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At least 865 records · Page 48Linked to original sources
PubMed1999

Population structure of recrudescent Plasmodium falciparum isolates from western Uganda.

It has been proposed that polymorphisms of the Merozoite Surface Protein 1 and 2 (MSP1 and MSP2) and the Glutamate Rich Protein (GLURP) genes can be considered as genetic markers for the genotyping of field populations of Plasmodium falciparum. During a field study on in vivo drug resistance against chloroquine, sulphadoxine/pyrimethamine (S/P) and cotrimoxazole in West Uganda, sensitive and resistant isolates were collected from patients by fingerprick for genotyping. 59 (72.8%) of the 81 P. falciparum samples isolated at day 0 showed multiclonal infection with 2-7 clones. Among the isolates we investigated, presence of the allelic family MAD20 of MSP1 at day 0 was significantly (P = 0.0041) associated with decreased resistance to antimalarials. Use of this method in a field study on in vivo drug resistance demonstrates another potential application of genotyping as a tool for epidemiological investigations.

Adolescent↗
PubMed1999

The use of microsatellite variation to infer population structure and demographic history in a natural model system.

To assess the reliability of genetic markers it is important to compare inferences that are based on them to a priori expectations. In this article we present an analysis of microsatellite variation within and among populations of island foxes (Urocyon littoralis) on California's Channel Islands. We first show that microsatellite variation at a moderate number of loci (19) can provide an essentially perfect description of the boundaries between populations and an accurate representation of their historical relationships. We also show that the pattern of variation across unlinked microsatellite loci can be used to test whether population size has been constant or increasing. Application of these approaches to the island fox system indicates that microsatellite variation may carry considerably more information about population history than is currently being used.

Animals↗
PubMed2005

Azospirillum brasilense does not affect population structure of specific rhizobacterial communities of inoculated maize (Zea mays).

Positive response of plant species to plant growth-promoting rhizobacteria have led to an increased interest in their use as bacterial inoculants. However, the introduction of exogenous bacteria into natural ecosystems may perturb bacterial populations within the microbial community and lead to the disruption of indigenous populations performing key functional roles. In this study the effect of Azospirillum brasilense inoculation on maize (Zea mays) rhizosphere Actinobacteria, Bacteroidetes, alpha-Proteobacteria, Pseudomonas and Bdellovibrio spp. was assessed using a polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) approach in conjunction with group-specific primers. The DGGE fingerprints analysis revealed that the introduction of A. brasilense did not alter or disrupt the microbial system at the group-specific level. However, some communities such as the alpha-Proteobacteria and Bdellovibrio were influenced by plant age while the other bacterial groups remained unaffected. Based on these as well as previous data, it can be inferred that inoculation with A. brasilense does not perturb the natural bacterial populations investigated.

Azospirillum brasilense↗
PubMed1997

Population structure and physiological changes within a hot spring microbial mat community following disturbance.

The influence of disturbance on a hot spring cyanobacterial mat community was investigated by physically removing the top 3.0 mm, which included the entire cyanobacterial layer. Changes in 16S rRNA-defined populations were monitored by denaturing gradient gel electrophoresis analysis of PCR-amplified 16S rRNA gene segments. Some previously absent cyanobacterial populations colonized the disturbed areas, while some populations which were present before the disturbance remained absent for up to 40 days. Changes in physiological activity were measured by oxygen microelectrode analyses and by 14CO2 incorporation into cyanobacterial molecular components. These investigations indicated substantial differences between the disturbed and undisturbed mats, including an unexplained light-induced oxygen consumption in the freshly exposed mat, increased carbon partitioning by phototrophs into growth-related macromolecules, bimodal vertical photosynthesis profiles, and delayed recovery of respiration relative to photosynthesis.

Cyanobacteria↗
PubMed1992

Transmission pattern and intraspecific competition as determinants of population structure in pinworms (Oxyurida: Nematoda).

The transmission pattern of Zonothrix columbianus (Nematoda: Oxyurida) in its host Tropisternus columbianus (Coleoptera: Hydrophilidae), an aquatic beetle, was studied to determine whether parasites were dispersed with their hosts and to examine the possible role of intraspecific competition in limiting population size. Beetles were sampled at regular intervals from fall 1986 through fall 1989 and examined for worms. Worms, absent in larval stages of the host, were uncommon in newly metamorphosed beetles and therefore probably do not infect adult stages until after they have dispersed; worms are not dispersed with the host. Prevalence reached its lowest points in spring and fall when newly metamorphosed beetles were most common, but it was near 100% for most of the year. Worms were uniformly distributed in the host population. Many hosts had exactly 1 male and 1 female worm; the high prevalence suggests that this infrahost population results from interference competition between males on the one hand and females on the other. Only 3 of 285 beetles contained more than 1 male. Females shared the host with members of the same sex more commonly than males, but females from hosts harboring more than 1 female had significantly fewer eggs than lone females in hosts. Numbers of adult stages of beetles were estimated during spring, summer, and fall of 1989 and were lower in early spring and late fall. Because worms do not disperse with hosts, the panmictic unit could be estimated from the number of infected beetles; this probably was about 50 individuals during the winter bottleneck.

Analysis of Variance↗
PubMed1997

Population structure of Mya arenaria along the New England coastline.

Sequences of the internal transcribed spacer (ITS-1) ribosomal DNA region were compared among 88 soft-shell clams (Mya arenaria) from 12 sites (within three general areas) along the New England coast to determine whether populations were genetically heterogeneous. Two sequence variants were observed, with type 1 having a 3-nucleotide insertion and one point mutation relative to type 2. Allele-specific polymerase chain reaction (PCR); using primers specific to each sequence type, was performed to determine the distribution of individuals who had both allelic forms. DNA from soft-shell clams collected from three areas (Cobscook Bay, Maine; Gulf of Maine; and southern New England) were compared chi 2 analyses of allele-specific PCR results revealed no significant heterogeneity among the three population distributions.

Alleles↗
PubMed2005

Influence of population structure on the consumption of systemic antibiotics.

The high level of consumption of systemic antibiotics in our country prompted a study of factors affecting the geographical variations in this consumption. Several parameters explain the uneven distribution of consumption: (a) the epidemiology of the infections, (b) population-dependent factors and (c) factors dependent on the prescribing doctor. The aim of this study was to study population-dependent parameters (type of population and age). A retrospective longitudinal study was made from antibiotic consumption data provided by International Marketing Services (IMS) between 1 January 1996 and 31 December 2000. The consumption indicator used was the number of defined daily doses per 1000 inhabitants per day (DID). Global consumption in regions under study varied by 5.7 DID: Medina del Campo (25.9 DID), Valladolid city (23.4 DID), Laguna de Duero (22.6 DID), Northern Region (22.4 DID), Southern Region (21.4 DID) and lastly Central Region (20.2 DID). The specific consumption per area showed a greater consumption of amoxicillin in the three urban areas, amoxicillin-clavulanic acid and the main macrolides in Medina del Campo, quinolones antibiotics in the Northern Region and tetracyclines and sulphonamides in Valladolid City. Significant area-dependent global consumption differences were observed with the most marked in urban areas. The differences were more marked when studying the geographical distribution of consumption of the commonly used antibiotics.

Adolescent↗
PubMed1989

Population structure and seasonal intra-burrow movement of Ornithodoros turicata (Acari: Argasidae) in gopher tortoise burrows.

Burrows of the gopher tortoise, Gopherus polyphemus Daudin, were sampled for Ornithodoros turicata (Dugès) infestation using carbon dioxide baits and vacuum extraction. Ticks were captured, marked, released, and recaptured, and population estimates were made using the Lincoln index. Estimated population ranged from 47 to 1,338 ticks per burrow. The tick population consisted predominantly of nymphs, with a significant increase in the larval population during the months of June and July. Adult sex ratio was slightly male-biased, but numbers of adults collected were consistently low. Ticks exhibited a low interburrow movement, but depth preferences fluctuated with season; more ticks occurred in the upper strata of the burrows during the hot, humid months.

African Swine Fever↗
PubMed1982

Population structure in Biomphalaria glabrata: examination of an hypothesis for the patchy distribution of susceptibility to schistosomes.

It has been suggested that the patchy distribution of snail susceptibility to schistosomes might be due to genetic drift. Since direct estimation of genes for susceptibility is not feasible in population studies, electrophoretic techniques were used to examine this hypothesis for populations of Biomphalaria glabrata from Puerto Rico. These populations were characterized by relative genetic homogeneity within populations and differentiation among local populations. The data presented are consistent with the hypothesis that random genetic drift and low rates of migration might be responsible for the patchy distribution of small susceptibility to schistosomes.

Animals↗
PubMed2006

A comparison of variability and population structure for major histocompatibility complex and microsatellite loci in California coastal steelhead (Oncorhynchus mykiss Walbaum).

The major histocompatibility complex (MHC) contains genes integral to immune response in vertebrates. MHC genes have been shown to be under selection in a number of vertebrate taxa, making them intriguing for population genetic studies. We have conducted a survey of genetic variation in an MHC class II gene for steelhead trout from 24 sites in coastal California and compared this variation to that observed at 16 presumably neutral microsatellite loci. A high amount of allelic variation was observed at the MHC when compared to previously published studies on other Pacific salmonids. Elevated nonsynonymous substitutions, relative to synonymous substitutions, were detected at the MHC gene, indicating the signature of historical balancing selection. The MHC data were tested for correlations to and deviations from the patterns found with the microsatellite data. Estimates of allelic richness for the MHC gene and for the microsatellites were positively correlated, as were estimates of population differentiation (F(ST)). An analysis for F(ST) outliers indicates that the MHC locus has an elevated F(ST) relative to the neutral expectation, although a significant result was found for only one particular geographical subgroup. Relatively uniform allele frequency distributions were detected in four populations, although this finding may be partially due to recent population bottlenecks. These results indicate that, at the scale studied here, drift and migration play a major role in the observed geographical variability of MHC genes in steelhead, and that contemporary selection is relatively weak and difficult to detect.

Alleles↗
PubMed1999

Microsatellite and morphological analysis of population structure in the parthenogenetic freshwater snail Melanoides tuberculata: insights into the creation of clonal variability.

The distribution of variability was studied at various geographical scales in the tropical freshwater snail Melanoides tuberculata, in order to analyse the role of factors shaping this distribution, including the mating system and population dynamics. This parthenogenetic polyploid species reproduces mainly asexually, with males occurring at low frequency. About 800 individuals (38 sites) were sampled from Africa and the Middle East, where the species originated, and from recently colonized habitats in South and Central America, and especially the island of Martinique. We first described variation of general aspects and ornamentation of the shells. This analysis confirms the existence of discrete morphs. Second, individuals were studied at three microsatellite loci, showing that each morph is a genetic clone with some minor variation compatible with models of microsatellite evolution. The genetic analysis also showed much more variation within than between clones. However, two populations from Africa exhibited a large amount of variability, and a mixture of sexual and asexual reproduction might explain these genetic patterns. The worldwide distribution of variability is, therefore, compatible with the African origin of the species, and the introduction of a few clones in other parts of the world. These results also suggest that the distribution of variability in Martinique is influenced by flooding events, and that two morphs from Martinique can be interpreted as hybrids between two pre-existing morphs, based on morphological, genetic and geographical arguments.

Journal Article↗