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1.
Aster furcatus is a rare species with extremely limited genetic variation at isozyme loci. We utilized crossing experiments and seed set data obtained from natural populations to verify that there is also little allelic variation at the self-incompatibility (S) locus. Seed set in several populations was limited by a low number of S-alleles. Associated with a low number of S-alleles in populations was the dissolution of the incompatibility system, manifest by individual variation in self-compatibility, and by complex dominance relationships among S-alleles. Plant self-compatibility was correlated with mean number of ovules per inflorescence. Thus, self-compatibility appeared to be under partial environmental influence. Computer simulations revealed that the shapes of seed set distribution curves of modeled self-incompatible plant populations depend on the number of incompatibility alleles in the populations. By varying the number of S-alleles in modeled populations, we generated seed set distribution curves similar to those of natural populations. Genetic bottlenecks reduce the number of S-alleles and the proportion of compatible matings in populations of multiallelic self-incompatible species. Self-compatible genotypes are at a selective advantage in populations that lack a sufficient number of S-alleles to produce compatible crosses. Aster furcatus appears to be evolving self-compatibility as a result of bottleneck-induced losses of S-alleles. 相似文献
2.
J-B Leducq V Llaurens V Castric P Saumitou-Laprade O J Hardy X Vekemans 《Heredity》2011,106(2):319-329
The effect of selection on patterns of genetic structure within and between populations may be studied by contrasting observed patterns at the genes targeted by selection with those of unlinked neutral marker loci. Local directional selection on target genes will produce stronger population genetic structure than at neutral loci, whereas the reverse is expected for balancing selection. However, theoretical predictions on the intensity of this signal under precise models of balancing selection are still lacking. Using negative frequency-dependent selection acting on self-incompatibility systems in plants as a model of balancing selection, we investigated the effect of such selection on patterns of spatial genetic structure within a continuous population. Using numerical simulations, we tested the effect of the type of self-incompatibility system, the number of alleles at the self-incompatibility locus and the dominance interactions among them, the extent of gene dispersal, and the immigration rate on spatial genetic structure at the selected locus and at unlinked neutral loci. We confirm that frequency-dependent selection is expected to reduce the extent of spatial genetic structure as compared to neutral loci, particularly in situations with low number of alleles at the self-incompatibility locus, high frequency of codominant interactions among alleles, restricted gene dispersal and restricted immigration from outside populations. Hence the signature of selection on spatial genetic structure is expected to vary across species and populations, and we show that empirical data from the literature as well as data reported here on three natural populations of the herb Arabidopsis halleri confirm these theoretical results. 相似文献
3.
Matthew A. Gitzendanner Carl W. Weekley Charlotte C. Germain-Aubrey Douglas E. Soltis Pamela S. Soltis 《Conservation Genetics》2012,13(1):223-234
Genetic data are often crucial for designing management strategies for rare and endangered species. Ziziphus celata is an endangered sandhill shrub endemic to the Lake Wales Ridge of central Florida. This self-incompatible clonal species
is known from only 14 wild populations, most of which are small (under 100 plants). Focusing on the five populations discovered
in 2007, we evaluate the level of genetic diversity and identify clonal lineages within the wild populations of the species
with a set of microsatellite loci. To account for somatic mutations and genotyping errors, we identified clonal lineages using
a threshold cutoff for pair-wise genetic distances among samples. The microsatellites had up to 18 alleles/locus, and, consistent
with outcrossing, samples were highly heterozygous (average population level H
o
= 0.69). Most populations of Z. celata consist of a single clone, and the most diverse population has only 10 clones. Overall Z. celata comprises 41 multi-locus genotypes, and 30 clonal lineages. With nearly 1,000 recorded plants (595 genotyped) and only 30
clonal lineages, Ziziphus celata is highly clonal: clonal richness, R = 0.049. The pair-wise distance method facilitates identification of clonal lineages, avoiding overestimation of clonal diversity.
In most cases, the samples that grouped into a lineage were one to four plants differing from a surrounding genotype by a
single microsatellite repeat insertion/deletion mutation, consistent with these having arisen via somatic mutations. Our data
will enable managers to incorporate extant diversity from wild populations into ex situ collections. Additionally, our research
demonstrates the utility of microsatellites for conservation of imperiled species, identifying genotypes of high priority
for preservation. 相似文献
4.
We sampled 17 populations of a rare autotetraploid Aster kantoensis (Asteraceae) from three river systems located in central Japan, and studied them for allelic variation at 22 enzyme loci. There was no significant correlation between the actual population size and three genetic diversity parameters, suggesting that the effective population size was very small even for the large populations, i.e., even large populations may still have a high probability of being of recent origin and remain influenced by the founder effect. Compared to other autotetraploid species, the total genetic variation of A. kantoensis is small. The number of alleles and gene diversity of a population were not significantly different among the river systems, although the percentage of polymorphic loci was different. Genetic differentiation among river systems was larger than between populations within the river systems, thereby indicating that gene flow between river systems is small, especially between the Kinu River system and Tama or Sagami River systems. 相似文献
5.
Robert Andrew King Sarah L. Harris Angela Karp Jacqueline H. A. Barker 《Tree Genetics & Genomes》2010,6(2):247-258
We present nine polymorphic di- and tri-nucleotide repeat nuclear microsatellite markers selected specifically for their use
in high throughput studies concerning the dioecious allotetraploid Salix alba–Salix fragilis willow complex. These taxa and their hybrids are difficult to discriminate using morphological characters. Thus, multiplex
reactions were developed for these microsatellite loci and their effectiveness to distinguish individuals, especially hybrids,
and their inheritance patterns in controlled crosses were determined. All loci displayed disomic–monogenic inheritance which
allowed for the genotype data to be analysed as for a diploid organism. The nine loci produced a total of 67 alleles (mean,
7.4 alleles per locus; range, 3–11 alleles) in a reference panel of 57 individuals from two germplasm collections and natural
populations. Gene diversity values (as measured by the expected heterozygosity) ranged from 0.000–0.820. A total of 53 distinct
multilocus genotypes were observed, and ordination analysis revealed three separate clusters corresponding to S. alba, S. fragilis and hybrids. The microsatellite loci described here will be used in population genetic studies to investigate genetic variation,
gene flow, levels of hybridisation and the extent of introgression in natural populations of the S. alba–S. fragilis complex. They are also useful for clonal identification, conservation and sustainable management of germplasm collections,
genetic mapping and the selection of individuals and/or certification of controlled crosses for breeding programmes. 相似文献
6.
Ioannis Ganopoulos Filippos Aravanopoulos Anagnostis Argiriou Athanasios Tsaftaris 《Tree Genetics & Genomes》2012,8(6):1181-1190
Self-incompatibility, a common attribute of plant development, forms a classical paradigm of balancing selection in natural populations, in particular negative frequency-dependent selection. Under negative frequency-dependent selection population genetics theory predicts that the S-locus, being in command of self-incompatibility, keeps numerous alleles in equal frequencies demonstrating a wide allelic range. Moreover, while natural populations exhibit a higher within population genetic diversity, a reduction of population differentiation and increase of effective migration rate is expected in comparison to neutral loci. Allelic frequencies were investigated in terms of distribution and genetic structure at the gametophytic self-incompatibility locus in five wild cherry (Prunus avium L.) populations. Comparisons were also made between the differentiation at the S-locus and at the SSR loci. Theoretical expectations under balancing selection were congruent to the results observed. The S-locus showed broad multiplicity (16 S-alleles), high genetic diversity, and allelic isoplethy. Genetic structure at the self-incompatibility locus was almost four times lower than at 11 nSSR loci. Analysis of molecular variance revealed that only 5?% of the total genetic variation concerns differentiation among populations. In conclusion, the wealth of S-allelic diversity found in natural wild cherry populations in Greece is useful not only in advancing basic population genetics research of self-incompatibility systems in wild cherry but also in the development of breeding programs. 相似文献
7.
Galium catalinense (Rubiaceae) is a perennial shrub consisting of two subspecies endemic to California’s Channel Islands: Galium catalinense subsp. catalinense on Santa Catalina Island, and G. catalinense subsp. acrispum, a state-endangered taxon on San Clemente Island. A long history of overgrazing by introduced herbivores has contributed
to population declines in G. catalinense subsp. acrispum. We surveyed 12 populations throughout the taxon’s range for genetic variation using eight polymorphic microsatellite loci
to determine the genetic impact of this demographic bottleneck. At the taxon level, 65 alleles were identified with an average
of 8.1 alleles per locus, although many alleles were rare; the effective number of alleles per locus averaged 2.6. Expected
heterozygosity was 0.550. Individual populations had between six and eight polymorphic loci, with expected heterozygosities
ranging from 0.36 to 0.60, and effective numbers of alleles ranging from 1.8 to 3.5 per locus. Populations fell into three
or four genetic clusters, depending on type of analysis, which may represent refugia where the populations persisted during
intense herbivory. There is little evidence of genetic bottlenecks or substantial inbreeding within populations. These findings,
coupled with indications of recent migration between populations, suggest that G. catalinense subsp. acrispum is currently unlikely to be endangered by genetic factors, but small population sizes make the taxon vulnerable to future
loss of genetic diversity. Management strategies based on these genetic data, population sizes, and the spatial distribution
of populations are discussed. 相似文献
8.
Plant clonality may greatly reduce effective population size and influence management strategies of rare and endangered species. We examined genetic diversity and the extent of clonality in four populations of the monotypic herbaceous perennial Japonolirion osense, which is one of the most rare flowering plants in Japan. Allozyme analysis revealed moderate levels of genetic variation, and the proportion of polymorphic loci (P=66.7%) was higher than the value for species with similar life-history traits. With four polymorphic loci, 19 multilocus genotypes were observed among 433 aerial shoot samples and 10 (52%) were found only in single populations. The proportion of distinguishable genotypes (PD=0.10) and Simpson's index of diversity (D=0.52) also exhibited moderate levels of genotypic diversity compared to other clonal plants, with genotype frequencies at Hardy-Weinberg equilibrium. The distributions of genotypes were often localized and they were mostly found within a radius of 5 m. Spatial autocorrelation analysis showed that shoot samples located 4 m apart were expected to be genetically independent. The results suggest that the spatial extent of genets was relatively narrow and thus the clonality was not extensive. 相似文献
9.
LAIXIANG XU MINGJING SONG YU GUO FANHUA KONG ZHIBIN ZHANG 《Molecular ecology resources》2007,7(4):617-619
We isolated 25 dinucleotide microsatellite loci from the greater long‐tailed hamster (Tscherskia triton) populations in North China. We developed the amplification conditions of polymerase chain reaction for producing high‐resolution genetic markers for each locus. We found 10 microsatellite loci were highly polymorphic in 90 individual hamsters from three areas of North China, and the number of alleles in each locus varied from three to 11. These markers are potential tools for studying the genetic variation of the natural populations of this species. 相似文献
10.
Fourteen polymorphic microsatellite loci were isolated from Asiatic sand sedge, Carex kobomugi Ohwi (Cyperaceae), a clonal perennial herb predominant in sandy coast vegetation in Japan. Polymorphism was surveyed for 24 ramets within a single population and for eight distinct individuals from six populations. Within a population, between two and eight alleles were found per locus, and expected heterozygosity ranged from 0.041 to 0.720. Among populations, a higher level of polymorphism was observed. The microsatellite loci were shown to be useful for the study of spatial genetic structure at fine scale and genetic differentiation among populations. 相似文献
11.
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. 相似文献
12.
Eight polymorphic microsatellites were developed in the perennial herbaceous Aster amellus L. (Asteraceae) and characterized on three populations from France and Switzerland. The number of alleles ranged between four and 30 depending on the locus, and the mean number of effective alleles was 5.8. The average gene diversity equalled 0.744 (range: 0.419–0.957) and the overall differentiation was found significant (θ = 0.092, P < 0.01). Three loci displayed significant heterozygote deficiencies, which might indicate the presence of null alleles. Amplifications were detected on eight loci in Aster alpinus L. 相似文献
13.
Inheritance Characteristics of Microsatellite DNA Loci in Experimental Families of Japanese Flounder Paralichthys olivaceus 总被引:3,自引:0,他引:3
Allele segregating patterns of microsatellite DNA loci in 5 experimental families of Japanese flounder Paralichthys olivaceus and genotype frequencies for deviation from Hardy-Weinberg expectations (HWE) in natural P. olivaceus populations were studied to assess inheritability. Of the 12 microsatellite loci examined, 1 locus had a possibility of scoring
errors of heterozygous individuals caused by unreproducible polymerase chain reaction amplifications of a particular allele.
At the remaining 11 loci, almost all of alleles were segregated according to Mendelian transmission, and observed genotype
frequencies in natural populations were consistent with HWE. The results demonstrated here would provide useful information
supporting the suitability of these microsatellite loci as inheritable P. olivaceus genetic markers.
Received September 25, 2000; accepted March 1, 2001 相似文献
14.
Hayes PK Barker GL Batley J Beard SJ Handley BA Vacharapiyasophon P Walsby AE 《Antonie van Leeuwenhoek》2002,81(1-4):197-202
We have developed a technique for determining the genetic structure of populations of filamentous cyanobacteria. The sequence
diversity at specific gene loci is first characterised in a range of clonal cultures; subsequent analysis involves individual
trichomes collected directly from natural populations. This technique has been used to examine the population genetic structure
of Nodularia in the Baltic Sea and Planktothrix in Lake Zürich. For Nodularia, studies utilising four polymorphic loci reveal that even though there is a degree of linkage disequilibrium, horizontal
transfer of genetic information has been sufficient to generate many of the possible allelic combinations. Analyses reveal
both spatial and temporal variation in population genetic structure. Other studies of both Nodularia and Planktothrix have shown a correlation between particular alleles at the gvpC locus and the critical pressure of the gas vesicles that accumulate within the cell. We are now investigating how the natural
selection of different gas vesicle phenotypes, imposed by changes in the depth of the upper mixed layer of the water column,
affects the relative success of individual cyanobacteria possessing different gvpC alleles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
J. B. Olsen C. J. Lewis E. J. Kretschmer S. L. Wilson J. E. Seeb 《Molecular ecology resources》2002,2(2):101-103
Spawning aggregations of Pacific herring (Clupea pallasi) often exhibit significant interannual variation in allele frequencies of neutral gene markers. We isolated 14 tetranucleotide microsatellites to examine hypothetical processes that may produce this unique genetic signal. We developed and tested primer pairs for each locus and then estimated locus variability in samples (n = 60) from two populations. The number of alleles per locus ranged from five to 49. The expected heterozygosity across loci and populations ranged from 0.20 to 0.96. These microsatellites will be useful for estimating genetic variation in herring on a fine geographical scale. 相似文献
16.
Many animal populations that are endangered in mainland areas exist in stable island populations, which have the potential
to act as an “ark” in case of mainland population declines. Previous studies have found neutral genetic variation in such
species to be up to an order of magnitude lower in island compared to mainland populations. If low genetic variation is prevalent
across fitness-related loci, this would reduce the effectiveness of island populations as a source of individuals to supplement
declining mainland populations or re-establish extinct mainland populations. One such species, the black-footed rock-wallaby
(Petrogale lateralis lateralis), exists within fragmented mainland populations and small island populations off Western Australia. We examined sequence
variation in this species within a fitness-related locus under positive selection, the MHC class II DAB β1 locus. The mainland populations displayed greater levels of allelic diversity (4–7 alleles) than the island population,
despite being small and isolated, and contained at least two DAB gene copies. The island population displayed low allelic diversity (2 alleles) and fewer alleles per individual in comparison
to mainland populations, and probably possesses only one DAB gene copy. The patterns of DAB diversity suggested that the island population has a markedly lower level of genetic variation than the mainland populations,
in concordance with results from microsatellites (genotyped in a previous study), but preserved unique alleles which were
not found in mainland populations. Where possible, conservation actions should pool individuals from multiple populations,
not only island populations, for translocation programs, and focus on preventing further declines in mainland populations. 相似文献
17.
Using an enriched genomic library, we developed seven (CT)n/(GA)n microsatellite loci for eelgrass Zostera marina L. Enrichment is described and highly recommended for genomes in which microsatellites are rare, such as in many plants. A test for polymorphism was performed on individuals from three geographically separated populations (N = 15/population) and revealed considerable genetic variation. The number of alleles per locus varied between five and 11 and the observed heterozygosities for single loci ranged from 0.16 to 0.81 within populations. Mean allele lengths were markedly different among populations, indicating that the identified loci will be useful in studying population structure in Z. marina. As the frequency of the most abundant multilocus genotype within populations was always < 1%, these loci have sufficient resolving power to address clone size in predominantly vegetatively reproducing populations. 相似文献
18.
Genetic diversity is often considered important for species that inhabit highly disturbed environments to allow for adaptation.
Many variables affect levels of genetic variation; however, the two most influential variables are population size and type
of reproduction. When analyzed separately, both small population size and asexual reproduction can lead to reductions in genetic
variation, although the exact nature of which can be contrasting. Genetic variables such as allelic richness, heterozygosity,
inbreeding coefficient, and population differentiation have opposite predictions depending upon the trait (rarity or clonality)
examined. The goal of this study was to quantify genetic variation and population differentiation in a species that resides
in a highly stochastic environment and is both rare and highly clonal, Spiraea virginiana, and to determine if one trait is more influential genetically than the other. From populations sampled throughout the natural
range of S. virginiana, we used microsatellite loci to estimate overall genetic variation. We also calculated clonal structure within populations,
which included genotypic richness, evenness, and diversity. Gene flow was investigated by quantifying the relationship between
genetic and geographic distances, and population differentiation (θ) among populations. Observed heterozygosity, genotypic richness, and inbreeding coefficients were found to be representative
of high clonal reproduction (averaging 0.505, 0.1, and –0.356, respectively) and the number of alleles within populations
was low (range = 2.0–3.6), being more indicative of rarity. Population differentiation (θ) among populations was high (average = 0.302) and there was no relationship between genetic and geographic distances. By
examining a species that exhibits two traits that both can lead to reduced genetic variation, we may find an enhanced urgency
for conservation. Accurate demographic counts of clonal species are rarely, if ever, possible and genetic exploration for
every species is not feasible. Therefore, the conclusions in this study can be potentially extrapolated to other riparian,
clonal shrubs that share similar biology as S. virginiana. 相似文献
19.
Although high levels of self‐fertilization (>85%) are not uncommon in nature, organisms reproducing entirely through selfing are extremely rare. Predominant selfers are expected to have low genetic diversity because genetic variation is distributed among rather than within lineages and is readily lost through genetic drift. We examined genetic diversity at 22 microsatellite loci in 105 individuals from a population of the semelparous herb Lobelia inflata L. and found (i) no evidence of heterozygosity through outcrossing, yet (ii) high rates of genetic polymorphism (2–4 alleles per locus). Furthermore, this genetic variation among lineages was associated with phenotypic traits (e.g. flower colour, size at first flower). Coupled with previous work characterizing the fitness consequences of reproductive timing, our results suggest that temporal genotype‐by‐environment interaction may maintain genetic variation and, because genetic variation occurs only among lineages, this simple system offers a unique opportunity for future tests of this mechanism. 相似文献
20.
Lorna Maclean Amanda T. Pardini Leslie R. Noble John D. D. Bishop Catherine S. Jones 《Molecular ecology resources》2004,4(2):283-285
We report the isolation of the first dinucleotide microsatellite loci from the clonal ascidian, Diplosoma listerianum. Most repeats were compound and highly interrupted, with flanking sequences containing many small interspersed repetitive regions. Consequently, most primers detected polymerase chain reaction products outside the expected size range, and only five out of 15 primers detected polymorphic single‐locus markers. Characterization of five variable loci from two UK populations revealed three to seven alleles per locus, with observed heterozygosity of 0.00–0.86 and expected heterozygosity of 0.10–0.66. Three loci showed significant heterozygote deficits either because of inbreeding, population substructure or the presence of null alleles. 相似文献