THE SIGNIFICANCE OF GENETIC EROSION IN THE PROCESS OF EXTINCTION. IV. INBREEDING DEPRESSION AND HETEROSIS EFFECTS CAUSED BY SELFING AND OUTCROSSING IN SCABIOSA COLUMBARIA

The effects of self-fertilization, within-population crosses (WPC) and between-population crosses (BPC) on progeny fitness were investigated in the greenhouse for Scabiosa columbaria populations of varying size. Plants grown from field collected seeds were hand pollinated to produce selfed, WPC, and BPC progeny. The performance of these progenies was examined throughout the entire life cycle. The different pollination treatments did not significantly affect germination, seedling-to-adult survival, flowering percentage and the number of flower heads. But severe inbreeding depression was demonstrated for biomass production, root development, adult survival, and seed set. Additionally, multiplicative fitness functions were calculated to compare relative fitnesses for progeny. On average, WPC progeny showed a more than 4-fold, and BPC progeny an almost 10-fold, advantage over selfed progeny, indicating that S. columbaria is highly susceptible to inbreeding. No clear relationship was found between population size and level of inbreeding depression, suggesting that the genetic load has not yet been reduced substantially in the small populations. A significant positive correlation was found between plant dry weight and total fitness. In two out of six populations, the differences between the effects of the pollination treatments on dry weight increased significantly when seedlings were grown under competitive conditions. This result is interpreted as an enhancement of inbreeding depression under these conditions. It is argued that improvement of the genetic exchange between populations may lower the probability of population extinction.     

Genetic diversity and structure in two species of Leavenworthia with self-incompatible and self-compatible populations

Self-fertilization is a common mating system in plants and is known to reduce genetic diversity, increase genetic structure and potentially put populations at greater risk of extinction. In this study, we measured the genetic diversity and structure of two cedar glade endemic species, Leavenworthia alabamica and L. crassa. These species have self-incompatible (SI) and self-compatible (SC) populations and are therefore ideal for understanding how the mating system affects genetic diversity and structure. We found that L. alabamica and L. crassa had high species-level genetic diversity (H_e=0.229 and 0.183, respectively) and high genetic structure among their populations (F_ST=0.45 and 0.36, respectively), but that mean genetic diversity was significantly lower in SC compared with SI populations (SC vs SI, H_e for L. alabamica was 0.065 vs 0.206 and for L. crassa was 0.084 vs 0.189). We also found significant genetic structure using maximum-likelihood clustering methods. These data indicate that the loss of SI leads to the loss of genetic diversity within populations. In addition, we examined genetic distance relationships between SI and SC populations to analyze possible population history and origins of self-compatibility. We find there may have been multiple origins of self-compatibility in L. alabamica and L. crassa. However, further work is required to test this hypothesis. Finally, given their high genetic structure and that individual populations harbor unique alleles, conservation strategies seeking to maximize species-level genetic diversity for these or similar species should protect multiple populations.     

Maintenance of Phenotypic and Genotypic Diversity in Managed Populations of Stenocereus Stellatus (Cactaceae) by Indigenous Peoples in Central Mexico

The columnar cactus Stenocereus stellatus is used in Central Mexico for its edible fruits which are harvested in wild, managed in situ and cultivated populations. Management in situ of wild populations is conducted by selectively sparing and enhancing the abundance of plants with desirable phenotypes when fields are cleared for agricultural use. Cultivation of desirable phenotypes is carried out by vegetative propagation in homegardens. Effects of human management on morphological and genetic variation of S. stellatus were analyzed by comparing morphological diversity indices (MD, based on Simpson’s index) and expected (H_e) heterozygosity indices from allozyme analysis, in wild, managed in situ, and cultivated populations from La Mixteca and the Tehuacán Valley regions. Morphological diversity was similar among regions, but populations from the wetter La Mixteca region averaged higher genetic variation (H_e = 0.279) than populations from Tehuacán (H_e = 0.265). On average, populations manipulated by people had higher levels of variation (MD = 0.479 ± 0.012, H_e = 0.289 in cultivated populations; MD = 0.461 ± 0.014, H_e = 0.270 in managed in situ populations) than wild populations (MD = 0.408 ± 0.017, H_e = 0.253), which is apparently due to a continual introduction and replacement of plant materials in the manipulated populations. The results illustrate that human management may not only maintain but also increase both morphological and genetic diversity of manipulated plant populations in relation to that existing in the wild. Managed in situ and cultivated populations of S. stellatus are important reservoirs of variation, and are crucial for the general maintenance of diversity in wild populations. These populations may play a principal role in designing strategies for the conservation of variation of this cactus.     

The significance of genetic erosion in the process of extinction

Summary The amount of genetic variation within a population is, among other things, related to population size. In small populations loss of genetic variation due to high levels of genetic drift and inbreeding may result in decline of individual fitness and increase the chance of population extinction. This chain of processes is known as genetic erosion. In this study we tested the genetic erosion hypothesis by investigating the relation between morphological variation and population size in two perennial, outbreeding plant species, Salvia pratensis and Scabiosa columbaria. To relate phenotypic variation to genetic variation the experiments were performed under common environmental conditions. For both species a positive correlation was observed between the amount of phenotypic variation and population size (Salvia r=0.915; Scabiosa r=0.703). Part of this variation is likely to have a genetic base, although maternal effects were present in the seedling and juvenile life stages. Differences between populations could in both species be attributed to parameters related to fitness, i.e. growth rate in Salvia and reproductive effort in Scabiosa. Discriminant functions reflecting these parameters did not however discriminate between large and small populations.Results are discussed in relation to the common environment approach and to electrophoretic results obtained earlier (Van Treuren et al. 1991).     

Genetic diversity of an endangered plant, <Emphasis Type="Italic">Cypripedium macranthos</Emphasis> var. <Emphasis Type="Italic">rebunense</Emphasis> (Orchidaceae): background genetic research for future conservation

Cypripedium macranthos var. rebunense is an endangered plant endemic to Rebun Island, Japan. A proper understanding of genetic diversity is needed when conducting conservation programs for rare and endangered species. We therefore examined the genetic diversity of C. macranthos var. rebunense using allozyme markers with a view to future conservation. Our study revealed that C. macranthos var. rebunense has relatively high genetic diversity (P was 0.62, n _a and n _e were 1.85 and 1.28 respectively, and H _o and H _e were 0.163 and 0.187, respectively) when compared with other plant taxa. The natural habitats of C. macranthos var. rebunense are geographically separated into northern and the southern populations. Disappearance of alleles and increase in homozygosity expected as a result of the bottleneck effect were observed, particularly in the southern populations composed of a small number of plants. As additional negative effects (inbreeding depression and further genetic drift) due to fragmentation are predicted in these populations, the southern populations may show deterioration of genetic diversity in the near future.     

Relationships between plant density,outcrossing rates and seed set in natural and experimental populations of Scabiosa columbaria

Outcrossing rates were estimated in both natural and experimental populations of Scabiosa columbaria, a self-compatible, entomophilous, gynodioecious, protandrous perennial. In natural populations, estimates of the outcrossing rate in hermaphrodites were near to one and ranged from 0.84 ± 0.07 to 1.12 ± 0.11. The effect of plant density on outcrossing rates was studied in two experimental populations of 27 individuals. Contrary to expectation the estimates of the outcrossing rate in hermaphrodites were about 100% for both densities. However, in the sparse population, the fraction of developed seeds of plants used to estimate outcrossing rates was significantly lower than of plants in the dense population (0.41 ± 0.06 and 0.68 ± 0.08, respectively). Artificial pollinations of these plants in the greenhouse showed that the fraction of developed seeds was 0.60 ± 0.01 and 0.83 ± 0.05 after self- and cross-pollination, respectively. The combined results suggested that the differential success of self- and cross-pollination might have caused equalization of the outcrossing rates in the experimental populations, despite different plant densities. The implications of the results for conservation biology are discussed.     

A Study of Conservation Genetics in Cupressus chengiana,an Endangered Endemic of China,Using ISSR Markers

ISSR markers were used to analyze the genetic diversity and genetic structure of eight natural populations of Cupressus chengiana in China. ISSR analysis using 10 primers was carried out on 92 different samples. At the species level, 136 polymorphic loci were detected. The percentage of polymorphic bands (PPB) was 99%. Genetic diversity (H _e) was 0.3120, effective number of alleles (A _e) was 1.5236, and Shannon’s information index (I) was 0.4740. At the population level, PPB = 48%, A _e=1.2774, H _e=0.1631, and I=0.2452. Genetic differentiation (G _st) detected by Nei’s genetic diversity analysis suggested 48% occurred among populations. The partitioning of molecular variance by AMOVA analysis indicated significant genetic differentiation within populations (54%) and among populations (46%; P < 0.0003). The average number of individuals exchanged between populations per generation (N _m ) was 0.5436. Samples from the same population clustered in the same population-specific cluster, and two groups of Sichuan and Gansu populations were distinguishable. A significantly positive correlation between genetic and geographic distance was detected (r=0.6701). Human impacts were considered one of the main factors to cause the rarity of C. chengiana, and conservation strategies are suggested based on the genetic characters and field investigation, e.g., protection of wild populations, reestablishment of germplasm bank, and reintroduction of more genetic diversity.     

Genetic diversity of four esterase loci in natural populations of Hordeum spontaneum C. Koch from Jordan

Summary The diversity of four esterase loci was studied electrophoretically in 690 individual spikes representing 12 populations of wild barley (Hordeum spontaneum C. Koch.) collected from central, peripheral and marginal regions of its distribution in Jordan. A minimum of 6, 10, 5 and 5 alleles were observed at the Est-1, Est-2, Est-4 and Est-5 loci, respectively. Est-2 and Est-4 were the most diverse loci (H_c=0.53±0.05 and 0.46±0.07, respectively). Est-5 was intermediate (H_c=0.33+0.07) and Est-1 was the lowest (H_c=0.22±0.04). Polymorphism was highest in the central populations (H_e=0.52±0.04), followed by the peripheral (H_e=0.40±0.05) and the marginal (H_e=0.22±0.05) populations. Average allelic diversity between (G_st=0.49) and within (H_s=0.51) populations reflects a high allelic differentiation among these populations. Log-linear analyses revealed that four two-locus terms and two three-locus terms were significantly associated (P<0.05). Geographical distances between populations were not significantly correlated with Nei's genetic similarity index (r=0.16; P<0.19). It is postulated that diversifying selection is a major factor in the population genetic differentiation of these esterase loci.     

Comparison of genetic (co)variance matrices within and between Scabiosa canescens and S. columbaria

In the current study, we used bootstrap analyses and the common principal component (CPC) method of Flury (1988) to estimate and compare the G ‐matrix of Scabiosa columbaria and S. canescens populations. We found three major patterns in the G ‐matrices: (i) the magnitude of the (co)variances was more variable among characters than among populations, (ii) different populations showed high (co)variance for different characters, and (iii) there was a tendency for S. canescens to have higher genetic (co)variances than S. columbaria. The hypothesis of equal G ‐matrices was rejected in all comparisons and there was no evidence that the matrices differed by a proportional constant in any of the analyses. The two ‘species matrices’ were found to be unrelated, both for raw data and data standardized over populations, and there was significant between‐population variation in the G ‐matrix in both species. Populations of S. canescens showed conservation of structure (principal components) in their G ‐matrices, contrasting with the lack of common structure among the S. columbaria matrices. Given these observations and the results from previous studies, we propose that selection may be responsible for some of the variation between the G ‐matrices, at least in S. columbaria and at the between‐species level.     

Conservation of long-lived perennial forest herbs in an urban context: <Emphasis Type="Italic">Primula elatior</Emphasis> as study case

Urban forests are generally fragmented in small isolated remnants, embedded in an inhospitable human-used matrix, and incur strong anthropogenic pressures (recreational activities, artificialization, pollution and eutrophication). These lead to particularly high constraints even for common forest herbs, whose genetic response may depend on life-history traits and population demographic status. This study investigated genetic variation and structure for 20 allozyme loci in 14 populations of Primula elatior, a self-incompatible long-lived perennial herb, occurring in forest fragments of Brussels urban zone (Belgium), in relation to population size and young plants recruitment rate. Urban populations of P. elatior were not genetically depauperate, but the small populations showed reduced allelic richness. Small populations showing high recruitment rates—and therefore potential rejuvenation—revealed lower genetic diversity (H _o and H _e) than those with low or no recruitment. No such pattern was observed for the large populations. There was a significant genetic differentiation among populations within forest fragments (F _SC = 0.052, P < 0.001), but not between fragments (F _CT = 0.002, P > 0.10). These findings suggest restricted gene flow among populations within fragments and local processes (genetic drift, inbreeding) affecting small populations, strengthened when there is recruitment. Urban forest populations of long-lived perennial herbs can be of conservation value. However, restoration of small populations by increasing population size through regeneration by seedling recruitment may lead to negative genetic consequences. Additional management, aiming to restore gene flow among populations, may need to be applied to compensate the loss of genetic diversity and to reduce inbreeding.     

Grain protein variability among populations of wild barley (Hordeum spontaneum C. Koch.) from Jordan

Summary Protein content, kernel weight, and genetic diversity in the storage protein hordein, encoded by the Hor 1 and Hor 2 loci, were assessed in 12 populations of wild barley (Hordeum spontaneum C. Koch.) collected from central, peripheral, and marginal areas of its distribution in Jordan. Protein content ranged from 106.3 to 239.1 g kg^-1, and kernel weight ranged from 21.17 to 31.8 mg. Populations with high protein content and heavy kernels have been identified. Electrophoretic analysis of the storage protein hordein showed that the two hordein loci, Hor 1 and Hor 2, are highly polymorphic, having 34 and 38 alleles, respectively. Polymorphism (H_e) was highest in central populations (H_e Hor 1=0.859, H_e Hor 2=0.782), intermediate in peripheral populations (H_e Hor 1=0.566, H_e Hor 2=0.509), and lowest in marginal populations (H_e Hor 1=0.392, H_e Hor 2=0.349). Geographical distances between populations were not indicative of Nei's genetic similarity (NI). NI values averaged 0.209 and ranged from 0.0 to 0.83, supporting the hypothesis of an island population model for the species. The high proportion of allelic diversity, apportioned among populations for Hor 1 (0.584) and Hor 2 (0.495) loci, indicates that these natural populations are a rich reserve of genetic variability for protein. This variability is readily exploitable in breeding.     

Morphology and phenology of Scabiosa columbaria from mown and grazed habitats - Results of a simulation experiment

We analysed the morphology and phenology of Scabiosa columbaria in relation to grassland management by mowing and grazing. We selected 12 populations from mown and grazed calcareous grassland in six regions of central Europe. At each population site, we collected seed material to produce plants for a morphological and phenological analysis of the species in a simulation experiment, which comprised three treatments (control, simulated mowing and simulated grazing).The simulation experiment revealed a clear morphological and phenological differentiation of S. columbaria. Plants from the two treatment types differed in size, since individuals from mown sites had longer top peduncles than individuals from grazed sites. Individuals from mown populations flowered earlier than individuals from grazed populations. In the control treatment, individuals from both habitat types produced a similar number of fruiting capitulums. When subjected to simulated mowing, the reproductive success of the individuals was clearly reduced. Plants from mown habitats produced, however, a significantly larger number of fruiting capitulums than plants from grazed habitats. Simulated grazing reduced the reproductive success stronger than simulated mowing but differences between individuals from both habitat types were not significant.The results of our simulation experiment clearly indicate morphological and phenological adaptation of S. columbaria to mowing and grazing. The comparatively young selection pressure of mowing obviously selected early flowering individuals, while the original land use by grazing favoured late flowering plants.     

Genetic Diversity and Population Structure in Chinese Indigenous Poplar (Populus simonii) Populations Using Microsatellite Markers

Populus simonii Carr. is an important ecological and commercial breeding species in northern China; however, human interference during the last few centuries has led to the reduction and fragmentation of natural populations. To evaluate genetic diversity and differentiation within and among existing populations, we used 20 microsatellite markers to examine the genetic variation and structure of 16 natural populations. Our results indicated that the level of genetic diversity differed among populations, with average number of alleles per locus (AR) and expected heterozygosity (H _e) ranging from 3.7 to 6.11 and 0.589 to 0.731, respectively. A marginal population from Qilian in the Qinghai–Tibetan Plateau showed the highest values (AR?=?6.11, H _e?=?0.731), and the Zhangjiakou and Yishui populations showed the lowest values (AR?=?4.08, H _e?=?0.589 and AR?=?3.7, H _e?=?0.604). The inbreeding coefficient (F _IS) values for all populations were positive, which indicated an excess of homozygotes. The microsatellites allowed the identification of a significant subpopulation structure (K?=?3), consistent with an isolation by distance model for P. simonii populations. Additionally, molecular variance analysis revealed that 14.2 % of the variation resided among populations, and 85.8 % could be attributed to variation within populations. These data provide valuable information for natural resource conservation and for optimization of breeding programs in the immediate future.     

北沙柳群体遗传多样性和遗传结构分析

以内蒙古北沙柳(Salix psammophila)国家种质资源库内9个群体(P1~P9)288个无性系为实验材料,利用TP-M13-SSR技术,选取22对具有多态性EST-SSR北沙柳引物,采用毛细管电泳对PCR产物进行检测,分析北沙柳遗传多样性、分化程度和群体遗传结构,为北沙柳种质资源库遗传管理、无性系鉴定、品种选育、遗传改良和构建指纹图谱提供理论依据。结果显示:(1)22对EST-SSR引物共检测到222个等位基因,各位点平均等位基因数(A)为10,四倍体基因型丰富度(G)和特异基因型(G1)总和分别为1 460和802个,平均特异基因型比率(P1)和种质鉴别率(P2)分别为45.86%和13.21%。(2)9个群体平均等位基因数(A)为7.475,基因型丰富度(G)为15.586,观察杂合度(Ho)和期望杂合度(He)分别为0.577和0.638。以期望杂合度He为标准,北沙柳群体遗传多样性水平最低的是P1和P9。(3)北沙柳群体遗传分化系数仅为0.02,AMOVA分子变异分析显示,北沙柳群体大部分遗传变异来自群体内(97%),群体间变异仅为3%。(4)三维主成分、聚类和Structure群体遗传结构分析显示,9个群体被划分为2个组,Mantel检验表明北沙柳遗传距离与地理距离极显著相关(r=0.684 P0.001)。研究表明,北沙柳种质资源具有丰富的遗传多样性,这是其具有耐旱、耐寒、耐高温、耐沙埋和抗风蚀等适应性较强的分子基础;北沙柳的遗传变异集中在群体内;分布区群体呈现由中心向边缘群体扩张分化的趋势。     

Effects of Fragmentation of Evergreen Broad-leaved Forests on Genetic Diversity of Ardisia Crenata var. Bicolor (Myrsinaceae)

Due to the long generation times and high densities, dominant tree species usually did not respond consistently with theoretical predictions to the recent fragmentation. Genetic structures of shrubs and herbs, especially those with low densities, may be more sensitive to forest fragmentation. We studied the genetic structure of a self-compatible subshrub, Ardisia crenata var. bicolor (Myrsinaceae) in a recently fragmented landscape. Ten RAPD primers used for analysis generated a total of 76 bands. We found that A. c. var. bicolor had relatively low species-level (P₉₅ = 63.2%; H = 0.106; Shannon diversity index (SI) = 0.246) and within-population diversity (P₉₅ = 5.3−46.1%; H = 0.026−0.175; SI = 0.032−0.253), and significant population differentiation (G_ST = 0.445). Significantly positive relationships were found between measures of diversity (P₉₅, H and SI) and the log of estimated population size. No significant relationship was observed between Nei's genetic distance and spatial distance of pairwise populations, indicating no isolation-by-distance. Given most species of forests are shrubs and herbs with short generation times, our observation indicated that distinct genetic consequences of recent fragmentation may be expected for quite a number of plant species.     

Fitness in Naturally Occurring and Restored Populations of a Grassland Plant Lychnis flos‐cuculi in a Swiss Agricultural Landscape

Wildflower seed mixtures are widely used for restoration of grasslands. However, the genetic and fitness consequences of using seed mixes have not been fully evaluated. Here, we studied the role of genetic diversity, origin (commercial regional seed mixtures, natural populations), and environmental conditions for the fitness of a grassland species Lychnis flos‐cuculi. First, we examined the relationship between genetic diversity, environmental parameters, and fitness in sown and natural populations of this species in a Swiss agricultural landscape. Second, we established an experiment in the study area and in an experimental garden to study the implications of local adaptation for plant fitness. Third, to examine the response of plants to different soil properties, we conducted an experiment in climate chambers, where we grew plants from sown and natural populations of L. flos‐cuculi as well as from seed suppliers on soils with different nutrient and moisture content. We detected no significant effect of genetic diversity on the fitness of sown and natural populations. There was no clear indication that plants from natural populations were better adapted to local environment than plants from sown populations or seed suppliers. However, plants of natural origin invested more into generative reproduction than plants from sown populations or seed suppliers. Furthermore, in the climate chamber, plants originating from natural populations tended to flower earlier. Our results indicate that using nonlocal seeds for habitat recreation may influence restoration success even if the seeds originate from the same seed zone as the restored site.     

Detection of Low Genetic Variation in a Critically Endangered Chinese Pine, Pinus squamata, Using RAPD and ISSR Markers

With only 32 individuals in the northeastern corner of Yunnan Province, China, Pinus squamata is one of the most endangered conifers in the world. Using two classes of molecular markers, RAPD and ISSR, its very low genetic variation was revealed. Shannon's index of phenotypic diversity (I) was 0.030, the mean effective number of alleles per locus (A_e) was 1.032, the percentage of polymorphic loci (P) was 6.45, and the expected heterozygosity (H_e) was 0.019 at the species level based on RAPD markers. The results of ISSR were consistent with those detected by RAPD but somewhat higher (I = 0.048, A_e = 1.042, P = 12.3, H_e = 0.029). The genetic variation of the subpopulation on the southwest-facing slope was much higher than that of the subpopulation on the northeast-facing slope, which may be attributed to the more diverse environment on the southwest-facing slope. The genetic differentiation between the two subpopulations was very low. The between-subpopulation variabilities, Φ_ST, calculated from RAPD and ISSR data were 0.011 and 0.024. Because of the lack of fossil records and geological historical data, it was difficult to explain the extremely low genetic diversity of the species. We postulate that this ancient pine might have experienced strong bottlenecks during its long evolutionary history, which caused the loss of genetic variation. Genetic drift and inbreeding in post-bottlenecked small populations may be the major forces that contribute to low genetic diversity. Human activities such as logging may have accelerated the loss of genetic diversity in P. squamata.     

DOES MATE LIMITATION IN SELF‐INCOMPATIBLE SPECIES PROMOTE THE EVOLUTION OF SELFING? THE CASE OF LEAVENWORTHIA ALABAMICA

Genetic diversity at the S‐locus controlling self‐incompatibility (SI) is often high because of negative frequency‐dependent selection. In species with highly patchy spatial distributions, genetic drift can overwhelm balancing selection and cause stochastic loss of S‐alleles. Natural selection may favor the breakdown of SI in populations with few S‐alleles because low S‐allele diversity constrains the seed production of self‐incompatible plants. We estimated S‐allele diversity, effective population sizes, and migration rates in Leavenworthia alabamica, a self‐incompatible mustard species restricted to discrete habitat patches in rocky glades. Patterns of polymorphism were investigated at the S‐locus and 15 neutral microsatellites in three large and three small populations with 100‐fold variation in glade size. Populations on larger glades maintained more S‐alleles, but all populations were estimated to harbor at least 20 S‐alleles, and mate availabilities typically exceeded 0.80, which is consistent with little mate limitation in nature. Estimates of the effective size (N_e) in each population ranged from 600 to 1600, and estimated rates of migration (m) ranged from 3 × 10⁻⁴ to nearly 1 × 10⁻³. According to theoretical models, there is limited opportunity for genetic drift to reduce S‐allele diversity in populations with these attributes. Although pollinators or resources limit seed production in small glades, limited S‐allele diversity does not appear to be a factor promoting the incipient breakdown of SI in populations of this species that were studied.     

Analysis of Genetic Diversity and Population Structure in Sophora japonica Linn. in China With Newly Developed SSR Markers

Sophora japonica is a medium-sized deciduous native tree to China. Its flower buds and fruits have special medicinal value. By using 26 highly variable nuclear microsatellites, newly reported here, we assessed the genetic diversity and population structure of 10 representative populations (180 individuals in total) within the species. The results revealed a relatively high genetic diversity in S. japonica (N_a?=?8.00, H_e?=?0.74, PIC?=?0.80, I?=?1.67), and reduced genetic variation and heterozygote excess were detected in landrace populations (N_a?=?5.59, H_e?=?0.71, A_r?=?4.11, F_IS?=???0.043) when compared with those semi-wild population (N_a?=?9.7, H_e?=?0.74, A_r?=?8.80, F_IS?=?0.082). A significant bottleneck was detected in two Landraces populations. Moderate differentiation and frequent gene flow were detected among all populations (F_ST?=?0.079, P?<?0.05, N_m?=?2.893). Mantel test detected a marginal significant pattern of isolation by distance (r?=?0.009, P?=?0.50), and strong differentiation was observed between most southern and northern populations both by the STRUCTURE clustering and principal coordinate analysis (PCoA), indicating that geographic isolation played a key role in the genetic differentiation of the species. The results from this study will benefit the breeding and conservation of S. japonica, other congener species, and tree species with similar life history traits.

     

Land use affects flowering time: seasonal and genetic differentiation in the grassland plant Scabiosa columbaria

Management practices like mowing or grazing have a large impact on grassland species. Due to its evolutionary significance, the interaction between the flowering time of plants and land use is of special interest. Asynchronous flowering restricts gene flow between populations and promotes, as a consequence, their differentiation. We selected 12 populations across southern central Europe to study the impact of mowing and grazing on seasonal and genetic differentiation in the grassland species Scabiosa columbaria. We conducted a common garden experiment to analyse floral display between populations and applied molecular markers to assess genetic diversity and genetic differentiation between populations. We demonstrated explicitly that flowering time and genetic differentiation are linked with the type of land use. Populations from mown habitats flowered significantly earlier than populations from grazed sites. Furthermore, genetic differentiation was stronger between populations from sites of different land use than between populations from far away geographic regions. The results of this study indicate that populations of S. columbaria are seasonally adapted to mowing and grazing. Land use is, therefore, an important factor for evolution in grassland species, which promotes the development of seasonal ecotypes and clearly affects intraspecific variation.