproductive processes in the critically endangered long-lived tropical tree Medusagyne oppositifolia, an endemic to the Seychelles with a naturally patchy distribution. This species is failing to recruit in three of its four populations. We evaluate whether recruitment failure is linked to genetic problems associated with fragmentation, and if genetic rescue can mitigate such problems. Medusagyne oppositifolia comprises 90 extant trees in four populations, with only the largest (78 trees) having successful recruitment. Using 10 microsatellite loci, we demonstrated that genetic diversity is high (H(E) : 0.48-0.63; H(O) : 0.56-0.78) in three populations, with only the smallest population having relatively low diversity (H(E) : 0.26 and H(O) : 0.30). All populations have unique alleles, high genetic differentiation, and significant within population structure. Pollen and seed dispersal distances were mostly less than 100 m. Individuals in small populations were more related than individuals in the large population, thus inbreeding might explain recruitment failure in small populations. Indeed, inter-population pollination crosses from the large donor population to a small recipient population resulted in higher reproductive success relative to within-population crosses. Our study highlights the importance of maintaining gene flow between populations even in species that have naturally patchy distributions. We demonstrate the potential for genetic and ecological rescue to support conservation of plant species with limited gene flow.     

山西省榛属植物居群的SSR遗传多样性研究

利用9对SSR引物对山西省平榛(Corylus heterophylla Fisch)和毛榛(C.mandshurica Maxim.et Rupr.)野生居群、欧榛(C.avellana L.)和平欧杂种榛(C.heterophylla Fisch.×C.avellana L.)的人工栽培居群,共205个样本进行PCR扩增,共扩增出172个等位基因。每个位点的等位基因数为5~18个,平均等位基因数为12.5个。居群观测杂合度(Ho)和预期杂合度(He)的变化范围分别为0.395~0.665和0.778~0.906,表明榛属植物遗传多样性较高,其中平欧杂种榛的遗传多样性最高(He=0.867,I=2.271),毛榛遗传多样性最低(He=0.825,I=2.006)。不同物种居群间遗传分化系数FST=0.106,平均基因流Nm=2.609,表明居群间的遗传分化水平较低。各居群在大多数位点上偏离Hardy-Weinberg平衡,主要原因是人工选择或近交所致。分子方差分析(AMOVA)表明,遗传变异主要发生在物种居群内。NJ聚类结果显示毛榛和平榛多数个体聚在各自居群内,平欧杂种榛和欧榛个体交互混合组成一小支后再与平榛聚在一起,表明平欧杂种榛与欧榛、平榛的亲缘关系较近,而毛榛与其它3种榛属植物的亲缘关系较远。本研究还分析讨论了山西省榛属植物居群具有较高遗传多样性的原因,并提出了野生榛子的保护利用策略。     

Reproductive biology and genetic structure in Lloydia serotina

Concern regarding the conservation status of small, isolated populations of the arctic-alpine plant species Lloydia serotina prompted research to establish the status and performance of this species in Wales, in comparison with large populations in its more typical alpine habitat. Relationships between reproductive strategies and genetic variation were investigated in a number of populations, representing a wide habitat, geographic and population size range. In all populations, vegetative reproduction predominates over sexual reproduction, but seed produced is viable and germinates readily under controlled conditions. Smaller, peripheral populations produced fewer flowers and seeds than the larger ones, but all populations studied supported significant percentages (>30%) of male plants, due to either the occurrence of androdioecy in this species or to a resource limited breeding system. Analysis of allozyme variation in sixteen populations from North America, the European Alps and Wales showed lower levels of genetic variation in smaller populations which averaged 1.1–1.2 alleles per locus and 10–20% of loci polymorphic, whereas larger populations averaged 1.4 alleles per locus and 30–40% polymorphic loci. This applied especially to the most northerly and southerly populations in North America, suggesting the occurrence of genetic drift in these small, peripheral populations. F-statistics suggest relatively high levels of differentiation among smaller populations, even among those closely related geographically, but genetic variation has been retained in all but one population, possibly due to infrequent sexual reproduction by long lived clones. RAPD analysis of four small populations in Wales provided further evidence of clonal growth and possible inbreeding dominating a mixed mating reproductive system with consequent genetic structuring in these populations.     

High genetic diversity in the remnant island population of hihi and the genetic consequences of re-introduction

The maintenance of genetic diversity is thought to be fundamental for the conservation of threatened species. It is therefore important to understand how genetic diversity is affected by the re-introduction of threatened species. We use establishment history and genetic data from the remnant and re-introduced populations of a New Zealand endemic bird, the hihi Notiomystis cincta, to understand genetic diversity loss and quantify the genetic effects of re-introduction. Our data do not support any recent bottleneck events in the remnant population. Furthermore, all genetic diversity measures indicate the remnant hihi population has retained high levels of genetic diversity relative to other New Zealand avifauna with similar histories of decline. Genetic diversity (N(A) , alleles per locus, allelic richness, F(IS) and H(S) ) did not significantly decrease in new hihi populations founded through re-introduction when compared to their source populations, except in the Kapiti Island population (allelic richness and H(S) ) which had very slow post-re-introduction population growth. The N(e) /N(c) ratio in the remnant population was high, but decreased in first-level re-introductions, which together with significant genetic differentiation between populations (F(ST) & Fisher's exact tests) suggest that extant populations are diverging as a result of founder effects and drift. Importantly, simulations of future allele loss predict that the number of alleles lost will be higher in populations with a slow population growth, fewer founding individuals and with nonrandom mating. Interestingly, this species has very high levels of extra-pair paternity which may reduce reproductive variance by allowing social and floater males to reproduce a life history trait that together with a large remnant population size may help maintain higher levels of genetic diversity than expected.     

Genetic variation and reproductive system among North American species of Nuttallanthus (Plantaginaceae)

We examined the effect of reproductive and life history strategies on the amount and partitioning of genetic variation in three annual species of Nuttallanthus. The North American species N. canadensis, N. floridanus, and N. texanus have regional to widespread ranges that overlap in the southeastern USA, are characterized by homogeneous populations and high fecundity, and possess showy, fragrant flowers seemingly adapted for insect pollination and outbreeding. Field and greenhouse studies on plants from 25 populations indicated that reproductive strategies were similar among species and showed predominant self-fertilization via cleistogamy and self-pollination prior to anthesis in chasmogamous flowers. Species were reproductively isolated and demonstrated complete cross-incompatibility after experimental crosses and no evidence for hybridization in mixed populations. Genetic variation was assessed using starch gel electrophoresis to resolve 15 isozyme loci in 50 populations. Conspecific genetic identity (I) values were high (0.819-0.936), but interspecific comparisons indicated many qualitative allelic differences and correspondingly low I values (0.516-0.623). Low levels of polymorphism and observed heterozygosity within populations and the disproportionate amount of gene diversity distributed among populations were concordant with reproductive data. The pattern of genetic differentiation was most similar to that observed in species with a predominantly inbreeding mating system.     

Genetic diversity of an amphicarpic species, Amphicarpaea edgeworthii Benth. (Leguminosae) based on RAPD markers

Amphicarpaea edgeworthii Benth. is an amphicarpic legume widespread in China. Amphicarpy describes the phenomenon that a plant produces aerial as well as subterranean fruits. A. edgeworthii can reproduce via three kinds of flowers: aerial chasmogamous flowers, aerial cleistogamous flowers, and subterranean cleistogamous flowers. Although there are some studies on the population genetic structure of species with both chasmogamous and cleistogamous flowers, none has been done for that of an amphicarpic species so far. The present study uses random amplified polymorphic DNA (RAPD) to assess level and pattern of genetic variation in 15 natural populations of A. edgeworthii. A total of 131 stable and clearly scored RAPD bands were achieved from 13 primers. The average genetic diversity within populations estimated by Shannon's information index was 0.218 at the population level, but ranged from 0.119 to 0.302, which was significantly different (P < 0.01). Different statistical analyses revealed a high level of genetic differentiation among populations (G_ST = 0.473–0.527). Thus, the pattern of genetic structure of A. edgeworthii is consistent with that of an inbreeding species.     

Population genetic structure of the endangered tropical tree species Caryocar brasiliense, based on variability at microsatellite loci

We report the population genetic structure of the endangered tropical tree species Caryocar brasiliense, based on variability at 10 microsatellite loci. Additionally, we compare heterozygosity and inbreeding estimates for continuous and fragmented populations and discuss the consequences for conservation. For a total of 314 individuals over 10 populations, the number of alleles per locus ranged from 20 to 27 and expected and observed heterozygosity varied from 0.129 to 0.924 and 0.067 to 1.000, respectively. Significant values of theta and R(ST) showed important genetic differentiation among populations. theta was much lower than R(ST), suggesting that identity by state and identity by descent have diverged in these populations. Although a significant amount of inbreeding was found under the identity by descent model (f = 0.11), an estimate of inbreeding for microsatellite markers based on a more adequate stepwise mutation model showed no evidence of nonrandom mating (R(IS) = 0.04). Differentiation (pairwise F(ST)) was positively correlated with geographical distance, as expected under the isolation by distance model. No effect of fragmentation on heterozygosity or inbreeding could be detected. This is most likely due to the fact that Cerrado fragmentation is a relatively recent event (approximately 60 years) compared to the species life cycle. Also, the populations surveyed from both fragmented and disturbed areas were composed mainly of adult individuals, already present prior to ecosystem fragmentation. Adequate hypothesis testing of the effect of habitat fragmentation will require the recurrent analysis of juveniles across generations in both fragmented and nonfragmented areas.     

Study on Population Genetic Structure in Castanopsis fargesii with Microsatellite Markers

Genetic structure of four populations in Castanopsis fargesii Franch. in Fujian Province was studied with microsatellite (SSR) markers. A high level of genetic variation was detected in the populations of C. fargesii by using SSR with A=9.0, Ne=4.8, He=0.65 and the population differentiation coefficient ( Fst ) was only 0.031. The distributions of alleles of all loci were significantly different among the populations of C. fargesii , and the population differentiation could be found according to the distributions of SSR alleles. Some rare alleles in the populations of C. fargesii were revealed by SSR: Fifteen of 54 alleles appeared in one or two populations with lower frequencies; conservation of these rare alleles is of great importance.     

Population genetic structure of diploid sexual and polyploid apomictic hawthorns (Crataegus; Rosaceae) in the Pacific Northwest

Polyploidy and gametophytic apomixis are two important and associated processes in plants. Many hawthorn species are polyploids and can reproduce both sexually and apomictically. However, the population genetic structure of these species is poorly understood. Crataegus douglasii is represented exclusively by self-compatible tetraploid pseudogamous apomicts across North America, whereas Crataegus suksdorfii found in the Pacific Northwest is known to include self-incompatible diploid sexuals as well as polyploid apomicts. We compare population structure and genetic variability in these two closely related taxa using microsatellite and chloroplast sequence markers. Using 13 microsatellite loci located on four linkage groups, 251 alleles were detected in 239 individuals sampled from 15 localities. Within-population multilocus genotypic variation and molecular diversity are greatest in diploid sexuals and lowest in triploid apomicts. Apart from the isolation of eastern North American populations of C. douglasii , there is little evidence of isolation by distance in this taxon. Genetic diversity in western populations of C. douglasii suggests that gene flow is frequent, and that colonization and establishment are often successful. In contrast, local populations of C. suksdorfii are more markedly differentiated. Gene flow appears to be limited primarily by distance in diploids and by apomixis and self-compatibility in polyploids. We infer that apomixis and reproductive barriers between cytotypes are factors that reduce the frequency of gene flow among populations, and may ultimately lead to allopatric speciation in C. suksdorfii . Our findings shed light on evolution in woody plants that show heterogeneous ploidy levels and reproductive systems.     

Molecular evidence for selection on female color polymorphism in the damselfly Ischnura graellsii

The significance of female color polymorphism in Odonata remains controversial despite many field studies. The importance of random factors (founder effects, genetic drift and migration) versus selective forces for the maintenance of this polymorphism is still discussed. In this study, we specifically test whether the female color polymorphism of Ischnura graellsii (Odonata, Coenagrionidae) is under selection in the wild. We compared the degree of genetic differentiation based on RAPD markers (assumed to be neutral) with the degree of differentiation based on color alleles. Weir and Cockerham's theta values showed a significant degree of population differentiation for both sets of loci (RAPD and color alleles) but the estimated degree of population differentiation (theta) was significantly greater for the set of RAPD loci. This result shows that some sort of selection contributes to the maintenance of similar color morph frequencies across the studied populations. Our results combined with those of previous field studies suggest that at least in some I. graellsii populations, density-dependent mechanisms might help to prevent the loss of this polymorphism but cannot explain the similarity in morph frequencies among populations.     

Population genetic structure of mahogany (Swietenia macrophylla King, Meliaceae) across the Brazilian Amazon, based on variation at microsatellite loci: implications for conservation

Mahogany (Swietenia macrophylla, Meliaceae) is the most valuable and intensively exploited Neotropical tree. No information is available regarding the genetic structure of mahogany in South America, yet the region harbours most of the unlogged populations of this prized hardwood. Here we report on the genetic diversity within and the differentiation among seven natural populations separated by up to 2100 km along the southern arc of the Brazilian Amazon basin. We analysed the variation at eight microsatellite loci for 194 adult individuals. All loci were highly variable, with the number of alleles per locus ranging from 13 to 27 (mean = 18.4). High levels of genetic diversity were found for all populations at the eight loci (mean HE = 0.781, range 0.754-0.812). We found moderate but statistically significant genetic differentiation among populations considering both estimators of FST and RST, theta = 0.097 and rho = 0.147, respectively. Estimates of theta and rho were significantly greater than zero for all pairwise population comparisons. Pairwise rho-values were positively and significantly correlated with geographical distance under the isolation-by-distance model. Furthermore, four of the populations exhibited a significant inbreeding coefficient. The finding of local differentiation among Amazonian mahogany populations underscores the need for in situ conservation of multiple populations of S. macrophylla across its distribution in the Brazilian Amazon. In addition, the occurrence of microgeographical genetic differentiation at a local scale indicates the importance of maintaining populations in their diverse habitats, especially in areas with mosaics of topography and soil.     

Genetic structure among and within peripheral and central populations of three endangered floodplain violets

Understanding the partitioning of genetic variance in peripheral and central populations may shed more light on the effects of genetic drift and gene flow on population genetic structure and, thereby, improve attempts to conserve genetic diversity. We analysed genetic structure of peripheral and central populations of three insect-pollinated violets (Viola elatior, Viola pumila, Viola stagnina) to evaluate to what extent these patterns can be explained by gene flow and genetic drift. Amplified fragment length polymorphism was used to analyse 930 individuals of 50 populations. Consistent with theoretical predictions, peripheral populations were smaller and more isolated, differentiation was stronger, and genetic diversity and gene flow lower in peripheral populations of V. pumila and V. stagnina. In V. elatior, probably historic fragmentation effects linked to its specific habitat type were superimposed on the plant geographic (peripheral-central) patterns, resulting in lower relative importance of gene flow in central populations. Genetic variation between regions (3-6%), among (30-37%) and within populations (60-64%) was significant. Peripheral populations lacked markers that were rare and localized in central populations. Loss of widespread markers in peripheral V. stagnina populations indicated genetic erosion. Autocorrelation within populations was statistically significant up to a distance of 10-20 m. Higher average genetic similarity in peripheral populations than in central ones indicated higher local gene flow, probably owing to management practices. Peripheral populations contributed significantly to genetic variation and contained unique markers, which made them valuable for the conservation of genetic diversity.