共查询到20条相似文献,搜索用时 31 毫秒
1.
Cheryl L. Morrison Steve W. Ross Martha S. Nizinski Sandra Brooke Johanna Järnegren Rhian G. Waller Robin L. Johnson Tim L. King 《Conservation Genetics》2011,12(3):713-729
Knowledge of the degree to which populations are connected through larval dispersal is imperative to effective management,
yet little is known about larval dispersal ability or population connectivity in Lophelia pertusa, the dominant framework-forming coral on the continental slope in the North Atlantic Ocean. Using nine microsatellite DNA
markers, we assessed the spatial scale and pattern of genetic connectivity across a large portion of the range of L. pertusa in the North Atlantic Ocean. A Bayesian modeling approach found four distinct genetic groupings corresponding to ocean regions:
Gulf of Mexico, coastal southeastern U.S., New England Seamounts, and eastern North Atlantic Ocean. An isolation-by-distance
pattern was supported across the study area. Estimates of pairwise population differentiation were greatest with the deepest
populations, the New England Seamounts (average F
ST = 0.156). Differentiation was intermediate with the eastern North Atlantic populations (F
ST = 0.085), and smallest between southeastern U.S. and Gulf of Mexico populations (F
ST = 0.019), with evidence of admixture off the southeastern Florida peninsula. Connectivity across larger geographic distances
within regions suggests that some larvae are broadly dispersed. Heterozygote deficiencies were detected within the majority
of localities suggesting deviation from random mating. Gene flow between ocean regions appears restricted, thus, the most
effective management scheme for L. pertusa involves regional reserve networks. 相似文献
2.
X. GIRESSE D. TOURVIEILLE DE LABROUHE S. RICHARD‐CERVERA F. DELMOTTE 《Molecular ecology resources》2007,7(6):1363-1365
Twelve expressed sequence tags‐derived markers were isolated from Plasmopara halstedii (Oomycetes), the causal agent of sunflower downy mildew. A total of 25 single nucleotide polymorphisms and five indels were detected by single‐strand conformation polymorphism analysis and developed for high‐throughput genotyping of 32 isolates. There was a high level of genetic diversity (HE = 0.484). Observed heterozygosity ranged from 0 to 0.143 indicating that P. halstedii is probably a selfing species. These markers were also useful in detecting significant genetic variations among French populations (FST = 0.193) and between French and Russian populations (FST = 0.23). Cross‐amplification tests on three closely related species indicated that no loci amplified in other Oomycete species. 相似文献
3.
Landscape features often shape patterns of gene flow and genetic differentiation in plant species. Populations that are small and isolated enough also become subject to genetic drift. We examined patterns of gene flow and differentiation among 12 floodplain populations of the selfing annual jewelweed (Impatiens capensis Meerb.) nested within four river systems and two major watersheds in Wisconsin, USA. Floodplain forests and marshes provide a model system for assessing the effects of habitat fragmentation within agricultural/urban landscapes and for testing whether rivers act to genetically connect dispersed populations. We generated a panel of 12,856 single nucleotide polymorphisms and assessed genetic diversity, differentiation, gene flow, and drift. Clustering methods revealed strong population genetic structure with limited admixture and highly differentiated populations (mean multilocus FST = 0.32, FST’ = 0.33). No signals of isolation by geographic distance or environment emerged, but alleles may flow along rivers given that genetic differentiation increased with river distance. Differentiation also increased in populations with fewer private alleles (R2 = 0.51) and higher local inbreeding (R2 = 0.22). Populations varied greatly in levels of local inbreeding (FIS = 0.2–0.9) and FIS increased in more isolated populations. These results suggest that genetic drift dominates other forces in structuring these Impatiens populations. In rapidly changing environments, species must migrate or genetically adapt. Habitat fragmentation limits both processes, potentially compromising the ability of species to persist in fragmented landscapes. 相似文献
4.
Commiphora wightii is a medicinally important endangered species endemic to the Thar Desert of Rajasthan, India and adjoining areas of Pakistan.
The populations of this species are declining sharply because of its extensive use as a natural herb. Random amplified polymorphic
DNA analysis was conducted to find the genetic variation among 7 populations of C. wightii. Of the 100 random primers screened, 44 primers yielded 220 loci. Statistical analysis indicated low genetic diversity (H
pop = 0.0958; I = 0.1498; mean polymorphic loci = 14.28%), and high genetic differentiation among the populations (G
ST = 0.3990; AMOVA Φ
ST of 0.3390; Bayesian θ
(II) = 0.3002). The low genetic diversity may be due to geographic isolation and restricted gene flow (N
m = 0.7533) between the fragmented populations. Unsustainable utilization of the plant has fragmented the population continuum
which served the purpose of genetic exchange between populations. Mantel’s test was performed which revealed a highly significant
positive correlation between genetic and geographic distance (r
2 = 0.614, P = 0.023) among the populations studied. Low variation can also be attributed to poor seed setting and the slow growth pattern
of the species, which is also an apomict. In UPGMA dendrogram the Commiphora wightii samples were divided into two major and one minor cluster. These findings can serve as a guide to preserving the genetic
resources of this medicinal plant species. 相似文献
5.
Yoshiaki Tsuda Haruo Sawada Takafumi Ohsawa Katsuhiro Nakao Hiroki Nishikawa Yuji Ide 《Tree Genetics & Genomes》2010,6(3):377-387
We evaluated the genetic structure of 16 Betula maximowicziana populations in the Chichibu mountain range, central Japan, located within a 25-km radius; all but two populations were at
altitudes of 1,100–1,400 m. The results indicate the effects of geographic topology on the landscape genetic structure of
the populations and should facilitate the development of local-scale strategies to conserve and manage them. Analyses involving
11 nuclear simple sequence repeat loci showed that most populations had similar intrapopulation genetic diversity parameters.
Population differentiation (F
ST = 0.021, G′ST = 0.033) parameters for the populations examined were low but were relatively high compared to those obtained in a previous
study covering populations in a much larger area with a radius of approximately 1,000 km (F
ST = 0.062, G′ST = 0.102). Three populations (Iriyama, Kanayamasawa, and Nishizawa) were differentiated from the other populations by Monmonier’s
and spatial analysis of molecular variance algorithms or by STRUCTURE analysis. Since a high mountain ridge (nearly 2,000 m)
separates the Kanayamasawa and Nishizawa populations from the other 14 populations and the Kanayamasawa and Nishizawa populations
are themselves separated by another mountain ridge, the genetic structure appears to be partly due to mountain ridges acting
as genetic barriers and restricting gene flow. However, the Iriyama population is genetically different but not separated
by any clear geographic barrier. These results show that the landscape genetic structure is complex in the mountain range
and we need to pay attention, within landscape genetic studies and conservation programs, to geographic barriers and local
population differentiation. 相似文献
6.
Sal (Shorea robusta Gaertn., Dipterocarpaceae) is a wind-pollinated tropical tree species found in southern Asia. We investigated the genetic
diversity and structure at four microsatellites of 15 populations comprising continuous-peripheral and disjunct-peripheral
populations in Nepal. Estimates of genetic diversity (N
A = 8.98, H
O = 0.62, H
E = 0.69) were similar when compared with those of other tropical tree species. A higher level of genetic diversity was observed
in continuous-peripheral populations (N
A = 9.61, H
O = 0.67, H
E = 0.72) as compared to disjunct-peripheral (N
A = 8.04, H
O = 0.55, H
E = 0.64). Population differentiation was higher among disjunct-peripheral populations (F
ST = 0.043) than among continuous peripherals (F
ST = 0.012). There was a significant association between gene flow distances and genetic differentiation (r
2 = 0.128, P ≤ 0.007). No spatial arrangement of populations according to their geographical locations was found. Based on observed genetic
diversity protection of some populations in continuous-peripheral range are suggested for the sustainable conservation of
genetic resources of the species while protection of some disjunct-peripheral populations are also recommended for conserving
rare alleles. 相似文献
7.
Sonneratia paracaseolaris, is a critically endangered mangrove species in China. Using inter-simple sequence repeats (ISSR) markers, we compared the genetic variation of introduced populations with that of natural populations to check whether the genetic diversity has been conserved. At the species level, genetic diversity was relatively high (P = 81.37%, He = 0.2241, and SI = 0.3501). Genetic variation in introduced populations (P = 75.78%, He = 0.2291, and SI = 0.3500) was more than that in natural populations (P = 70.81%, He = 0.1903, and SI = 0.2980). Based on Nei's GST value, more genetic differentiation among natural populations was detected (GST = 0.3591). Our data show that the genetic diversity of S. paracaseolaris was conserved in introduced populations to some extent, however, owing to the small natural populations and the threats they encountered, more plants should be planted to enlarge and restore the populations. 相似文献
8.
Genetic diversity and structure in Fagus crenata were studied by analyzing 14 nuclear microsatellite loci in 23 populations distributed throughout the species’ range. Although
population differentiation was very low (F
ST = 0.027; R
ST = 0.041), both neighbor-joining tree and Bayesian clustering analyses provided clear evidence of genetic divergence between
populations along the Japan Sea (Japan Sea lineage) and Pacific (Pacific lineage) sides of Japan, indicating that physical
barriers to migration and gene flow, notably the mountain ranges separating the populations along the Japan Sea and Pacific
sides, have promoted genetic divergence between these populations. The two lineages of the nuclear genome are generally consistent
with those of the chloroplast genome detected in a previous study, with several discrepancies between the two genomes. Within-population
genetic diversity was generally very high (average H
E = 0.839), but decreased in a clinal fashion from southwest to northeast, largely among populations of the Japan Sea lineage.
This geographical gradient may have resulted from the late-glacial and postglacial recolonization to the northeast, which
led to a loss of within-population genetic diversity due to cumulative founder effects. 相似文献
9.
In this study we evaluated the influence of recent landscape fragmentation on the dynamics of remnant fragments from the Brazilian
Atlantic Forest. This biome is one of the richest in the world and has been extensively deforested and fragmented. We sampled
five populations of the threatened Dalbergia nigra, a tree endemic to the Brazilian Atlantic Forest, two located in a large reserve of continuous forest and three in fragments
of different sizes and levels of disturbance. In order to assess historical changes, considering the longevity of the analyzed
species, 119 adults and 116 saplings were genotyped for six microsatellite loci. Lower levels of genetic diversity were found
in the most impacted fragments when compared to the most preserved population located inside the reserve, and there was significant
genetic structure among the populations studied (pairwise F
ST = 0.031–0.152; pairwise D
EST = 0.039–0.301). However, genetic structure among saplings (F
ST = 0.056; D
EST = 0.231) was significantly lower than among adults (F
ST = 0.088; D
EST = 0.275). Estimates of contemporary gene flow based on assignment tests corroborated this result, suggesting that fragmentation
led to an increase in gene flow. This connectivity among remnant fragments could mitigate the loss of genetic diversity through
a metapopulation dynamic, but the high rate of habitat loss and the unknown long-term genetic effects add uncertainty. These
results, taken together with the presence of private alleles in disturbed populations, highlight the importance of preserving
the extant fragments. 相似文献
10.
Jean‐Baptiste Lamy Christophe Plomion Antoine Kremer Sylvain Delzon 《Molecular ecology》2012,21(23):5646-5655
A key aim of evolutionary biology – inferring the action of natural selection on wild species – can be achieved by comparing neutral genetic differentiation between populations (FST) with quantitative genetic variation (QST). Each of the three possible outcomes of comparisons of QST and FST (QST > FST, QST = FST, QST < FST) is associated with an inference (diversifying selection, genetic drift, uniform selection, respectively). However, published empirical and theoretical studies have focused on the QST > FST outcome. We believe that this reflects the absence of a straightforward biological interpretation of the QST < FST pattern. We here report recent evidence of this neglected evolutionary pattern, provide guidelines to its interpretation as either a canalization phenomenon or a consequence of uniform selection and discuss the significant importance this issue will have for the area of evolutionary biology. 相似文献
11.
Human activities such as fragmentation and selective logging of forests can threaten population viability by modification
of ecological and genetic processes. Using six microsatellite markers, we examined the effects of forest fragmentation and
local disturbance on the genetic diversity and structure of adult trees (N = 110) and seedlings (N = 110) of Prunus africana in Kakamega Forest, western Kenya. Taking samples of adults and seedlings allowed for study of changes in genetic diversity
and structure between generations. Thereby, adults reflect the pattern before and seedlings after intensive human impact.
Overall, we found 105 different alleles in the six loci examined, 97 in adults and 88 in seedlings. Allelic richness and heterozygosity
were significantly lower in seedlings than in adults. Inbreeding increased from adult tree to seedling populations. Genetic
differentiation of adult trees was low (overall F
ST = 0.032), reflecting large population sizes and extensive gene flow in the past. Genetic differentiation of seedlings was
slightly higher (overall F
ST = 0.044) with all of the 28 pairwise F
ST-values being significantly different from zero. These results suggest that human disturbance in Kakamega Forest has significantly
reduced allelic richness and heterozygosity, increased inbreeding and slightly reduced gene flow in P. africana in the past 80–100 years. 相似文献
12.
Do plant populations on distinct inselbergs talk to each other? A case study of genetic connectivity of a bromeliad species in an Ocbil landscape 下载免费PDF全文
Karina Vanessa Hmeljevski Alison Gonçalves Nazareno Marcelo Leandro Bueno Maurício Sedrez dos Reis Rafaela Campostrini Forzza 《Ecology and evolution》2017,7(13):4704-4716
Here, we explore the historical and contemporaneous patterns of connectivity among Encholirium horridum populations located on granitic inselbergs in an Ocbil landscape within the Brazilian Atlantic Forest, using both nuclear and chloroplast microsatellite markers. Beyond to assess the E. horridum population genetic structure, we built species distribution models across four periods (current conditions, mid‐Holocene, Last Glacial Maximum [LGM], and Last Interglacial) and inferred putative dispersal corridors using a least‐cost path analysis to elucidate biogeographic patterns. Overall, high and significant genetic divergence was estimated among populations for both nuclear and plastid DNA (ΦST(n) = 0.463 and ΦST(plastid) = 0.961, respectively, p < .001). For nuclear genome, almost total absence of genetic admixture among populations and very low migration rates were evident, corroborating with the very low estimates of immigration and emigration rates observed among E. horridum populations. Based on the cpDNA results, putative dispersal routes in Sugar Loaf Land across cycles of climatic fluctuations in the Quaternary period revealed that the populations’ connectivity changed little during those events. Genetic analyses highlighted the low genetic connectivity and long‐term persistence of populations, and the founder effect and genetic drift seemed to have been very important processes that shaped the current diversity and genetic structure observed in both genomes. The genetic singularity of each population clearly shows the need for in situ conservation of all of them. 相似文献
13.
Oriental beech (Fagus orientalis Lipsky) is a widespread monoecious and wind-pollinated tree species. It is one of the major components of the Hyrcanian forests
of Iran and it is of both ecological and economical importance. Twelve beech stands were surveyed at 9 chloroplast (cp) and
6 nuclear (n) polymorphic microsatellite loci (simple sequence repeats, SSR) to provide information on distribution of genetic
diversity within and among populations and on gene conservation and silvicultural management of this species. High levels
of genetic differentiation were detected for the chloroplast genome (F
ST = 0.80 and R
ST = 0.95), in sharp contrast to the nuclear genome (F
ST = 0.06, R
ST = 0.05). The analysis of molecular variance (AMOVA) showed that 48% of the total cpSSR variation was attributable to differences
among regions and 30% to differences among populations within regions, suggesting multiple origins of beech populations in
Hyrcanian forests. Nuclear SSRs confirmed the presence of significant differentiation among populations and among geographic
regions, even if, as expected, this was less pronounced than that found with cpSSRs (based on AMOVA, differences among regions
and among populations within regions each contribute 5% to total nSSR variance). A highly significant correlation between
genetic (nSSRs) and geographic distances (R
2 = 0.522) was estimated, thus showing an isolation by distance effect. The application of spatial analysis of molecular variance
(SAMOVA) using both marker data allowed identification of genetically homogeneous groups of populations. Possible applications
of these results for the certification of provenances and/or seed lots and for designing conservation programs are presented
and discussed. 相似文献
14.
Ian Bbole Jin-Liang Zhao Shou-Jie Tang Cyprian Katongo 《Zeitschrift fur angewandte Ichthyologie》2020,36(1):62-74
Oreochromis andersonii and O. macrochir are two important cichlid species native to Southern Africa. We describe in this paper their genetic population structure in the Upper Zambezi River, Kafue River, and Lake Bangweulu representing part of the Congo and Zambezi River Basins. Microsatellite genetic markers were employed to analyse the genetic population structure of the two species using 177 tissue samples. The average allele richness of O. andersonii was higher in the Zambezi River (10.500) than in the Kafue River (9.583) though not statistically different. For O. macrochir, it was highest in the Zambezi River (11.170) followed by the Kafue River (9.781) and least in Lake Bangweulu (7.067) and their differences were significant. The gene diversity indices; gene diversity (hs), observed heterozygosity (HO), expected heterozygosity (HE) were high and similar in O. andersonii populations. However, in O. macrochir HE was significantly lower in Lake Bangweulu (0.678) compared to the Kafue River (0.799) and Zambezi River (0.802) populations. Population differentiation estimated by RST and DEST revealed high differentiation in both species (RST = 0.598, DEST = 0.777 for O. andersonii; RST = 0.379, DEST = 0.710 for O. macrochir). The highest source of variation was among populations (84.71%) for O. andersonii and within populations (67.09%) for O. macrochir. Comparisons of population pairs revealed a close genetic similarity between the Zambezi River and Lake Bangweulu populations of O. macrochir. Bottlenecks were observed in both species using the Two-Phase Model (T.P.M.) indicative of a recent genetic loss or reduction in effective population size. Though our results indicate that the populations of both species still maintain sufficiently high levels of genetic diversity in the sampled areas, the bottlenecks observed are a source of concern. We recommend a more robust study of genetic diversity of these species in all sections of these river systems and that some key conservation sites should be identified to protect the gene pool of these native species. 相似文献
15.
Genetic differentiation among European samples of the arctic‐alpine leaf beetle,Chrysomela lapponica
Salima Machkour‐M’Rabet Patrick Mardulyn Jacques M. Pasteels 《Entomologia Experimentalis et Applicata》2008,129(2):181-188
Genetic differentiation within and among isolated populations of the arctic‐alpine leaf beetle, Chrysomela lapponica L. (Coleoptera: Chrysomelidae), specialized on either Salix L. (Salicaceae) or Betula L. (Betulaceae) species, was assessed by F‐statistics analysis at seven allozyme loci. Beetles were collected on Salix spp. in lowland Finland (four samples), at mid elevation in the Black Forest in Germany (450 m) and the Massif Central in France (two samples, 930–1 300 m), and at high elevation in the French Alps (2 300 m). Beetles sampled in the Czech Republic (650 m) fed on Betula pubescens Ehrh. Larvae feeding on Salix spp. secreted host‐derived salicylaldehyde as major toxin; those feeding on B. pubescens secreted isobutyrates and 2‐methylbutyrates of mixed plant–insect origin. In all samples, a heterozygote deficit was observed (0.120<FIS<0.568), in particular in populations collected at mid or high elevation (FIS>0.4). The estimated mean level of genetic differentiation among all populations was high (FST = 0.276). Differentiation was highly variable between pairs of populations (FST = 0.093–0.455, all significant) without any correlation with geographic distance. The sample collected in the Czech Republic, from the only population on B. pubescens, was not the most divergent. 相似文献
16.
Effect of the Aegean Sea barrier between Europe and Asia on differentiation in Juniperus drupacea (Cupressaceae) 下载免费PDF全文
Karolina Sobierajska Krystyna Boratyńska Anna Jasińska Monika Dering Tolga Ok Bouchra Douaihy Magda Bou Dagher‐Kharrat Ángel Romo Adam Boratyński 《Botanical journal of the Linnean Society. Linnean Society of London》2016,180(3):365-385
Juniperus drupacea is an eastern Mediterranean mountain tree with a disjunct geographical range. We hypothesized that this disjunct occurrence (the Peloponnese in Europe and the Taurus and Lebanon Mountains in Asia) should be reflected in the patterns of genetic and morphological diversity and differentiation. Nuclear microsatellite markers (nSSR) and biometric variables of the cones and seeds were examined on material sampled from four populations in Europe and eight in Asia. The Asian populations were characterized by a higher level of genetic diversity than the European populations. The genetic differentiation among populations was moderate but significant (FST = 0.101, P < 0.001). According to the clustering performed with BAPS, six genetically and geographically groups of populations were found: I and II from the Peloponnese; III from the Taurus Mountains; IV and V from the Anti‐Taurus Mountains; and VI from the Lebanon Mountains. The level of genetic differentiation among these six groups (4.30%, P = 0.012) probably reflects long‐lasting genetic isolation during the Pleistocene, as limited genetic admixture was found. In accordance with genetic analysis, the biometric investigations indicated a high level of morphological divergence between the European and Asian populations of the species, with further differentiation between the populations from the Taurus and Lebanon Mountains. 相似文献
17.
Two chloroplast intergenic spacers (trnD-trnT and rps16-trnK) were used to study the phylogeographical structure of Helianthemum
songaricum in northwestern China, with 12 haplotypes detected. Phylogenetic analysis showed that H. songaricum comprised two lineages, one distributed in the Yili Valley and the other in the western Ordos Plateau. Nested clade phylogeographic
analysis likewise indicated that haplotypes in the Yili Valley and those in the western Ordos Plateau formed sister monophyletic
clades. This lineage split was also supported by AMOVA analysis and the Mantel test. AMOVA showed that 99.41% of variance
in H. songaricum occurred between the two distribution regions, and correlation between genetic differentiation and geographical distances
was significant (r
2 = 0.877, P < 0.0001). All populations in the Yili Valley shared haplotype A with high frequency, and range expansion was detected by
nested clade analysis and strongly supported by negative Fu’s F
S-values, Tajima’s D-values, and mismatch distribution analysis. We speculate that aggravation of the dry and cold climate during the early Quaternary,
combined with plant physiological features, were determining factors contributing to the lineage split, and climate oscillations
most likely led to the Yili range expansion. The high drift load (F
ST = 0.9923, G
ST = 0.663) and inbreeding load (H
S = 0.219) of H. songaricum indicate a significant extinction risk, and protective measures should be taken immediately. 相似文献
18.
Population genetic structure of the endemic rosewoods Dalbergia cochinchinensis and D. oliveri at a regional scale reflects the Indochinese landscape and life‐history traits 下载免费PDF全文
Ida Hartvig Thea So Suchitra Changtragoon Hoa Thi Tran Somsanith Bouamanivong Ida Theilade Erik Dahl Kjær Lene Rostgaard Nielsen 《Ecology and evolution》2018,8(1):530-545
Indochina is a biodiversity hot spot and harbors a high number of endemic species, most of which are poorly studied. This study explores the genetic structure and reproductive system of the threatened endemic timber species Dalbergia cochinchinensis and Dalbergia oliveri using microsatellite data from populations across Indochina and relates it to landscape characteristics and life‐history traits. We found that the major water bodies in the region, Mekong and Tonle Sap, represented barriers to gene flow and that higher levels of genetic diversity were found in populations in the center of the distribution area, particularly in Cambodia. We suggest that this pattern is ancient, reflecting the demographic history of the species and possible location of refugia during earlier time periods with limited forest cover, which was supported by signs of old genetic bottlenecks. The D. oliveri populations had generally high levels of genetic diversity (mean He = 0.73), but also strong genetic differentiation among populations (global GST = 0.13), while D. cochinchinensis had a moderate level of genetic diversity (mean He = 0.55), and an even stronger level of differentiation (global GST = 0.25). These differences in genetic structure can be accounted for by a higher level of gene flow in D. oliveri due to a higher dispersal capacity, but also by the broader distribution area for D. oliveri, and the pioneer characteristics of D. cochinchinensis. This study represents the first detailed analysis of landscape genetics for tree species in Indochina, and the found patterns might be common for other species with similar ecology. 相似文献
19.
20.
The pattern of genetic differentiation between diverging species receives much attention as one of the key observable features of speciation. It has often been suggested that introgression between closely related species occurs commonly where their distributions overlap, leading to their becoming more morphologically and genetically similar, but there are a few opposite results. However, most of these studies have been carried out with animals and separate species; few have looked at intraspecific cases, especially in plants. Here, we conduct a comparative study on patterns of genetic differentiation among populations of two varieties of Oreocharis benthamii in allopatry and sympatry based on ISSR data for 754 individuals from 26 populations, in order to understand the processes leading to speciation. Contrary to expectations, the facultative xenogamy (mixed mating) species O. benthamii has a relatively low genetic diversity within populations (H = 0.1014, I = 0.1528) and high genetic differentiation among populations (GST = 0.5867, ФST = 0.659), as is typically found for selfing species. Genetic variance between the two varieties in sympatric populations (44%, ФST = 0.444) is significantly more than that in allopatric populations (14%, ФST = 0.138). Consistent with the taxonomical delimitation of the two varieties, all sampled individuals of O. benthamii clustered into two genetic groups. Moreover, the genetic structures of populations of both varieties are correlated with their different geographical origins. Our studies show that significant divergence between sympatric populations of the two varieties could be attributed primarily to reinforcement by genetic divergent selection in sympatry where secondary contact had occurred. The major proportion of the genetic variation in outcrossing and mixed mating plants may exist among populations when the populations are distributed in fragmented habitats, due to the paucity of suitable habitat combined with inefficient seed dispersal mechanism and limited pollinator foraging area that may limit the gene flow. 相似文献