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Results for “variable gene flow”

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PubMed1992

Effects of demographic and ethnohistorical factors on average heterozygosities of South Amerindians.

Recent investigations have shown that average within-Tupi genetic distances differ from within-Carib distances, which is possibly due to differences in effective size of the populations belonging to these two linguistic stocks of South American tribes. The aim of this paper is to verify the influence of demographic factors and of interpopulation contacts on the degree of intragroup genetic variability of 18 South American native groups (eight Carib, seven Tupi, and three Gê). The mean per locus per individual heterozygosity (Hm) was studied for seven polymorphic systems and the distance from the centroid rii on Hm was evaluated with regression analysis according to Harpending and Ward's model. Data on intergroup contacts among the populations since the end of the eighteenth century were collected from an extensive review of the ethnohistorical literature. The level of Hm of the three linguistic stocks did not differ, which suggests a homogeneous within-group variation for these groups. In addition, there was no association between gene diversity and population size. On the other hand, demographic size correlated with rii, which suggest that gene frequencies in groups of larger populations more closely resemble the average gene frequencies of native South Americans. Values of rii differed between the stocks, and the average distance from the centroid of the Carib was about 2.6 times greater than that of the Tupi, in accordance with previous genetic distance analysis. It should also be emphasized that there was an important correlation between mean heterozygosity and the degree of historical intertribal contacts. This constitutes a particularly significant finding, suggesting the basic role of intertribal gene flow of the past two centuries on the level of present genetic variability of South American tribes.

Gene Frequency↗

PubMed1995

T cell development and repertoire of mice expressing a single T cell receptor alpha chain.

We examined T cell development and T cell repertoire in transgenic mice expressing a single T cell receptor (TCR) alpha chain derived from the H-2Db-lymphocytic choriomeningitis virus (LCMV)-specific cytolytic T lymphocyte (CTL) clone P14. To generate these alpha P14 mice, mice transgenic for the P14 TCR alpha chain were backcrossed to TCR alpha-deficient mice. Thymi from alpha P14 mice exhibited a marked decrease of mature CD4+8- and CD8+4- single-positive thymocytes comparable to thymi from TCR alpha-deficient mice. Correspondingly, the number of peripheral T cells was reduced in the CD4 (tenfold) and in the CD8 (twofold) subsets when compared to normal mice. T cells from alpha P14 mice generated a primary anti-LCMV CTL response when stimulated in vitro with LCMV in contrast to normal mice which require priming in vivo; elimination of LCMV in vivo was, however, not improved. Flow cytometric analysis of T cells with V beta-specific antibodies showed a diverse endogenous TCR V beta repertoire. Functional analysis of the T cell repertoire, however, revealed a strongly reduced (30-fold) allogeneic and the absence of a vesicular stomatitis virus-specific CTL response and an impaired ability to provide T cell help for antibody isotype switching. Thus, T cell selection in the thymus was impaired and the T cell repertoire was limited in mice expressing only one type of TCR alpha chain.

Animals↗

PubMed2002

Characterization of Herpesvirus saimiri-transformed T lymphocytes from common variable immunodeficiency patients.

Common variable immunodeficiency (CVID) is a very frequent but heterogeneous syndrome of antibody formation. The primary defect remains unknown, but many reports describe peripheral blood T lymphocyte dysfunctions in a substantial proportion of CVID patients, which may impair T--B cell collaboration. In order to investigate whether such putative defects were intrinsic to T cells or, rather, secondary to quantitative differences in T cell subset distribution, or to other described disorders, we have used Herpesvirus saimiri (HVS) for the targeted transformation of CVID CD4+ and CD8+ T cells and subsequent functional evaluation by flow cytometry of their capacity to generate cell surface (CD154, CD69) or soluble (IL-2, TNF-alpha, IFN-gamma) help after CD3 engagement. Unexpectedly, the results showed that 40 different CVID blood samples exposed to HVS gave rise with a significantly increased frequency to transformed CD4+ T cell lines, compared to 40 age-matched controls (27% versus 3%, P < or = 0.00002) suggesting the existence of a CVID-specific signalling difference which affects CD4+ cell transformation efficiency. The functional analysis of 10 CD4+ and 15 CD8+ pure transformed T cell lines from CVID patients did not reveal any statistically significant difference as compared to controls. However, half of the CD4+ transformed cell lines showed CD154 (but not CD69) induction (mean value of 46.8%) under the lower limit of the normal controls (mean value of 82.4%, P < or = 0.0001). Exactly the same five cell lines showed, in addition, a significantly low induction of IL-2 (P < or = 0.04), but not of TNF-alpha or IFN-gamma. None of these differences were observed in the remaining CD4+ cell lines or in any of the transformed CD8+ cell lines. We conclude that certain CVID patients show selective and intrinsic impairments for the generation of cell surface and soluble help by CD4+ T cells, which may be relevant for B lymphocyte function. The transformed T cell lines will be useful to establish the biochemical mechanisms responsible for the described impairments.

Adolescent↗

PubMed2000

Population structure and mating biology of the polygynous ponerine ant Gnamptogenys striatula in Brazil.

Gnamptogenys striatula is a polygynous ponerine ant, whose colonies contain either several differentiated queens or several gamergates. Population structure, queen mating frequency and deviation from random mating were investigated in a north-eastern Brazilian population. Eight workers from each of 33 queenright colonies and 17 queens and their progeny (20-40 offspring) were genotyped using eight variable microsatellite markers. Population differentiation tests indicated limited gene flow at the scale of several kilometres, and tests of isolation by distance revealed population viscosity at the scale of a few metres. This population structure, together with the frequent colony migrations and fissions observed in the field, suggest that new nests are founded by budding in G. striatula. Genetic data showed that 13 of our 17 queens were single-mated and four were double-mated. The estimation of the range of maximal frequency of double-mated queens in the population was 0.232-0.259, demonstrating that mating frequency is low in G. striatula. The low estimated mean relatedness between the 17 queens and their mates (-0. 04 +/- 0.49) indicated no evidence of inbreeding in G. striatula.

Animals↗

PubMed1996

Demographic genetics of brown trout (Salmo trutta) and estimation of effective population size from temporal change of allele frequencies.

We studied temporal allele frequency shifts over 15 years and estimated the genetically effective size of four natural populations of brown trout (Salmo trutta L.) on the basis of the variation at 14 polymorphic allozyme loci. The allele frequency differences between consecutive cohorts were significant in all four populations. There were no indications of natural selection, and we conclude that random genetic drift is the most likely cause of temporal allele frequency shifts at the loci examined. Effective population sizes were estimated from observed allele frequency shifts among cohorts, taking into consideration the demographic characteristics of each population. The estimated effective sizes of the four populations range from 52 to 480 individuals, and we conclude that the effective size of natural brown trout populations may differ considerably among lakes that are similar in size and other apparent characteristics. In spite of their different effective sizes all four populations have similar levels of genetic variation (average heterozygosity) indicating that excessive loss of genetic variability has been retarded, most likely because of gene flow among neighboring populations.

Alleles↗

PubMed2002

Population structure of Candida albicans, a member of the human flora, as determined by microsatellite loci.

This study examines the macrogeographic population structure of Candida albicans, a yeast commensal of humans, through a population genetic analysis of 5 microsatellite loci in 13 cities. The populations were predominantly clonal with some recombination. About 5% of the genetic variation is between populations and the overall pattern is one of intermediate differentiation. We did not find a single widespread genotype but instead found high, macrogeographic gene flow in these clinical populations; the most common genotype was limited to Atlanta and San Francisco. Homogeneity is evident within large geographic regions, such as Europe, Asia, and the USA, and isolation by distance accounted for 39% of the variation observed. Overall gene flow for a member of the human flora is variable but can be extensive, with an average of 4.5 migrants per generation (N(m)). Eastern hemisphere populations were less divergent than those of the Americas and Caribbean, consistent with the expansion of humans out of the eastern hemisphere.

Alleles↗

PubMed1998

Characterization of the T-cell receptor V-beta repertoire in Kawasaki disease.

Kawasaki disease (KD) is a paediatric multisystem necrotizing vasculitis constituting the most frequent cause of acquired heart disease in childhood. Conflicting data have been reported regarding expanded T-cell populations using particular T-cell receptor (TCR) beta-chain variable (BV) gene segments, suggesting either a superantigen- or a conventional antigen-mediated immune response in this disease. In order to further investigate the role of T lymphocytes, cells were stained with an extensive panel of 21 different TCRBV specific monoclonal antibodies (MoAbs) covering almost 70% of all T-cells. Flow cytometry was employed to analyse the expression of the TCRBV repertoire in the CD4+ and CD8+ subsets separately, and of activation markers, in freshly isolated peripheral blood lymphocytes of 25 Kawasaki disease patients during the acute and convalescent phases of the disease. No abnormal usage of any TCRBV family was found, neither acutely nor during convalescence, compared with a control group of healthy children. However, a significant increase in interleukin-2 receptor (IL-2R)-expressing T lymphocytes restricted to the CD4+ subset was observed in KD patients. Our data confirm a strong immune activation in KD that might be of importance in the pathogenesis of the disease.

Child↗

PubMed2004

Inbreeding and population structure of the potato cyst nematode (Globodera pallida) in its native area (Peru).

The dispersal abilities and the population genetic structure of nematodes living in the soil are poorly known. In the present study, we have pursued these issues in the potato cyst nematode Globodera pallida, which parasitizes potato roots and is indigenous to South America. A hierarchical sampling regime was conducted in Peru to investigate gene flow on regional, field and plant scales. Multilocus genotypes of single individuals were obtained using eight polymorphic microsatellites markers. Large heterozygote deficiencies were observed at most loci. The limited active dispersal of larvae from their cyst, which favours mating between (half) siblings, could be responsible for this pattern. Within fields, as well as among fields within regions (even 35 km apart), low F(ST) values suggest extensive gene flow. Among fields within regions, only 1.5-4.4% genetic variability was observed. Passive dispersal of cysts by natural means (wind, running water, or wild animals) or by anthropogenic means (tillage, movement of infected seed tubers) is probably responsible for the results observed. Among regions, high F(ST) values were observed. Thus long-range dispersal (more than 320 km apart) is probably limited by major biogeographical barriers such as the mountains found in the Andean Cordillera. These results provide useful information for the management of resistant varieties, to slow down the emergence and spread of resistance-breaking pathotypes.

Analysis of Variance↗

PubMed1989

Genic differentiation and origin of Robertsonian populations of the house mouse (Mus musculus domesticus Rutty).

This paper examines the relation between chromosomal and nuclear-gene divergence in 28 wild populations of the house mouse semi-species, Mus musculus domesticus, in Western Europe and North Africa. Besides describing the karyotypes of 15 of these populations and comparing them to those of 13 populations for which such information was already known, it reports the results of an electrophoretic survey of proteins encoded by 34 nuclear loci in all 28 populations. Karyotypic variation in this taxon involves only centric (or Robertsonian) fusions which often differ in arm combination and number between chromosomal races. The electrophoretic analysis showed that the amount of genic variation within Robertsonian (Rb) populations was similar to that for all-acrocentric populations, i.e. bearing the standard karyotype. Moreover, divergence between the two types of populations was extremely low. These results imply that centric fusions in mice have not modified either the level or the nature of genic variability. The genetic similarity between Rb and all-acrocentric populations is not attributed to the persistence of gene flow, since multiple fusions cause marked reproductive isolation. Rather, we attribute this extreme similarity to the very recent origin of chromosomal races in Europe. Furthermore, genic diversity measures suggest that geographically separated Rb populations have in situ and independent origins. Thus, Rb translocations are probably not unique events, but originated repeatedly. Two models are presented to explain how the rapid fixation of a series of chromosomal rearrangements can occur in a population without lowering variability in the nuclear genes. The first model assumes that chromosomal mutation rates are between 10(-3) and 10(-4) and that populations underwent a series of transient bottlenecks in which the effective population size did not fall below 35. In the second model, genic variability is restored following severe bottlenecks, through gene flow and recombination.

Animals↗

PubMed2004

Population history of native groups in pre- and postcontact Spanish Florida: aggregation, gene flow, and genetic drift on the Southeastern U.S. Atlantic coast.

Evolutionary trends and population history and structure are discussed for a series of late prehistoric and historic-period skeletal samples from the Georgia coast and interior (the Guale). Phenotypic dental measurement data were collected for nine samples from the late prehistoric (AD 1200-1400) and historic (AD 1608-1702) periods and subjected to population genetic and statistical analyses. The primary trends were for an increase in tooth size through time, and for an initial increase in dental variability in the early historic period, followed by a subsequent decline in dental variability in the late historic period. Given the increasing stress levels, evidenced by previous bioarchaeological analyses (Larsen [2001] Bioarchaeology of Spanish Florida, Gainesville: University Press of Florida), an environmental explanation for the increase in tooth size is unlikely. It is proposed that the early historic period witnessed aggregation and gene flow with extraregional populations, possibly African slaves or nonlocal Native American population groups. The late historic period may have experienced significant loss of phenotypic variability due to genetic drift. In both time periods, the evolutionary mechanism increased average tooth size, with independent variance effects.Because microevolutionary trends obscure patterns of gene flow and population ancestry, the data were detrended following Konigsberg ([1990a] Hum. Biol. 62:49-70), and submitted to standard population genetic analyses (Relethford et al. [1997] Hum. Biol. 69:443-465). Analysis of the precontact samples in isolation (Irene Mound, Irene Mortuary, and an aggregate coastal sample) indicated little genetic microdifferentiation (F(ST) = 0.008), limited extralocal gene flow, and a small distinction between interior and coastal samples. The inclusion of the historic data dramatically increased variability levels (F(ST) = 0.019). The analysis of extralocal gene flow indicates that the late mission period experienced significantly less external gene flow, which is consistent with historic models that suggest the social organization of the Guale during this time period may have been significantly altered. Genetic distances also indicate a primary division between inland and coastal precontact samples and a maintenance of biological populations along the coast. In other words, the coastal, early historic, and late historic period samples are phenotypically homogeneous, supporting the notion that the mission populations were drawn from the local population base. The late mission period sample was also, however, more closely related to the interior samples. This may suggest that the late mission period population was an aggregate sample composed of both remnant interior and coastal population groups.

Colonialism↗

PubMed1995

Enzyme polymorphism among Triatoma infestans (Hemiptera: Reduviidae) colonies.

Allozyme variability in populations of the Chagas's disease vector Triatoma infestans (Klug) was investigated by means of starch gel electrophoresis. Samples were taken from nine laboratory colonies established with individuals collected at different localities across the range of this insect in South America. Zymograms for proteins coded by a total of 17 loci were obtained. Allele frequencies, proportion of polymorphic loci (P), mean heterozygosity per locus (H), similarity (S), and identity (I) indices, genetic distance (D), and gene flow among populations were estimated. Mean values for P = 58.53% and for H = 0.095, indicating an important level of genetic variability. There was remarkable similarity among the colonies (mean I = 0.9946). Estimated gene flow among populations was high. However, on the basis of the known natural history of T. infestans, the uniformity of allele frequencies among populations may be interpreted as the result of the recent and rapid dispersal of the species from the site of origin in the Cochabamba Valley, Bolivia.

Alleles↗

PubMed2000

Gene flow in the European corn borer Ostrinia nubilalis: implications for the sustainability of transgenic insecticidal maize.

Strategies proposed for delaying resistance to Bacillus thuringiensis toxins expressed by transgenic maize require intense gene flow between individuals that grew on transgenic and on normal (referred to as refuges) plants. To investigate gene flow in the European corn borer, Ostrinia nubilalis (Hübner), the genetic variability at 29 sampled sites from France was studied by comparing allozyme frequencies at six polymorphic loci. Almost no deviations from Hardy-Weinberg expectations occurred, and a high stability of allelic distribution was found among samples collected in the same site over two or three different generations, indicating a high stability of the genetic structure over time. The overall genetic differentiation was low at the region and whole country level, suggesting a high and homogeneous gene flow. These results are discussed in relation to the sustainability of transgenic insecticidal maize.

Animals↗

PubMed2006

Population genetics of Collisella subrugosa (Patellogastropoda: Acmaeidae): evidence of two scales of population structure.

Marine invertebrate populations usually show high levels of genetic variability that has frequently been associated with spatial and temporal environmental heterogeneity. One of the most heterogeneous marine environments is the intertidal zone, the habitat of Collisella subrugosa, the most widespread and abundant Brazilian limpet. C. subrugosa has planktonic larvae that can disperse over long distances, what can promote gene flow among shores, working against interpopulational differentiation. In this study we investigated the genetic variability and populational substructure of C. subrugosa through analysis of 24 allozyme loci in 14 samples (590 individuals) collected along 2,700 km of the Brazilian coast. The genetic variability was high ([Formula: see text] and [Formula: see text]), as expected for intertidal species. Genetic differentiation among samples was low (F (ST) = 0.03) what may reflect intensive gene flow associated with larval dispersal. However, we detected an isolation-by-distance pattern of population substructure in one sampled region. High levels of heterozygote deficiency were also observed for many loci in each sample. Alternative hypothesis are discussed, and the "breeding groups" is suggested to explain these pattern, indicating the main cause as environmental heterogeneity.

Animals↗

PubMed2006

Genetic diversity and the reproductive system in related species of antirrhinum.

BACKGROUND AND AIMS: Seven related species of Antirrhinum (A. siculum, A. majus, A. latifolium, A. linkianum, A. litigiosum, A. cirrhigherum and A. tortuosum) were studied in order to compare levels of genetic variation and its partitioning in them, and to check relationships between genetic patterns and the reproductive system. METHODS: Eight hundred and fifty-one plants were screened for variability at 13 allozyme loci by means of horizontal starch gel electrophoresis. Parameters of genetic diversity and its partitioning, the inbreeding coefficient as well as an indirect estimate of gene flow based on the equation: Nm = (1 - G(ST))/4G(ST), were calculated. KEY RESULTS: Genetic variability in A. siculum was found to be the lowest known in the genus. Mean values of F(IT) and F(IS) were mostly positive and not significantly different from zero. Population differentiation (F(ST)) ranged between 6.1 in A. tortuosum and 17.6 in A. linkianum. The inbreeding coefficient within populations ranged between F(IS) = -0.5 in A. tortuosum and F(IS) = 1 in A. siculum. Estimates of gene flow ranged between Nm = 15 in A. majus (considered as very high) to Nm = 0.42 in A. siculum (considered as low). CONCLUSIONS: Correlation was found between levels of diversity and differentiation on one hand, and the reproductive system of the studied taxa on the other. Striking differences among species in the inbreeding coefficient (F(IS)) show different reproductive systems, which mostly support previous reports. Strategies for the conservation of A. siculum are recommended, such as preservation of natural populations as well as ex situ preservation of seeds from different populations.

Antirrhinum↗

PubMed1973

Genic variability and strategies of adaptation in animals.

Levels of genic heterozygosity, as measured by surveys of allozymic variation, are much lower in populations of large, mobile animals (most vertebrates) than in those of small, relatively immobile animals (most invertebrates). This difference is not consistent with theories relating variability to population size (species number) or dispersal ability (gene flow), but it is predicted by Levins' theory of adaptive strategies in relation to environmental uncertainty ("grain"). Mobility and degree of homeostatic control apparently are important factors influencing levels of genic heterozygosity in natural populations. The results argue indirectly that at least a major proportion of allozymic variation is maintained by natural selection.

Adaptation, Biological↗

PubMed1999

Short report: microsatellite sequences as markers for population genetic studies of the mosquito Aedes aegypti, the vector of dengue viruses.

We report the isolation of microsatellites from an enriched library of genomic repeated sequences, using a biotin-labeled oligonucleotide bound to streptavidin-coated magnetic particles. Four microsatellites were obtained from a partial library of 120 recombinant clones. This more efficient and rapid method to obtain these specific repeated sequences is preferred to the conventional isolation procedure based on the construction of a genomic library. Microsatellite markers would be promising molecular tools for the study of genetic variability of mosquito populations. Analyses of genetic structure and gene flow would provide information on the distance, direction and rate of dispersal of genes in Aedes aegypti populations. Knowledge on gene dispersal patterns is required to develop vector control strategies.

Aedes↗

PubMed2004

Phylogeography of Varicorhinus barbatulus (Cyprinidae) in Taiwan based on nucleotide variation of mtDNA and allozymes.

The phylogeographical patterns and population genetic structures of Varicorhinus barbatulus in Taiwan were investigated based on genetic diversity of 34 allozyme loci and nucleotide sequences of 3' end of the cytochrome b gene, tRNA genes, D-loop control region, and the 5' end of the 12S rRNA of mtDNA. Allozyme and mtDNA analyses revealing evident geographical structuring suggest limited gene flow between populations (F(ST)=0.511 and 0.791, respectively). Low genetic variability within populations (P=5.56%; He=0.018) based on allozymes and significantly negative Tajima's D statistics based on mtDNA suggest that most populations in Taiwan may have originated from a small number of founders followed by demographic expansion. The gene genealogy of mtDNA identified six lineages corresponding to major drainages that were separated by the geological barriers due to vicariant events. A minimum spanning network based on nucleotide substitutions reflects divergence from populations of the Miao-li Plateau to northern and southern regions of the island. In contrast to a previous hypothesis that suggests an early invasion to eastern part of Taiwan prior to the lifting of central mountain range some one million years ago, the mtDNA genealogy and molecular dating reveal very recent colonization of the eastern population. Nested clade analyses revealing significant associations between genetic structure and geographical division identify past fragmentation and range expansion as major phylogeographical events that shaped the geographical distribution of this species in Taiwan.

Animals↗

PubMed2000

Genetic structure and AFLP variation of remnant populations in the rare plant Pedicularis palustris (Scrophulariaceae) and its relation to population size and reproductive components.

We investigated plant reproduction in relation to genetic structure, population size, and habitat quality in 13 populations of the rare biennial plant Pedicularis palustris with 3-28500 flowering individuals. We used AFLP (amplified fragment length polymorphism) profiles to analyze genetic similarities among 129 individuals (3-15 per population). In a cluster analysis of genetic similarities most individuals (67%) were arranged in population-specific clusters. Analysis of molecular variance indicated significant genetic differentiation among populations and among and within subpopulations (P < 0.001). Gene flow (N(e) m) was low (0.298). On average, plants produced 55 capsules, 17 seeds per fruit, and 42 seedlings in the following growing season. The number of seeds per capsule was independent of population size and of genetic variability. In contrast, the number of capsules per plant (P < 0.05) and the number of seedlings per plant (P < 0.05) were positively correlated with population size. The relation between population size and the number of seeds per plant was not significant (P = 0.075). The number of capsules and of seeds and seedlings per plant (P < 0.01) were positively correlated with genetic variability. Genetic variability was independent of actual population size, suggesting that historical population processes have to be taken into account, too. Stepwise multiple regressions revealed additional significant relationships of habitat parameters (soil pH, C:N ratio), vegetation composition, and standing crop on reproductive components. We conclude that populations of P. palustris are genetically isolated and that reproductive success most likely is influenced by population size, genetic variability, and habitat quality. Management strategies such as moderate grazing, mowing, and artificial gene flow should endeavor to increase population size as well as genetic variation.

Journal Article↗