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PubMedDate not supplied

Modulation of complement resistance and virulence of Naegleria fowleri amoebae by alterations in growth media.

Highly-pathogenic, mouse-passaged Naegleria fowleri amoebae are complement resistant. The present study evaluates the effect of complement on N. fowleri and the virulence of the amoebae after animal passage and growth in two different axenic media. Pathogenic N. fowleri maintained in "enriched" Cline medium are virulent for mice and resistant to complement lysis. A rapid decline in resistance to complement and virulence for mice is observed when highly-pathogenic N. fowleri are grown in Nelson medium lacking hemin. N. fowleri maintained in Nelson medium can be rendered complement-resistant by shifting the amoebae to growth in Cline medium for 2 h prior to the addition of complement. Cycloheximide treatment of N. fowleri maintained in Nelson medium blocks the transition to a complement-resistant phenotype following a shift in growth medium. Proteins were radiolabeled with [35S] during a shift from Nelson to Cline medium to identify specific polypeptides which may be associated with the functional activities related to virulence and resistance to complement.

Animals↗
PubMed1995

Cocultivation of the amoeba Naegleria fowleri and the amoebicin- producing strain Bacillus licheniformis M-4.

Antagonism between Bacillus licheniformis M-4 and the pathogenic amoeba Naegleria fowleri HB-1 during cocultivation was influenced by the composition of the medium and the initial amoeba/bacterium ratio. While a ratio of 50 caused complete lysis of amoebae in soil extract with 0.3% glucose (SEG) before 72 h, this ratio had to be at least 12-fold lower in order to obtain similar results in Cline medium. Sporulation of B. licheniformis M-4 took place much earlier in SEG. Amoebicin production was stimulated by the presence of amoebae by either shortening the time of production (as in SEG) or increasing the amount of amoebicins released (as in Cline medium). Electron microscopy showed that amoebae cocultivated in the Cline medium contained bacteria enclosed in digestive vacuoles, while amoebae from SEG cocultures did not.

Amebicides↗
PubMed2005

Differential susceptibility to hypertension is due to selection during the out-of-Africa expansion.

Hypertension is a leading cause of stroke, heart disease, and kidney failure. The genetic basis of blood pressure variation is largely unknown but is likely to involve genes that influence renal salt handling and arterial vessel tone. Here we argue that susceptibility to hypertension is ancestral and that differential susceptibility to hypertension is due to differential exposure to selection pressures during the out-of-Africa expansion. The most important selection pressure was climate, which produced a latitudinal cline in heat adaptation and, therefore, hypertension susceptibility. Consistent with this hypothesis, we show that ecological variables, such as latitude, temperature, and rainfall, explain worldwide variation in heat adaptation as defined by seven functional alleles in five genes involved in blood pressure regulation. The latitudinal cline in heat adaptation is consistent worldwide and is largely unmatched by latitudinal clines in short tandem repeat markers, control single nucleotide polymorphisms, or non-functional single nucleotide polymorphisms within the five genes. In addition, we show that latitude and one of these alleles, GNB3 (G protein beta3 subunit) 825T, account for a major portion of worldwide variation in blood pressure. These results suggest that the current epidemic of hypertension is due to exposures of the modern period interacting with ancestral susceptibility. Modern populations differ in susceptibility to these new exposures, however, such that those from hot environments are more susceptible to hypertension than populations from cold environments. This differential susceptibility is likely due to our history of adaptation to climate.

Acclimatization↗
PubMed2005

Strong selection against hybrids at a hybrid zone in the Ensatina ring species complex and its evolutionary implications.

The analysis of interactions between lineages at varying levels of genetic divergence can provide insights into the process of speciation through the accumulation of incompatible mutations. Ring species, and especially the Ensatina eschscholtzii system exemplify this approach. The plethodontid salamanders E. eschscholtzii xanthoptica and E. eschscholtzii platensis hybridize in the central Sierran foothills of California. We compared the genetic structure across two transects (southern and northern Calaveras Co.), one of which was resampled over 20 years, and examined diagnostic molecular markers (eight allozyme loci and mitochondrial DNA) and a diagnostic quantitative trait (color pattern). Key results across all studies were: (1) cline centers for all markers were coincident and the zones were narrow, with width estimates of 730 m to 2000 m; (2) cline centers at the northern Calaveras transect were coincident between 1981 and 2001, demonstrating repeatability over five generations; (3) there were very few if any putative F1s, but a relatively high number of backcrossed individuals in the central portion of transects; and (4) we found substantial linkage disequilibrium in all three studies and strong heterozygote deficit both in northern Calaveras, in 2001, and southern Calaveras. Both linkage disequilibrium and heterozygote deficit showed maximum values near the center of the zones. Using estimates of cline width and dispersal, we infer strong selection against hybrids. This is sufficient to promote accumulation of differences at loci that are neutral or under divergent selection, but would still allow for introgression of adaptive alleles. The evidence for strong but incomplete isolation across this centrally located contact is consistent with theory suggesting a gradual increase in postzygotic incompatibility between allopatric populations subject to divergent selection and reinforces the value of Ensatina as a system for the study of divergence and speciation at multiple stages.

Animals↗
PubMed2006

When Rensch meets Bergmann: does sexual size dimorphism change systematically with latitude?

Bergmann's and Rensch's rules describe common large-scale patterns of body size variation, but their underlying causes remain elusive. Bergmann's rule states that organisms are larger at higher latitudes (or in colder climates). Rensch's rule states that male body size varies (or evolutionarily diverges) more than female body size among species, resulting in slopes greater than one when male size is regressed on female size. We use published studies of sex-specific latitudinal body size clines in vertebrates and invertebrates to investigate patterns equivalent to Rensch's rule among populations within species and to evaluate their possible relation to Bergmann's rule. Consistent with previous studies, we found a continuum of Bergmann (larger at higher latitudes: 58 species) and converse Bergmann body size clines (larger at lower latitudes: 40 species). Ignoring latitude, male size was more variable than female size in only 55 of 98 species, suggesting that intraspecific variation in sexual size dimorphism does not generally conform to Rensch's rule. In contrast, in a significant majority of species (66 of 98) male latitudinal body size clines were steeper than those of females. This pattern is consistent with a latitudinal version of Rensch's rule, and suggests that some factor that varies systematically with latitude is responsible for producing Rensch's rule among populations within species. Identifying the underlying mechanisms will require studies quantifying latitudinal variation in sex-specific natural and sexual selection on body size.

Animals↗
PubMed1990

Population genetic studies on Jews. I. The alpha 2HS serum glycoprotein, a polymorphism strongly correlated with latitude.

A sample of Jews subdivided according to the birth-place of their parents or grand-parents have been examined for a large number of genetic markers in the course of a long-term project on the genetics of Jews. We report here the findings concerning 794 Jews studied for the AHSG polymorphism. All the subsamples were in Hardy-Weinberg equilibrium. A highly significant difference was found between Sephardic + Near East Jews and Ashkenazi (AHSG*2 frequencies: 0.184 +/- 0.015 and 0.258 +/- 0.016, respectively). For comparative purposes the data available on Caucasoids have been considered. It turned out that they were neatly arranged along a latitude-AHSG gene frequency cline (0.0092 of AHSG*2 gene frequency increase per degree of increase of latitude) in the explored 30 degrees-60 degrees range (r = 0.97; P much less than 0.001). Of the two Jewish frequencies that could be taken into consideration because of their sufficient sizes, that of the Near East + Sephardic Jews was perfectly in line with the above mentioned cline, while that of the Ashkenazi was somewhat displaced in the sense of being more similar than expected to the other, more southern, Jewish group. Since the only AHSG*2 frequency significantly displaced from the regression line is that of the Ashkenazi, whose ancestors lived until centuries ago in more southern areas, this finding is a strong confirmation of the observed cline.

Africa↗
PubMed1996

Distinguishing between primary and secondary intergradation among morphologically differentiated populations of Anolis marmoratus.

Distinguishing between primary and secondary intergradation among differentiated populations, and the relative importance of drift and selection, are persistent problems in evolutionary biology. An historical perspective on population interactions can provide insight into the nature of contacts, and thus help resolve these questions. Continuously distributed populations of Anolis marmoratus from the island of Basse Terre in the Guadeloupean archipelago of the Lesser Antilles show a striking degree of geographic variation in morphology. Initial surveys of mtDNA variation from throughout the Guadeloupean Archipelago revealed one case where levels of sequence difference and phylogenetic relationships of alleles from morphologically differentiated populations from the east coast of Basse Terre were consistent with primary intergradation. In this paper, I examine the genetic population structure of a series of populations spanning this north-south cline in morphological variation to test the hypothesis of primary intergradation. Sequences of the mitochondrial cytochrome-b gene from 50 individuals representing five populations spanning the cline were obtained and fourteen unique haplotypes (differing by 2% or less) were detected. Patterns of nucleotide substitution among haplotypes do not deviate from neutral expectation indicating no effect of selection at the level of mtDNA sequences. Estimates of population structure and gene flow were made using both summary statistics for nucleotide diversity (Nst) and cladistic methods. The results are sensitive to the choice of gene flow model, and this is discussed in detail. Mitochondrial variation in the northern populations may not be at equilibrium, and the phylogeny of alleles is consistent with a recent increase in effective population size. Estimates of nucleotide diversity, gene flow, and the phylogenetic relationships of haplotypes indicate that the southern-most population (representing the extreme of morphological variation along this cline) has been relatively isolated from populations to the north and has experienced a reduced effective population size. The apparent clinal variation between the southern population and the others may therefore reflect secondary contact and introgression rather than primary intergradation.

Animals↗
PubMed1996

Dependence of growth, metabolic expression, and pathogenicity of Naegleria fowleri on exogenous porphyrins.

The pathogenicity of the free-living amoeba Naegleria fowleri is modulated by the composition of the medium used for cultivation. The constituents that determine the level of pathogenicity of N. fowleri, however, have not been definitively established. The present study examined the effects of selected porphyrins on N. fowleri amoebae. The iron-containing porphyrins, hemin or hematin, or the iron-free porphyrin, protoporphyrin IX, were effective in supporting growth of N. fowleri in Cline medium lacking serum. Iron-binding proteins, including hemoglobin, could not satisfy the growth requirement of the amoebae for exogenous porphyrin. Expression of biological functions including azocaseinase activity, agglutination, mobility, complement susceptibility, and virulence were altered by the composition of the growth medium. Amoebae grown in Cline medium supplemented with either hemin or protoporphyrin IX displayed greater mobility and were more resistant to lysis by complement than those grown in Nelson medium. Similarly, amoebae grown in Cline medium supplemented with either hemin or protoporphyrin IX were more pathogenic for B6C3F1 mice than those grown in Nelson medium. The addition of protoporphyrin IX to Nelson medium resulted in a modest increase in mobility, resistance to complement lysis and virulence when compared to N. fowleri amoebae grown in Nelson medium without added porphyrin.

Agglutination↗
PubMed1996

Further note on possible changes in the geographic distribution of ABO and RH blood groups in Great Britain.

We previously reported the tendency for the clines of blood group distributions in England, Scotland, and Wales to become flatter as the result of internal migration. The data came from a one-week birth cohort followed for 16 years. A further seven years and a finer geographic analysis yield mixed results. The Rh- clines did become flatter, but the clines for ABO blood groups A and O showed the opposite tendency during the additional years.

ABO Blood-Group System↗
PubMed2025

Patterns of Genomic Divergence and Introgression in Two Primulina Hybrid Zones.

Hybrid zones have long been promoted as natural laboratories for understanding the mechanisms of speciation. Multiple or replicated hybrid zones are particularly informative, as they allow for assessing the consistency of genomic divergence and introgression across different environmental contexts and demographic histories, thereby improving our understanding of the factors that drive or hinder speciation on a broader scale. Here, using whole-genome resequencing data, we compare the patterns of genomic divergence and introgression in two Primulina hybrid zones. We found that genomic divergence in both hybrid zones is largely shaped by neutral processes, with only a few genomic regions showing signatures of balancing or lineage-specific selection. Genomic cline analyses identified numerous SNPs that showed significantly steeper clines and biased centres than the genome-wide expectation in both hybrid zones, consistent with the existence of reproductive barriers. Within regions of restricted gene flow, we identified 21 genes shared between the two hybrid zones. Annotation of gene function revealed that several genes are involved in reproductive processes. In addition, many zone-specific outlier loci were linked to genes associated with pollen and flower development, suggesting that these barriers may contribute to reproductive isolation under localised ecological conditions. Overall, these findings suggest that while certain reproductive barriers remain consistent across independent hybrid zones, others may be contingent on local environmental contexts. Our results demonstrate that both general and zone-specific mechanisms contribute to reproductive isolation in Primulina, providing empirical evidence that some genomic barriers recur across independent hybrid zones while others arise through localised adaptation.

Lamiales↗
PubMed1991

Chronic application of NMDA decreases the NMDA sensitivity of the evoked tectal potential in the frog.

The activity-dependent mechanism that refines the topography of the retinotectal projection in frogs is mediated by the NMDA receptor. Earlier studies found that chronic treatment of the optic tectum with the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (DL-AP5) desegregated eye-specific stripes in three-eyed frogs, while chronic treatment with NMDA sharpened stripe borders (Cline et al., 1987; Cline and Constantine-Paton, 1990). We now report that this same chronic treatment with NMDA decreases the electro-physiologically measured sensitivity of the optic tectum to applied NMDA: acute application of a given concentration of NMDA decreased the evoked tectal potential to a lesser extent in animals chronically treated with NMDA than it did in normal and sham-treated animals. This is observed as a shift to the right in the NMDA dose-response curves for both the positive and negative postsynaptic components of the evoked tectal response. We believe that this decreased NMDA receptor effectiveness further restricts the intermingling of axon branches from the two eyes by limiting synapse stabilization to areas where afferent activity is most correlated. This would account for the anatomical sharpening of stripe borders (i.e., increased afferent segregation). Quantitative autoradiographic analysis of 3H-glutamate binding to NMDA receptors indicated that binding densities within the tectum did not differ between control groups and NMDA chronically treated groups. We suggest that in the experimental animals the response to NMDA may be decreased by a change in the effectiveness of individual NMDA receptors rather than by decreases in receptor number. This experimentally induced change may be analogous to naturally occurring decreases in receptor function that correlate with the end of some periods of visual plasticity in mammals.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

Exploring northeast African metric craniofacial variation at the individual level: a comparative study using principal components analysis.

A principal components analysis was carried out on male crania from the northeast quadrant of Africa and selected European and other African series. Individuals, not predefined groups, were the units of study, while nevertheless keeping group membership in evidence. The first principal component seems to largely capture "size" variation in crania from all of the regions. The same general morphometric trends were found to exist within the African and European crania, although there was some broad separation along a cline. Anatomically, the second principal component captures predominant trends denoting a broader to narrower nasal aperture combined with a similar shape change in the maxilla, an inverse relation between face-base lengths ("projection") and base breadths, and a decrease in anterior base length relative to base breadth. The third principal component broadly describes trends within Africa and Europe: specifically, a change from a combination of a relatively narrower face and longer vault, to one of a wider face and shorter vault; it shows the northeast quadrant Africans along a cline with the other Africans. Stated in relative terms, the northeastern Africans tend to exhibit narrower bases in relationship to more projecting faces, and broader nasal areas than Europeans, although there is range of variation. Relative to the other African groups, they have narrower nasal areas and narrower faces in relationship to vault length. The crania from the northeast quadrant of Africa collectively demonstrate the greatest pattern of overlap with both Europeans and other Africans. Variation was found to be high in all series but greatest in the African material as a whole. Individuals from different geographical regions frequently plotted near each other, revealing aspects of variation at the level of individuals that is obscured by concentrating on the most distinctive facial traits once used to construct "types." The high level of African interindividual variation in craniometric pattern is reminiscent of the great level of molecular diversity found in Africa. These results, coupled with those of Y chromosome studies, may help generate hypotheses concerning the length of time over which recent craniometric variation emerged in Africa.

Africa↗
PubMed1994

Genetic variation in North Africa and Eurasia: neolithic demic diffusion vs. Paleolithic colonisation.

The hypothesis that both genetic and linguistic similarities among Eurasian and North African populations are due to demic diffusion of neolithic farmers is tested against a wide database of allele frequencies. Demic diffusion of farming and languages from the Near East should have determined clines in areas defined by linguistic criteria; the alternative hypothesis of cultural transmission does not predict clines. Spatial autocorrelation analysis shows significant gradients in three of the four linguistic families supposedly affected by neolithic demic diffusion; the Afroasiatic family is the exception. Many such gradients are not observed when populations are jointly analyzed, regardless of linguistic classification. This is incompatible with the hypothesis that major cultural transformations in Eurasia (diffusion of related languages and spread of agriculture) took place without major demographic changes. The model of demic diffusion seems therefore to provide a mechanism explaining coevolution of linguistic and biological traits in much of the Old World. Archaeological, linguistic, and genetic evidence agree in suggesting a multidirectional process of gene flow from the Near East in the neolithic. However, the possibility should be envisaged that some allele frequency patterns can predate the neolithic and depend on the initial spread of Homo sapiens sapiens from Africa into Eurasia.

Agriculture↗
PubMedDate not supplied

Population genetics of factor V Leiden in Europe.

We have analyzed 5971 control individuals originating from 26 geographically defined populations in Europe and neighboring countries for the presence of factor V Leiden, an important genetic risk factor in venous thromboembolism. The mean frequency of the mutation in the populations studied is 0.027%, with a peak value incidence of more than 12% in Cyprus; the mutation is absent in Inuits and is at low incidence in French Basques. A west to east increasing cline of allele factor V Leiden prevalence (r = 0.479, p < 0.02) was observed in Europe, together with a decreasing south to north cline (r = -0.801, p < 0.001) of these values-but in this last situation only when southwest populations are excluded from the analysis. Based on these findings, an interpretation is proposed of the history of factor V Leiden expansion in Europe during the Neolithic period, from a probable Anatolian center of origin in Turkey.

Europe↗
PubMed1978

Biochemical genetics of Fundulus heterolitus (L.). I. Temporal and spatial variation in gene frequencies of Ldh-B, Mdh-A, Gpi-B, and Pgm-A.

Natural populations of Fundulus heteroclitus show extensive spatial variation in gene frequencies at four unlinked polymorphic loci. Large clinal changes in gene frequencies were found for Ldh-B, Mdh-A, and Gpi-B, whereas the spatial variation for the Pgm-B locus was small. Since the geographical area over which these clines are found is characterized by a steep thermal gradient, the clines in gene frequency are correlated with a directional change in mean water temperature. Maximum gene diversity of these four loci was correlated with annual fluctuations in water temperature. Temporal stability of the allelic frequencies was established for a 2--4 year period.

Animals↗
PubMed1975

Genetic polymorphism in the bladder campion, Silene maritima.

A survey of protein variability has been made in wild populations of Silene maritima, a perennial outcrossing coastal plant. In the most extensively studied populations, at Beesands, six out of 21 loci were polymorphic, and the average heterozygosity was 0.153. Four polymorphic loci were studied on an extensive shingle beach at Dungeness. Three loci showed no frequency cline with distance from the sea; a fourth locus, that for adenylate kinase, showed a barely significant cline, which was not confirmed by a repeat study in the same place a year later. Five polymorphic loci were studied at Beesands along a strip of shingle beach and up a contiguous cliff. No frequency difference between the two habitats was observed. There are significant differences in allelic frequencies between localities. It is concluded that the data fail to show an association between habitat and gene frequency, although they were collected in such a way as to be capable of demonstrating such an association if it existed.

Acid Phosphatase↗
PubMed1976

Polymorphism and predictability at the alpha-glycerophosphate dehydrogenase locus in Colias butterflies: gradients in allele frequency within single populations.

Heterozygosity at the alpha-glycerophosphate dehydrogenase locus of five species of Colias butterflies is widespread in montane populations; alpine and lowland populations are not heterozygous. Within a single demographically characterized population of C. meadii where the population extends from alpine down into montane habitats, a marked cline in allele frequency is seen. Such within-population clines suggest the involvement of strong selection across the marked ecological interface. Thermal factors are the most likely causative agents, but associative overdominance is not excluded.

Acclimatization↗
PubMed1977

Determination of the bacteriostatic capacity of neutrophils and monocytes in mixed cell populations.

Cline [1, 2] described a method of determining the phagocytic and bacteriostatic activity of individual types of leukocytes within mixed cell populations. We tried to improve the applicability of this method for the investigation of clinical problems.--Bacteria in the log-phase of growth were incubated in test tubes with leukocytes separated from venous blood. After a short period of phagocytosis 3H-thymidine was added to label DNA-synthesizing organisms. Smears were prepared and processed by autoradiography. The labeling indices of extracellular bacteria and of those phagocytized by neutrophils and monocytes were determined microscopically. The intracellular inhibition of DNA-synthesis was taken as indicative of the bacteriostatic activity of the leukocytes. The proposed modification of Cline's assay is suited to investigate clinical problems of phagocyte dysfunction.

Autoradiography↗