Recovery process of genetic diversity through seed and pollen immigration at the northernmost leading-edge population of Fagus crenata

The range expansion of a plant species begins with colonization of ecological empty patches from posterior source populations. This process involves stochastic loss of genetic diversity. However, the founder population could restore genetic diversity by gene flow from posterior populations via seeds and pollen and its recovery affects evolutionary potential for species expansion. To clarify the recovery process of genetic diversity during species range expansion, gene flow via seeds and pollen was investigated at the expansion front of Fagus crenata. Based on eight nuclear microsatellite genotypes of a total of 150 individuals and 225 seeds at the northernmost leading-edge population, genetic diversity, fine-scale spatial genetic structure (FSGS), and genetic differentiation from other five northern populations were investigated. Moreover, both seed and pollen immigration and their effects on genetic diversity at different successional stages were analyzed. The leading-edge population showed lower genetic diversity and substantial genetic differentiation, reflecting its strong genetic drift. Non-significant FSGS and a negative inbreeding coefficient for mature trees may indicate that the earliest generation consisted of founders from foreign seed sources. The significant proportion of seed and pollen immigration increased the number of different alleles for later successional stages. The effective number of pollen parents from foreign sources (20.8) was markedly higher than that from the local source (2.1). These results indicated that pollen immigration incorporated new and rare alleles and increased the genetic diversity of the population. However, the proportion of foreign gene flow decreased during succession, probably due to the increased reproductive success of local individuals as they reached maturity and grew in size.     

A multiscale analysis of gene flow for the New England cottontail,an imperiled habitat specialist in a fragmented landscape

Landscape features of anthropogenic or natural origin can influence organisms' dispersal patterns and the connectivity of populations. Understanding these relationships is of broad interest in ecology and evolutionary biology and provides key insights for habitat conservation planning at the landscape scale. This knowledge is germane to restoration efforts for the New England cottontail (Sylvilagus transitionalis), an early successional habitat specialist of conservation concern. We evaluated local population structure and measures of genetic diversity of a geographically isolated population of cottontails in the northeastern United States. We also conducted a multiscale landscape genetic analysis, in which we assessed genetic discontinuities relative to the landscape and developed several resistance models to test hypotheses about landscape features that promote or inhibit cottontail dispersal within and across the local populations. Bayesian clustering identified four genetically distinct populations, with very little migration among them, and additional substructure within one of those populations. These populations had private alleles, low genetic diversity, critically low effective population sizes (3.2–36.7), and evidence of recent genetic bottlenecks. Major highways and a river were found to limit cottontail dispersal and to separate populations. The habitat along roadsides, railroad beds, and utility corridors, on the other hand, was found to facilitate cottontail movement among patches. The relative importance of dispersal barriers and facilitators on gene flow varied among populations in relation to landscape composition, demonstrating the complexity and context dependency of factors influencing gene flow and highlighting the importance of replication and scale in landscape genetic studies. Our findings provide information for the design of restoration landscapes for the New England cottontail and also highlight the dual influence of roads, as both barriers and facilitators of dispersal for an early successional habitat specialist in a fragmented landscape.     

MICROSATELLITE MARKERS REVEAL POPULATION GENETIC STRUCTURE OF THE TOXIC DINOFLAGELLATE ALEXANDRIUM TAMARENSE (DINOPHYCEAE) IN JAPANESE COASTAL WATERS1

This is the first report to explore the fine‐scale diversity, population genetic structure, and biogeography of a typical planktonic microbe in Japanese and Korean coastal waters and also to try to detect the impact of natural and human‐assisted dispersals on the genetic structure and gene flow in a toxic dinoflagellate species. Here we present the genetic analysis of Alexandrium tamarense (Lebour) Balech populations from 10 sites along the Japanese and Korean coasts. We used nine microsatellite loci, which varied widely in number of alleles and gene diversity across populations. The analysis revealed that Nei's genetic distance correlated significantly with geographic distance in pair‐wise comparisons, and that there was genetic differentiation in about half of 45 pair‐wise populations. These results clearly indicate genetic isolation among populations according to geographic distance and restricted gene flow via natural dispersal through tidal currents among the populations. On the other hand, high P‐values in Fisher's combined test were detected in five pair‐wise populations, suggesting similar genetic structure and a close genetic relationship between the populations. These findings suggest that the genetic structure of Japanese A. tamarense populations has been disturbed, possibly by human‐assisted dispersal, which has resulted in gene flow between geographically separated populations.     

Integrating gene flow, crop biology, and farm management in on-farm conservation of avocado (Persea americana, Lauraceae)

Maintaining crop diversity on farms where cultivars can evolve is a conservation goal, but few tools are available to assess the long-term maintenance of genetic diversity on farms. One important issue for on-farm conservation is gene flow from crops with a narrow genetic base into related populations that are genetically diverse. In a case study of avocado (Persea americana var. americana) in one of its centers of diversity (San Jerónimo, Costa Rica), we used 10 DNA microsatellite markers in a parentage analysis to estimate gene flow from commercialized varieties into a traditional crop population. Five commercialized genotypes comprised nearly 40% of orchard trees, but they contributed only about 14.5% of the gametes to the youngest cohort of trees. Although commercialized varieties and the diverse population were often planted on the same farm, planting patterns appeared to keep the two types of trees separated on small scales, possibly explaining the limited gene flow. In a simulation that combined gene flow estimates, crop biology, and graft tree management, loss of allelic diversity was less than 10% over 150 yr, and selection was effective in retaining desirable alleles in the diverse subpopulation. Simulations also showed that, in addition to gene flow, managing the genetic makeup and life history traits of the invasive commercialized varieties could have a significant impact on genetic diversity in the target population. The results support the feasibility of on-farm crop conservation, but simulations also showed that higher levels of gene flow could lead to severe losses of genetic diversity even if farmers continue to plant diverse varieties.     

Multi-scale genetic analysis of Uniola paniculata (Poaceae): a coastal species with a linear, fragmented distribution

Geographic and fine-scale population genetic structures of Uniola paniculata, the dominant coastal dune grass in the southeastern USA, were examined. The linear, naturally fragmented distribution of this native perennial was hypothesized to lead to high genetic structure and lower genetic diversity at the margin of the species range. The extensive ramet production and low seed germination of this species were also expected to cause populations to be dominated by a few large clones. At 20 sites throughout the range of the species, leaf tissue was collected from 48 individuals. Clonal structure was examined using leaf tissue collected from an additional 60 individuals, each in four patches at two sites. Starch gel electrophoresis was used to resolve 27 allozyme loci. The results indicated that Uniola had greater genetic structure (G(ST) = 0.304) than most other outcrossing species, indicating moderate barriers to gene flow. There was a weak but significant positive relationship between genetic distance and geographic distance, supporting an isolation-by-distance model of gene flow. There were no obvious disjunctions between regions. Genetic diversity (H(e)) was relatively uniform throughout most of the range of the species but was lower in all western Gulf of Mexico populations. Clonal diversity varied both within and among sites, but clones were often small, suggesting that sexual reproduction and recruitment from seeds are important factors maintaining genetic diversity.     

Effects of flowering tree density on the mating system and gene flow in Shorea leprosula (Dipterocarpaceae) in Peninsular Malaysia

Pristine tropical rainforests in Southeast Asia have rich species diversity and are important habitats for many plant species. However, the extent of these forests has declined in recent decades and they have become fragmented due to human activities. These developments may reduce the genetic diversity of species within them and, consequently, the species’ ability to adapt to environmental changes. Our objective in the study presented here was to clarify the effect of tree density on the genetic diversity and gene flow patterns of Shorea leprosula Miq. populations in Peninsular Malaysia. For this purpose, we related genetic diversity and pollen flow parameters of seedling populations in study plots to the density of mature trees in their vicinity. The results show that gene diversity and allelic richness were not significantly correlated to the mature tree density. However, the number of rare alleles among the seedlings and the selfing rates of the mother trees were negatively correlated with the density of the adult trees. Furthermore, in a population with high mature tree density pollination distances were frequently <200 m, but in populations with low adult tree density the distances were longer. These findings suggest that the density of flowering trees affects selfing rates, gene flow and, thus, the genetic diversity of S. leprosula populations. We also found an individual S. leprosula tree with a unique reproductive system, probably apomictic, mating system.     

利用SSR分子标记分析秦岭冷杉自然居群的遗传多样性

利用10对SSR引物对濒危植物秦岭冷杉(Abies chensiensis)6个自然居群的120个个体进行了遗传多样性研究,旨在分析秦岭冷杉6个自然居群的遗传多样性、遗传结构及基因流变化.研究结果表明,120个个体在10个位点上共检测到149个等位基因,平均每个位点的等位基因数(A)为14.9,每个位点的有效等位基因数(e)为7.7,每个位点的平均预期杂合度(He)和平均观察杂合度(Ho)分别为0.841和0.243,Shannon多样性指数(Ⅰ)为2.13,自然居群杂合性基因多样度的比率(FsT)为6.7％,居群间的基因流(Nm)为3.45.利用Mantel检测到自然居群的遗传距离与地理距离间无显著相关性(r=0.490 6,P＞0.05).秦岭冷杉自然居群的遗传多样性水平较低,遗传变异主要存在于居群内部.结合研究数据、实地调查及相关资料,推测秦岭冷杉自然居群间基因流较原来增大可能是因为居群间发生了远交衰退.     

Cross-amplification of microsatellite loci in a neotropicalQuercus species and standardization of DNA extraction from mature leaves dried in silica gel

Conservation of 15 out of 24 previously identified microsatellite loci (62.5%), was found in a survey of the South American oak,Quercus humboldtii. The number of alleles per locus varied from 2 to 20, detecting at least 5 microsatellite loci with 5 or more alleles. This number of loci and alleles is adequate for most studies of genetic diversity and gene flow analysis. In addition, a method for extracting DNA from mature oak leaves is described that minimizes oxidation of tannins, a common problem in silica-gel-dried samples. The microsatellite markers detected in this study and the DNA extraction protocol may be applied to more than 30 species ofQuercus that exist in tropical America.     

Genetic variation and population structure in Korean populations of eurya japonica (Theaceae)

We investigated levels of genetic diversity, population genetic structure, and gene flow in Eurya japonica, a widespread and broad-leaved evergreen dioecious tree native to Japan, China, Taiwan, and the southern and southwestern coast of the Korean Peninsula. Starch-gel electrophoresis was conducted on leaves collected from 1,000 plants in 20 Korean populations. All 12 loci examined were polymorphic in at least one population, and the mean number of alleles per locus was 3.79. In addition, mean observed population heterozygosity (Ho_p = 0.425), expected heterozygosity (He_p = 0.462), and total genetic diversity (H_T = 0.496) were substantially higher than average values for species with similar life history traits. Although significant differences in allele frequency were detected between populations at all loci (P < 0.001), <7% of the genetic variation was found among populations (F_ST = 0.069). There was a significant negative correlation between genetic identity and distance between populations (r = -0.341; P < 0.05), but this explained only a small amount of the diversity among populations. Indirect estimates of the number of migrants per generation (Nm) (3.37, calculated from F_ST; 3.74, calculated from the mean frequency of eight private alleles) indicate that gene flow is extensive among Korean populations of E. japonica. Factors contributing to the high levels of genetic diversity found within populations of E. japonica include large and contiguous populations, obligating outcrossing (dioecious plant), high fecundity, and long generation time. Occasional seed dispersal by humans and pollen movement by domesticated honey bees may further enhance gene flow within the species.     

Population structure, genetic diversity, and clone formation in Quercus chrysolepis (Fagaceae)

Stands of canyon live oak (Quercus chrysolepis, Fagaceae) are maintained for fuelwood, fire management, recreation, and as habitat for wildlife. Information about the link between the oak's reproductive ecology and its extent of genetic diversity is important in developing land management policies that will maintain the long-term viability of populations. Basal sprouting is the primary means of reproduction following fire or cutting, and stands frequently include groups of visibly connected trees in a clustered distribution that suggests cloning. We determined the extent to which clusters of trees were clonal and defined the spatial pattern and diversity of genotypes for six populations across nearly the entire east-west extent of the San Bernardino Mountains in southern California. We mapped over 100 trees at each of five sites and genotyped each tree for allozymes at seven polymorphic loci. We identified clones using these multilocus genotypes and detected an average of 34.4 ± 7.3 (SD) clones per site, most of which had unique genotypes. In general, clustered trees belong to single clones and most clones consist of few trees (mean = 3.4 ± 0.6 trees per clone). However, clone size increased significantly with increased individual heterozygosity, suggesting that selection may favor highly heterozygous clones. Clonal diversity and evenness were high relative to reports for most other clonal species; an average of 97% of clones had distinct genotypes, and Simpson's index of diversity averaged 0.95 ± 0.02. Population genetic analyses of 319 clones from six sites revealed high genetic diversity within sites (mean HS = 0.443). Only a small proportion of the total genetic diversity was explained by variation among sites (mean GST = 0.018), which is consistent with high gene flow among sites (Nm = 9.5). We found no significant substructure among plots within sites, and fixation indices within sites were generally small, suggesting that either little inbreeding occurs, and/or few inbred progeny survive. However, spatial autocorrelation analysis of clones indicated fine-scale genetic structure at distances under 4 m, possibly due to limited seed dispersal. Our data suggest that guidelines for seed collection of canyon live oak for use in restoration can be specified in a manner similar to that recommended for conifer species within the region studied.     

鄂尔多斯高原不同降雨量梯度中间锦鸡儿(Caragana davazamcii Sancz)种群的遗传结构

为了阐明环境条件对中间锦鸡儿适应状况的影响,在鄂尔多斯高原从东向西按照降雨逐渐减少的梯度选取了5个生境,从遗传多样性的角度出发,应用简单重复间序列（ISSR）方法,对各生境的中间锦鸡儿种群进行了分子生态学研究．结果表明随着生境由东向西的变化,多年平均降雨量的减少,中间锦鸡儿种群遗传多样性有所增加,大部分变异发生在种群内（79．95％）,属异交类型,中间锦鸡儿群体间遗传距离缓慢增加,遗传一致度降低,说明生境条件的变化特别是长期形成的水分条件对中间锦鸡儿的遗传多样性有一定的影响。     

Genetic variation within and between populations of hermaphroditic <Emphasis Type="Italic">Bulinus truncatus</Emphasis> tetraploid freshwater snails of the Albertine Rift,East Africa

Genetic variability within and among Bulinus truncatus of the Albertine Rift freshwater bodies were assessed to investigate the degree of inbreeding and gene flow in the snail populations. The effect of ploidy on the genetic structuring of B. truncatus is also described. We characterized the genetic structure of seven B. truncatus populations from Lake Albert, Lake Kivu, and Katosho swamp in Tanzania using five polymorphic microsatellite loci. Genetic differentiation was quantified using pairwise FST values and Nei’s standard genetic distances. Different alleles were observed across all loci and genetic diversity was low although it varied greatly across populations; observed heterozygosity was, however, higher than the expected heterozygosity in three of the populations studied. Significant heterozygote deficiencies were observed coupled with significant linkage disequilibria in five populations for all the five loci examined in this study. We found significant genetic differentiation among the seven freshwater bodies; private alleles were observed across all loci indicating restricted or absence of gene flow between populations. Limited snail dispersal and the reproductive biology of B. truncatus are the major forces shaping the genetic variation observed. Low genetic variation within B. truncatus populations exposes them to a high parasite infection risk as predicted in the Red Queen hypothesis.     

Genetic structure and relationships within and between cultivated and wild sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench) in Kenya as revealed by microsatellite markers

Understanding the extent and partitioning of diversity within and among crop landraces and their wild/weedy relatives constitutes the first step in conserving and unlocking their genetic potential. This study aimed to characterize the genetic structure and relationships within and between cultivated and wild sorghum at country scale in Kenya, and to elucidate some of the underlying evolutionary mechanisms. We analyzed at total of 439 individuals comprising 329 cultivated and 110 wild sorghums using 24 microsatellite markers. We observed a total of 295 alleles across all loci and individuals, with 257 different alleles being detected in the cultivated sorghum gene pool and 238 alleles in the wild sorghum gene pool. We found that the wild sorghum gene pool harbored significantly more genetic diversity than its domesticated counterpart, a reflection that domestication of sorghum was accompanied by a genetic bottleneck. Overall, our study found close genetic proximity between cultivated sorghum and its wild progenitor, with the extent of crop-wild divergence varying among cultivation regions. The observed genetic proximity may have arisen primarily due to historical and/or contemporary gene flow between the two congeners, with differences in farmers’ practices explaining inter-regional gene flow differences. This suggests that deployment of transgenic sorghum in Kenya may lead to escape of transgenes into wild-weedy sorghum relatives. In both cultivated and wild sorghum, genetic diversity was found to be structured more along geographical level than agro-climatic level. This indicated that gene flow and genetic drift contributed to shaping the contemporary genetic structure in the two congeners. Spatial autocorrelation analysis revealed a strong spatial genetic structure in both cultivated and wild sorghums at the country scale, which could be explained by medium- to long-distance seed movement.     

基于微卫星标记的中国枣食芽象甲地理种群遗传多样性分析

【目的】枣食芽象甲Scythropus yasumatsui是我国北方枣树Zizyphus jujuba上的一种重要的灾害性害虫,在陕西、山西、河北、河南等枣树主产区普遍发生。本研究旨在揭示我国枣食芽象甲不同种群间的遗传分化和基因交流规律。【方法】利用枣食芽象甲转录组测序的SSR序列,使用荧光标记PCR及毛细管电泳分型方法,筛选出8个微卫星位点,对我国5个省份(山西、陕西、宁夏、河北和河南)10个地理种群共308头枣食芽象甲样本进行种群遗传多样性分析。【结果】8个SSR位点均存在无效等位基因且偏离哈迪 温伯格平衡。各位点的有效等位基因数(Ne)为2.113~8.016,多态信息含量(PIC)为0.561~0.908,期望杂合度(He)为0.476~0.865;种群间遗传分化系数(Fst)平均值为0.151;基因流(Nm)平均值为1.594。枣食芽象甲种群间遗传分化系数与地理距离之间显著正相关(r=0.596, P=0.0035),基于Nei’s遗传距离和Cavalli-Sforza & Edwards余弦遗传距离的系统进化树将10个地理种群均聚为3个相同的分支。【结论】结果说明,枣食芽象甲种群遗传多样性较高,不同地理种群间存在高度的遗传分化,且有一定的基因交流;地理隔离是影响枣食芽象甲地理种群遗传分化和基因交流的重要因素。     

Conservation of the Lake Kasumigaura population of Nymphoides indica (L.) Kuntze based on genetic evaluation using microsatellite markers

We compared the genetic diversity of the Lake Kasumigaura population of Nymphoides indica with that of pond populations in Hyogo and Kagawa Prefectures, which are thought to maintain high genetic diversity, to elucidate the current genetic diversity and occurrence of distinctive alleles in the Lake Kasumigaura population. The genetic diversity, as measured by the mean number of alleles per polymorphic locus, effective number of alleles per locus, mean observed heterozygosity, mean expected heterozygosities, total gene diversity, and number of multilocus genotypes was lower in the Lake Kasumigaura population than in the Hyogo and Kagawa populations. In addition, the inbreeding coefficient suggests that random mating does not occur in the Lake Kasumigaura population. The degree of genetic differentiation between the Lake Kasumigaura population and the Hyogo and Kagawa populations suggests that the Lake Kasumigaura population is largely genetically distinct. We found five genotypes in the Lake Kasumigaura population that were absent from the Hyogo and Kagawa populations. These results demonstrate that the Lake Kasumigaura population is an important component of the overall genetic diversity of N. indica in Japan.     

Biotic and abiotic factors affecting the genetic structure and diversity of butternut in the southern Appalachian Mountains,USA

The abundance of butternut (Juglans cinerea L.) trees has severely declined rangewide over the past 50 years. An important factor in the decline is butternut canker, a disease caused by the fungus Ophiognomonia clavigigenti-juglandacearum, which has left the remaining butternuts isolated and sparsely distributed. To manage the remaining populations effectively, information regarding how butternut’s population genetic structure is affected by environmental and historical factors is needed. In this study, we assessed genetic structure and diversity of 161 butternut trees from 19 adjacent watersheds in the southern portion of butternut’s range using 12 microsatellite markers. We assessed the genetic diversity and genetic differentiation among trees grouped at various spatial scales. Our goal was to use historical abundance and land use data for these watersheds, which are now all a part of the Great Smoky Mountains National Park (GSMNP), to understand the ecological and evolutionary forces that challenge the conservation and management of butternut. In general, butternuts within the 19 neighboring watersheds were all part of one continuous population, with gene flow throughout. Significant genetic differentiation was detected between some groups of trees, but the differentiation was quite small and may not represent an ecologically significant distinction. The mean heterozygosity in all watersheds remained high, despite extensive mortality. Overall, genetic diversity and rare alleles were evenly distributed across all watersheds, with some variability in subpopulations containing butternut-Japanese walnut hybrids (Juglans x bixbyi or buarts). These results indicate that management of this species should focus on protection from future hybridization with Japanese walnut, promotion of regeneration, and persistence of all remaining butternut trees, which still retain high levels of genetic diversity.     

High inbreeding and low connectivity among Ambystoma texanum populations in fragmented Ohio forests

Habitat loss and fragmentation negatively impact the size and diversity of many natural populations. Woodland amphibians require connected aquatic and terrestrial habitats to complete their life cycle, and often rely on metapopulation structure for long‐term persistence. Wetland loss and deforestation fragment amphibian populations, which may result in population isolation and its negative effects. The aim of this research was to analyze the population genetic structure of small‐mouthed salamanders (Ambystoma texanum) in western Ohio, where agriculture is now the dominant land use. Salamander tail tissue was collected from eight breeding pools. Three pools occur in the same forest; the other five are in forest patches at distances ranging from 250 m to 20 km from one another. Eight microsatellite loci were amplified by PCR and genotyped for allele size. Observed heterozygosities were lower than expected in all sampled populations; the two most isolated sites (Ha1, Ha2) had the highest inbreeding coefficients. Ha2 also had the lowest mean number of alleles and was found to be genetically differentiated from populations to which our data analysis indicates it was historically connected by gene flow. The most distant site (Ha1) had the highest number of private alleles and showed genetic differentiation from other populations both historically and currently. Geographic distance between pools was strongly correlated with the number of private alleles in a population. The results suggest that population isolation results in decreased genetic diversity and that a breakdown of metapopulation structure due to landscape change may contribute to differentiation between once‐connected populations.     

Patterns of seed dispersal and pollen flow in Quercus garryana (Fagaceae) following post-glacial climatic changes

Aim We examined the genetic structure of Quercus garryana to infer post‐glacial patterns of seed dispersal and pollen flow to test the hypotheses that (1) peripheral populations are genetically distinct from core populations and from one another; (2) genetic diversity declines towards the poleward edge of the species’ range; and (3) genetic diversity in the chloroplast genome, a direct measure of seed dispersal patterns, declines more sharply with increasing latitude than diversity in the nuclear genome. We address our findings in the context of known historical oak distribution from pollen core data derived from previously published research. Location Oak–savanna ecosystems from southern Oregon, USA (core populations/non‐glaciated range) northward to Vancouver Island, British Columbia, Canada (peripheral populations/glaciated range). Methods We genotyped 378 trees from 22 sites with five chloroplast and seven nuclear microsatellite loci. For both sets of markers, we estimated genetic diversity and differentiation using an analysis of molecular variance and generated Mantel correlograms to detect genetic and geographical distance correlations. For the nuclear markers, we also used a Bayesian approach to infer population substructure. Results There was a large degree of population differentiation revealed by six chloroplast haplotypes, with little (≤ 3) or no haplotype diversity within sites. Peripheral island locations shared the same, maternally inherited chloroplast haplotype, whereas locations in mainland Washington had greater haplotype diversity. In contrast, genetic diversity of the nuclear markers was high at all locations sampled. Populations clustered into two groups and were significantly positively correlated over large spatial scales (≤ 200 km), although allele richness decreased significantly with latitude. Population substructure was observed between core and peripheral populations because rare alleles were absent in peripheral localities and common allele frequencies differed. Main conclusions The observed pattern of chloroplast haplotype loss at the northern periphery suggests restricted seed dispersal events from mainland sites to peripheral islands. This pattern was unexpected, however, as refugial oak populations remained near the current post‐glacial range even during the Last Glacial Maximum. Using nuclear markers, we found high within‐population diversity and population differentiation only over large spatial scales, suggesting that pollen flow is relatively high among populations.     

Genetic diversity and morphological differentiation in Liatris helleri (Asteraceae), a threatened plant species

Liatris helleri (Asteraceae) is an insect-pollinated herbaceous perennial endemic to several high-elevation sites in the Blue Ridge Mountains of North Carolina. Allozymes were used to describe the genetic diversity and population structure in nine populations of this rare, federally listed species. Differences in leaf morphology were also examined for greenhouse-grown plants representing several populations. The proportion of the total genetic diversity found among populations, as indicated by the allozyme data, was 16%. Higher levels of population differentiation were found for differences in leaf shape; population of origin accounted for 37% of the variation in maximum leaf width, while families within populations accounted for 7%. In contrast to many endemic species, L. helleri maintains fairly high levels of genetic diversity. For the species, the percent polymorphic loci was 87.5, the average number of alleles at variable loci was 3.00 and the gene diversity was 0.276. Mean population values were percent polymorphic loci =58.4, mean number of alleles per polymorphic locus =2.59 and gene diversity =0.219. The estimated gene flow was low (Nm=0.85–1.32) and a relatively high correlation (r=0.55; p<0.005) was found between linear geographic and genetic distance. This suggests that the populations are partially isolated by distance, despite the limited range (<60 km) of the species. We recommend that population distinetiveness be maintained in restoration efforts.     

中国特有濒危树种毛红椿核心和边缘居群的遗传多样性

选用8对多态的微卫星引物, 研究了毛红椿(Toona ciliata var. pubescens)核心居群和边缘居群的遗传多样性。研究结果显示, 边缘居群的观察等位基因数和有效等位基因数并不比核心居群低, 甚至更高。普通广布和稀有地方等位基因在所有居群中均有分布, 而普通地方和稀有广布等位基因分别仅在5个和3个居群中有分布。从4种类型等位基因总数上看, 边缘居群高于核心居群, 特别是边缘居群的稀有地方等位基因数量明显多于核心居群。边缘居群的平均期望杂合度和观察杂合度都高于核心居群。核心居群间的基因分化系数为0.1520, 边缘居群间为0.3045, 边缘居群与核心居群的遗传分化差异达到显著水平。核心居群间基因流大于1, 而边缘居群间基因流小于1, 说明核心居群间基因交流频繁, 边缘居群由于片段化和地形影响, 基因流较小。Mantel检验结果显示, 居群间遗传距离与地理距离的相关性不显著, 说明地理距离对毛红椿居群遗传分化的影响不显著。