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Results for “variable gene flow”

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At least 19 recordsLinked to original sources

PubMed1991

Genetic variability and gene flow in geographical populations of Ceratitis capitata (Wied.) (medfly).

Two African populations of Ceratitis capitata (Kenya and Réunion Isl.) and two Mediterranean ones (Sardinia and Procida Isl.) have been studied for genetic variability at 25 loci by electrophoresis. Wright's FST, Slatkin's Nm* gene flow estimator, Nei's distance (D) together with measures of variability such as H, P, A have been used to compare the population from Kenya with the other three. Parameters using gene frequencies (FST, D, Nm*) indicate the presence of substantial geographic heterogeneity, largely attributable to genetic drift and correlated with dispersion of the medfly from its source area (Subsaharan Africa) to the periphery. The Kenyan population has high genetic variability (assessed by H, P and A), as might be expected given its native status. Significant gene flow estimates between Kenya and the derived Mediterranean populations supports the hypothesis of recent colonization. Part of the geographic heterogeneity is related to the presence of fixed alleles in the more differentiated Réunion population although it maintains the genetic attributes of the ancestral population. Selection or other forces may have played an important role in the differentiation of this population.

Alleles↗

PubMed1999

Evidence for gene flow between wild and cultivated Medicago sativa (Leguminosae)based on allozyme markers andquantitative traits.

Genetic differentiation between co-occurring crops and their wild relatives will be greatly modified by crop-to-weed gene flow and variation between human and natural selective pressures. The maintenance of original morphological features in most natural populations of Medicago sativa in Spain questions the relative extent of these antagonistic forces. In this paper, we measured and compared the pattern of population differentiation within and among the wild and cultivated gene pool with respect to both allozymes and quantitative traits. Patterns of diversity defined three kinds of natural populations. First, some populations were intermediate with respect to both allozymes and quantitative traits. This suggests that crop-to-weed gene flow may have created hybrid populations in some locations. Second, some populations were different from all the cultivated landraces with respect to both allozymes and quantitative traits. This probably results from variable gene flow in space and in time, due to demographic stochasticity in either natural or cultivated populations. Third, differentiation from cultivated landraces was only achieved for the quantitative traits but not for allozymes in two populations. This suggests that natural selection in some locations may oppose gene flow to establish cultivated traits into the natural introgressed populations.

Journal Article↗

PubMed2001

Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus).

African wild dogs are large, highly mobile carnivores that are known to disperse over considerable distances and are rare throughout much of their geographical range. Consequently, genetic variation within and differentiation between geographically separated populations is predicted to be minimal. We determined the genetic diversity of mitochondrial DNA (mtDNA) control region sequences and microsatellite loci in seven populations of African wild dogs. Analysis of mtDNA nucleotide diversity suggests that, historically, wild dog populations have been small relative to other large carnivores. However, population declines due to recent habitat loss have not caused a dramatic reduction in genetic diversity. We found one historical and eight recent mtDNA genotypes in 280 individuals that defined two highly divergent clades. In contrast to a previous, more limited, mtDNA analysis, sequences from these clades are not geographically restricted to eastern or southern African populations. Rather, we found a large admixture zone spanning populations from Botswana, Zimbabwe and south-eastern Tanzania. Mitochondrial and microsatellite differentiation between populations was significant and unique mtDNA genotypes and alleles characterized the populations. However, gene flow estimates (Nm) based on microsatellite data were generally greater than one migrant per generation. In contrast, gene flow estimates based on the mtDNA control region were lower than expected given differences in the mode of inheritance of mitochondrial and nuclear markers which suggests a male bias in long-distance dispersal.

Africa↗

PubMed2000

Genetic diversity and gene flow in the morphologically variable, rare endemics Begonia dregei and Begonia homonyma (Begoniaceae).

Begonia dregei and B. homonyma (Begoniaceae), rare plants endemic to coastal forests of eastern South Africa, are two closely related species with high levels of variation among populations in the shape of leaves. Distribution of genetic variation and genetic relatedness were investigated in 12 populations of B. dregei and seven of B. homonyma using polyacrylamide gel electrophoresis. Twelve of the 15 enzyme loci examined were polymorphic, but only seven loci were polymorphic within at least one population. Genetic diversity measures indicated that the among-population gene differentiation represents >90% of the total genetic component in both species considered individually or combined. This indicated restricted gene flow, consistent with the limited dispersal abilities of Begonia generally and the ancient separation of isolated forest patches. Genetic distances among populations are much higher than usually found within species. Allozyme data provide no support for the recognition of B. dregei and B. homonyma as distinct species.

Journal Article↗

PubMed1999

Gene flow among habitat patches on a fragmented landscape in the spider argiope trifasciata (Araneae: araneidae)

The banded garden spider (Argiope trifasciata) is a common orb weaver of old field habitats in the United States. In this study, we determined levels of genetic variability and gene flow among seven populations in central Pennsylvania, based on variation at eight allozyme loci. Mean heterozygosity (observed) per population was 7. 5% and mean polymorphism was 39.3%, consistent with levels of variability in other arthropods. Values of GST for the four polymorphic loci (mean GST=0.011) suggest that gene flow prevents the genetic differentiation of these populations. The average number of migrants per generation (Nm) among these populations is estimated to be 31.3. The lack of significant interpopulation genetic differentiation among these disjunct populations may result from spiderling aerial dispersal (ballooning), a more continuous distribution of suitable habitat in the past, and perhaps the use of roadside vegetation as gene flow corridors. On the other hand, the study populations did not exhibit isolation-by-distance, suggesting that suitable habitat in our study area is experienced as less than continuous by A. trifasciata. Thus, although A. trifasciata is an excellent ballooner, ballooning does not confer unlimited access among all populations, which suggests that ballooning may be a far less effective means of long-distance dispersal than previously thought.

Journal Article↗

PubMed1974

Isozyme allelic frequencies related to selection and gene-flow hypotheses.

Significant correlations between allelic frequencies and environmental variables in a number of insect species have been demonstrated by multivariate techniques. Since many environmental variables show a strong relationship to geographic location and since gene flow between populations can also produce patterns of gene frequencies which are related to the geographic location, both selection and gene-flow hypotheses are consistent with the observed correlations. The genetic variables can be corrected for geographic location and so for linear gene-flow patterns. If, after correction, the genetic variables still show significant correlations with similarly corrected environmental variables, then these correlations are consistent with hypotheses of selection but not of gene flow. The data of Johnson and Schaffer (1973) have been reanalyzed using the method of canonical correlation after correction for geographical location by means of multiple regression. Five of the nine loci studied exhibit significant canonical correlations. These results, under the assumption of linear gene flow, support hypotheses of selective action of environmental variables in the genotype-environment relationships observed.

Alleles↗

PubMed1993

HIV induces deletion of T cell receptor variable gene product-specific T cells.

Using a flow cytometric method, CD4+, CD8+, alpha beta TCR+ and TCR variable region gene product (TVRGP)-specific T cells were analysed in healthy heterosexual males (HHeM), HIV-seronegative homosexual males (SNHM), asymptomatic seropositive homosexual males (ASPH) and homosexual males with AIDS who were either well (AIDS-A), or unwell in hospital (AIDS-B). Total CD4+ and CD8+ T cell numbers were similar in HHeM and SNHM. CD4+ T cells were significantly reduced in ASPH relative to both HHeM and SNHM and in AIDS-A and AIDS-B relative to SNHM. TVRGP-specific T cells expressed as a percentage of TCR alpha beta + cells showed no significant difference in HHeM, SNHM and AIDS-B. The proportion of alpha beta + cells expressing the V beta 5.1, V beta 12 and V alpha 2 gene product (GP) was, however, significantly reduced in ASPH and AIDS-B relative to HHeM, SNHM and AIDS-A. Possible causes of TVRGP-specific T cell deletion are discussed.

CD4 Antigens↗

PubMed1994

Isozyme variability of Trypanosoma brucei s.l.: genetic, taxonomic, and epidemiological significance.

Seventy-eight Trypanosoma brucei s.l. stocks from different hosts, representing the three Trypanosoma brucei subspecies and three Trypanosoma evansi stocks, were studied for variation at 18 polymorphic isozyme loci. The results were used to determine the genetic variability among stocks and to estimate gene flow among populations. Total genetic variability in T. brucei s.l. was less than that in Trypanosoma cruzi, the agent of Chagas' disease. Results support a clonal population structure in T. brucei, but do not preclude a hypothesis of occasional mating. However, some natural clones of T. brucei s.l. appear as genetically stable and should be considered as useful taxonomic units in applied studies. Greater genotypic diversity was observed in trypanosomes isolated from wild mammals. Numerical taxonomy methods identified a group of clones representing most of the human stocks from Central and West Africa. This group probably corresponds to Trypanosoma brucei gambiense "group I" (Gibson, Parasitology Today 2, 255-257, 1986). As reported elsewhere, genetic evidence of the subspecies Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense was ambiguous, suggesting that these taxa represent more "nosodemes" rather than actual genetic clades.

Alleles↗

PubMed1999

Major histocompatibility complex (MHC) class II polymorphism and paternity in the monogamous Hypogeomys antimena, the endangered, largest endemic Malagasy rodent.

Sequence variation at a major histocompatibility complex (MHC) class II gene was examined in Hypogeomys antimena, a monogamous endemic rodent of Madagascar. The study was conducted throughout its remaining geographical range (20 x 40 km) by direct sequencing and single-strand conformation polymorphism (SSCP). The objectives of the study were: (i) to investigate levels of polymorphism in the MHC complex of a highly endangered species that experienced a severe reduction in population size; and (ii) to investigate the genetic mating system by assessing the frequency of extra-pair paternity (EPP) as EPP might have important consequences to increase gene flow and, therefore, genetic variability within a population. The amplified gene segment had a very low variability (only two alleles) in H. antimena compared with other mammalian species. The alleles segregated consistently with Mendelian expectations in families. No case of EPP was found. The present data suggest no difference between the social and the genetic mating system.

Animals↗

PubMed2000

Analysis of Clines with Variable Selection and Variable Migration.

We report a likelihood-based method that estimates both dispersal and natural selection using the rate of change of the shape of a cline when selection and migration are not constant through time. We have investigated the case of local adaptation of the mosquito Culex pipiens to organophosphate insecticides in the Montpellier area in France. We have analyzed the modification of the clinal patterns at two resistance loci during the period from breeding to overwintering. We show that mosquitoes migrate extensively from breeding to overwintering sites at a rate that is markedly different from previous estimates made during the breeding season only. This migration is also strongly asymmetrical, which can be explained by different geographical distributions of breeding and overwintering sites, by variation in mosquito density along the transect, or by behavioral biases. We found that the starting time of overwintering is likely to vary between northern and southern populations and that substantial fitness costs are associated with resistance alleles at the two loci during overwintering. These results illustrate how demography and adaptive microevolution can be studied using selected markers. The method provides a framework to use population genetics and statistical models to reveal ecological and evolutionary processes.

asymmetrical gene flow↗

PubMed2001

Population structure and dispersal in the Canary Island caddisfly Mesophylax aspersus (Trichoptera, Limnephilidae).

Population genetic structure of the circum-Mediterranean caddisfly Mesophylax aspersus (Trichoptera, Limnephilidae) on the Canary Islands was investigated by studying allozyme variation at nine putative loci in five populations. Genetic variability, population structure and gene flow were compared with data in the literature for continental taxa to assess the effect of isolation of island populations on the genetic structure. Larvae were collected from streams on the islands of Tenerife (one population), La Gomera (two populations in the same catchment) and La Palma (two populations in different catchments). Genetic variability within populations was high relative to that recorded previously for continental Trichoptera, e.g. mean heterozygosity was 0.119--0.336 (0.035--0.15 in continental taxa). Highly significant population structuring was observed (mean F(ST)=0.250), and there was significant within-population structuring (mean F(IS)=0.098). Populations from the same catchment or island were no more similar than populations from different islands, which suggests that occasional long-distance dispersal, both between and within islands, is the predominant influence on the population structure. This dispersal ability has contributed to the colonization of most permanent streams on the Canary Islands by M. aspersus.

Alleles↗

PubMed2000

Identification of the T-cell receptor alpha variable (TRAV) gene(s) in T-cell malignancies.

Due to the lack of a complete range of monoclonal antibodies (mAb) it is often impossible to rapidly identify by flow cytometry the T-cell receptor variable genes in patients suffering from T-cell malignancies. This applies especially to the alpha variable genes (TRAV), since only very few anti-TcR variable alpha mAb are available. We describe a very rapid method for inverse PCR amplification of the TcR alpha chain without prior purification of the double-stranded cDNA, provide the sequences for appropriate oligonucleotides, and describe a buffer system that dramatically enhances the amplification efficiency as compared to standard conditions.

Buffers↗

PubMed2026

Comparative Population Genomics of Relictual Caribbean Island Gossypium hirsutum.

Gossypium hirsutum is the world's most important source of cotton fibre, yet the diversity and population structure of its wild forms remain largely unexplored. The complex domestication history of G. hirsutum combined with reciprocal introgression with a second domesticated species, G. barbadense, has generated a wealth of morphological forms and feral derivatives of both species and their interspecies recombinants, which collectively are scattered across a large geographic range in arid regions of the Caribbean basin. Here we assessed genetic diversity within and among populations from two Caribbean islands, Puerto Rico (n = 43, five sites) and Guadeloupe (n = 25, one site), which contain putative wild or introgressed forms. Using whole-genome resequencing data and a phylogenomic framework derived from a broader genomic survey, we parsed individuals into feral derivatives and truly wild forms. Feral cottons display uneven levels of genetic and morphological resemblance to domesticated cottons, with diverse patterns of genetic variation and heterozygosity. These patterns are inferred to reflect a complex history of interspecific and intraspecific gene flow that is spatially highly variable in its effects. Wild cottons in both Caribbean islands appear to be relatively inbred, especially the Guadeloupe samples. Our results highlight the dynamics of population demographics in relictual wild cottons that experienced profound genetic bottlenecks associated with repeated habitat destruction superimposed on a natural ecogeographical distribution comprising widely scattered populations. These results have implications for conservation and utilisation of wild diversity in G. hirsutum.

Genetics, Population↗

PubMed1986

Genetic similarity and variability between natural populations and laboratory colonies of North American Boophilus (Acari: Ixodidae).

Four natural populations and 4 laboratory colonies of Boophilus microplus (Canestrini) and a laboratory colony of Boophilus annulatus (Say) were subjected to electrophoretic analysis to determine levels of genetic similarity and genetic variability. Populations of B. microplus exhibited high genetic similarity (I = 0.984 +/- 0.012) indicating that all populations share a relatively undifferentiated gene pool. Host vagility is proposed as an important mechanism promoting gene flow in ectoparasites. Levels of genetic variability for B. microplus (h = 0.092 +/- 0.008; P = 0.330 +/- 0.050) were within levels reported for other arthropods. The average genetic identity of 0.716 +/- 0.013 between B. microplus and B. annulatus is of a level characteristic of sibling species. Diagnostic isozymes between laboratory colonies will facilitate identification of these morphologically similar species.

Alleles↗

PubMed2000

Genetic diversity in tetraploid populations of the endangered daisy Rutidosis leptorrhynchoides and implications for its conservation.

Polyploidy is an important variable in assessing the genetics of endangered plant species. Species consisting of populations with different chromosome numbers pose questions as to the mode of inheritance, relative variability status, population divergence and gene flow. The self-incompatible species Rutidosis leptorrhynchoides (Asteraceae) in south-eastern Australia is a good example. The remnant populations in the northern sector of the species range are diploid, whereas southern ones are either diploid or tetraploid. Allozyme analysis of the tetraploid populations showed tetrasomic inheritance confirming an autopolyploid genetic system, a modest increase in their allelic richness over diploid populations in the same region and a lack of genetic divergence. Conservation and replenishment strategies should take account of these genetic features of mixed ploidy.

Asteraceae↗

PubMed1978

[Variation of the profile phenotype M of alpha-1-chymotrypsine : trial of interpretation (author's transl)].

Cross immunoelectrophoresis of serum A1AT (Pi M) shows "frequent" patterns with M2 less than M6 less than M4. Other "particular" patterns were found with M6 greater than M4 and M6 less than M2. The most often found patterns among the Negroid population in our study appeared dissimilar to that found among Caucasians. The "super-gene" concept and the variability of genetic flow may explain this difference. The "particular" patterns are often found in cord blood samples and in patients with hepatocarcinoma. They show similaritis between embryonic and cancerous processes. These different patterns also agree with the "super-gene" concept.

Carcinoma, Hepatocellular↗

PubMed1996

Riverine barriers and gene flow in Amazonian saddle-back tamarins.

We describe patterns of genotypic and phenotypic variation in saddle-back tamarin (Saguinus fuscicollis) populations along the central and upper Rio Juruá, western Brazilian Amazonia. The genetic data are sequence haplotypes of the mitochondrial cytochrome b gene; phenotypic data are pelage colour variants that define sharply demarcated subspecies of this extremely variable tamarin species. We show that gene flow occurs between adjacent subspecies, but that this phenomenon is restricted to the headwater section of the river, which is consistent with expectations from the riverine barrier hypothesis. In this model, the major first-order tributaries of the Amazon form effective barriers to dispersal, with between-bank gene flow limited to the narrowed sections of headwater streams and parallel divergence increasing along both banks from the headwaters to the mouth of a given river. In meandering rivers such as the Rio Juruá, we suggest passive transfer through river channel dynamics as the main mechanism permitting genetic contact between populations on opposite banks of the river. Finally, we argue that in the case of plant and animal species that are largely restricted to unflooded (terra firme) forests, such as tamarins, seasonally flooded (várzea) forest can operate as a critical additional barrier to between-bank gene flow.

Animals↗

PubMed1999

Genetic and Floral Divergence among Sympatric Populations of Gymnadenia conopsea s.l. (Orchideaceae) with Different Flowering Phenology.

Gymnadenia conopsea s.l. is a common orchid in central Europe, where early- and late-flowering populations can be distinguished. The early-flowering form is recognized as subspecies conopsea and the late-flowering form as subspecies densiflora. The two subspecies can occur in sympatry, but their flowering periods are separated. We investigated whether early- and late-flowering subspecies are genetically differentiated, whether they diverged once or repeatedly, and we tried to identify potential evolutionary forces involved in the divergence of the two subspecies. We used genetic markers to estimate genetic divergence within and among populations of early- and late-flowering G. conopsea, and to reconstruct their evolutionary history. In addition, we assessed morphological variation between subspecies. Allozyme variation indicated that subspecies conopsea was significantly more variable than ssp. densiflora and that gene flow among populations of ssp. conopsea was higher than among populations of ssp. densiflora. Gene flow between subspecies was low, indicating that the difference in flowering phenology represented an effective barrier to gene flow. A neighbor-joining tree based on allozyme frequencies indicated that early- and late- flowering populations did not diverge repeatedly in sympatry. Levels of cpDNA variation were generally low, even between G. conopsea s.l. and Gymnadenia odoratissima, chosen as an outgroup. Four cpDNA haplotypes were found, which differed only in the number of microsatellite repeats. Their distribution among subspecies of G. conopsea s.l. and G. odoratissima indicates that microsatellite haplotypes have evolved repeatedly, and their occurrence in different taxa thus represents a homoplasy. Floral characters were variable within and among populations and subspecies but did not consistently separate early- from late-flowering populations. A weak separation between subspecies was found in vegetative characters that presumably reflected habitat and competitive differences experienced by early- and late-flowering populations.

Journal Article↗