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PubMed2005

Effective size of a fluctuating age-structured population.

Previous theories on the effective size of age-structured populations assumed a constant environment and, usually, a constant population size and age structure. We derive formulas for the variance effective size of populations subject to fluctuations in age structure and total population size produced by a combination of demographic and environmental stochasticity. Haploid and monoecious or dioecious diploid populations are analyzed. Recent results from stochastic demography are employed to derive a two-dimensional diffusion approximation for the joint dynamics of the total population size, N, and the frequency of a selectively neutral allele, p. The infinitesimal variance for p, multiplied by the generation time, yields an expression for the effective population size per generation. This depends on the current value of N, the generation time, demographic stochasticity, and genetic stochasticity due to Mendelian segregation, but is independent of environmental stochasticity. A formula for the effective population size over longer time intervals incorporates deterministic growth and environmental stochasticity to account for changes in N.

Age Factors↗
PubMed1998

Morphometric dimensions of metacarpal bones in the population structure analysis (island of Krk, Croatia).

The population structure analysis by means of the osteometric dimensions of metacarpal bones in the population groups of the northern Adriatic island of Krk, Croatia was performed. The sample consisted of randomly sampled adult islanders (94 males and 79 females) aged from 18 to 85 years from six villages of the island of Krk. "Biological distances" were estimated by the Mahalanobis D2 analysis for bone length (L), total diaphysis width (T) and medullary canal width (M) dimensions of the second left metacarpal bone. Analysis of the osteometric dimensions of metacarpal bones as a measure of biological distance between population groups of the island of Krk indicated bio-cultural and socio-cultural events, rather than geographical distances, to be the primary determinants of anthropogenetic structure of today's population groups of the island.

Adolescent↗
PubMed1982

Genetic population structure in polygynous formica ants.

Genetic population structures, both mating and interaction structures, were investigated in three polygynous Formica ants by examining how genotype frequencies are distributed among the nests in their populations. The study is based on electrophoretically analysed enzyme polymorphisms. The patterns of genotypic variation among single-nest workers suggest that polygyny is functional in all the three species. The observed genotype frequencies indicate outbreeding within the study areas, and no spatial microdifferentiation in gene frequencies is detected. The coexistent gynes in nests of both F. transkaucasica and F. polyctena are genetically related to each other, and the same holds for worker nest mates. These results support the hypothesis that polygyny is favoured by kin selection. The lack of genetic relatedness among gyne nest mates in the highly polygynous F. aquilonia suggests that additional factors, such as mutualism or parental parasitism, are probably involved in the evolution of polygyny.

Animals↗
PubMed2002

Population structure of a parasitic plant and its perennial host.

Characterization of host and parasite population genetic structure and estimation of gene flow among populations are essential for the understanding of parasite local adaptation and coevolutionary interactions between hosts and parasites. We examined two aspects of population structure in a parasitic plant, the greater dodder (Cuscuta europaea) and its host plant, the stinging nettle (Urtica dioica), using allozyme data from 12 host and eight parasite populations. First, we examined whether hosts exposed to parasitism in the past contain higher levels of genetic variation. Second, we examined whether host and parasite populations differ in terms of population structure and if their population structures are correlated. There was no evidence that host populations differed in terms of gene diversity or heterozygosity according to their history of parasitism. Host populations were genetically more differentiated (F(ST) = 0.032) than parasite populations (F(ST) = 0.009). Based on these F(ST) values, gene flow was high for both host and parasite. Such high levels of gene flow could counteract selection for local adaptation of the parasite. We found no significant correlation between geographic and genetic distance (estimated as pairwise F(ST)), either for the host or for the parasite. Furthermore, host and parasite genetic distance matrices were uncorrelated, suggesting that sites with genetically similar host populations are unlikely to have genetically similar parasite populations.

Alleles↗
PubMed2005

New method for surname studies of ancient patrilineal population structures, and possible application to improvement of Y-chromosome sampling.

Several studies showed that surnames are good markers to infer patrilineal genetic structures of populations, both on regional and microregional scales. As a case study, the spatial patterns of the 9,929 most common surnames of the Netherlands were analyzed by a clustering method called self-organizing maps (SOMs). The resulting clusters grouped surnames with a similar geographic distribution and origin. The analysis was shown to be in agreement with already known features of Dutch surnames, such as 1) the geographic distribution of some well-known locative suffixes, 2) historical census data, 3) the distribution of foreign surnames, and 4) polyphyletic surnames. Thus, these results validate the SOM clustering of surnames, and allow for the generalization of the technique. This method can be applied as a new strategy for a better Y-chromosome sampling design in retrospective population genetics studies, since the idenfication of surnames with a defined geographic origin enables the selection of the living descendants of those families settled, centuries ago, in a given area. In other words, it becomes possible to virtually sample the population as it was when surnames started to be in use. We show that, in a given location, the descendants of those individuals who inhabited the area at the time of origin of surnames can be as low as approximately 20%. This finding suggests 1) the major role played by recent migrations that are likely to have distorted or even defaced ancient genetic patterns, and 2) that standard-designed samplings can hardly portray a reliable picture of the ancient Y-chromosome variability of European populations.

Chromosomes, Human, Y↗
PubMed1980

Necator americanus: population structure, distribution, and fluctuations in population densities of infective larvae in contaminated farmlands.

Observations have been made over a 15-month period on the frequency distribution of human faecal deposits and infective larvae of Necator americanus in a hookworm endemic area. The agestructure of infective larvae in a field population and their vertical distribution in soils were determined. These studies were undertaken to examine the hypothesis that hookworm transmission in the tropics is discontinuous and limited mainly to the rainy season. The distribution of larvae was found to be overdispersed statistically and in general much greater numbers of L3s were recovered during the rainy season. The degree of overdispersion was also reduced during this season, and there was a tendency for larvae to be confined to the surface/topsoil. The implications of these findings have been discussed in relation to human hookworm parasitism in endemic areas of the tropics.

Animals↗
PubMed2003

Geographical variation, population structure and gene flow between populations of Chrysophtharta agricola (Coleoptera: Chrysomelidae), a pest of Australian eucalypt plantations.

Chrysophtharta agricola (Chapuis) is a pest of commercial eucalypt plantations in Tasmania and Victoria. Vagility of pest populations may result in difficulty predicting temporal and spatial pest outbreaks, and influence genetic resistance to chemical control. Gene flow in this pest species was estimated to assess predictability of attack, the potential efficacy of natural enemies, and the likelihood of resistance build-up. Ten geographic populations of C. agricola (six from Tasmania, one from the Australian Capital Territory, one from New South Wales and two from Victoria) were examined for genetic variation and gene flow using cellulose acetate allozyme electrophoresis. Six enzyme systems (PGI, PGD, PGM, IDH, HEX and MPI) were consistently polymorphic and scorable and were used to quantify estimated gene flow between populations. FST values and analysis of molecular variance indicated that gene flow was restricted between populations. Chrysophtharta agricola exhibited high levels of heterozygosity, probably because of high allelic diversity, and because all loci examined were polymorphic. The southern-most population was the most genetically different to other Tasmanian populations, and may also have been the most recently colonized. Limited gene flow implies that outbreaks of C. agricola should be spatially predictable and populations susceptible to control by natural enemies. Our results also imply that genetic resistance to chemical control may occur under frequent application of insecticide. However, testing population movement between plantations and native forest also needs to be conducted to assess gene flow between forest types.

Animals↗
PubMed1988

[Comparative studies of the population structure of a Kurd village population in Southeast Turkey. I. Morphologic regional comparison].

The paper is dealing with an anthropological investigation of a Kurdish village population from southern Turkey. We especially attached importance on the complete registration of all inhabitants to get a reliable sample for regional comparison of morphological features. Anthropological data of other Kurdish population groups are used for univariate and multivariate analysis. The resulting clusters are discussed beside the question of representation under the standpoint of regional and cultural origin of the samples.

Anthropometry↗
PubMed1988

[Comparative studies of the population structure of a Kurd village population of Southeast Turkey. II. Morphologic differentiation within the population].

A small scale village society from southern Turkey has been investigated by demographic, social and anthropological criteria. An internal differentiation of the population on the basis of demographic and social data could be verified for morphological features, too. This is shown clearly by a differentiation of the population into two family complexes. The consequences for the interpretation of metrical random sample surveys in typological investigations are discussed.

Adult↗
PubMed2001

Population structure inhibits evolutionary diversification under competition for resources.

A model is presented that explores how population structure affects the evolutionary outcome of ecological competition for resources. The model assumes that competition for resources occurs within groups of a finite number of individuals (interaction groups), and that limited dispersal of individuals between groups (according to Wright's island model of population structure) results in genetic structuring of the population. It is found that both finite-sized interaction groups and limited dispersal can have substantial effects on the evolution of resource exploitation strategies as compared to models with a single, infinitely large, well-mixed interaction group. Both effects, in general, tend to select for less aggressive competitive strategies. Moreover, both effects also tend to reduce the likelihood of the evolutionary diversification of resource exploitation strategies that often occurs in models of resource competition with infinite populations. The results are discussed in the context of theories of the evolutionary diversification of resource exploitation strategies and speciation.

Biological Evolution↗
PubMed2026

Assessment of Genetic Diversity and Population Structure on Azadirachta indica A. Juss. in an Urban Metropolitan: Ahmedabad, India.

Azadirachta indica (A. indica) A. Juss., commonly known as Neem, is a valuable multipurpose tree with profound medicinal properties and socioeconomic importance, widely recognized since ancient Ayurvedic times. Despite its prominence, knowledge about its genetic diversity within the metropolitan area of Ahmedabad is limited. This study marks the first in-depth exploration of the genetic diversity and population structure of A. indica in Ahmedabad. The authenticity of the species was validated through DNA barcoding, and a Geographical Information System (GIS) was used to collect the samples. A total of 35 A. indica accessions were analyzed using five Inter Simple Sequence Repeat (ISSR) primers. Genetic diversity and population structure were evaluated using Inter Simple Sequence Repeat (ISSR) markers through polymorphism assessment, clustering, ordination, and Bayesian population structure analyses. ISSRs revealed a high level of polymorphism (75.66%), indicating substantial genetic variability among accessions. An analysis of genetic diversity indices revealed low to moderate diversity (Hs = 0.14, Ht = 0.217, I = 0.217). Analysis of Molecular Variance (AMOVA) analysis depicted 81% variation within the population and 19% among the population. Low to moderate genetic differentiation (Gst = 0.319) and moderate gene flow (Nm = 1.06) indicated that urban development has not hindered gene flow among populations. Mantel's test revealed a weak but significant correlation between genetic and geographic distances, suggesting limited isolation by distance. The estimated ΔK using STRUCTURE exhibited two subpopulations, representing two gene pools for A. indica accessions (K = 2). Collectively, these patterns indicate that urbanization has not severely disrupted genetic connectivity in A. indica, reflecting its resilience and adaptive potential in a metropolitan environment. These findings provide pivotal knowledge for further understanding the genetic diversity and population structure of A. indica in one of the fastest-growing cities in India, which can be utilized for new breeding programmes, sustainable development and future conservation strategies around the globe.

India↗
PubMed2003

Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes.

We investigated genetic differentiation among populations of the clonal grass Elymus athericus, a common salt-marsh species occurring along the Wadden Sea coast of Europe. While E. athericus traditionally occurs in the high salt marsh, it recently also invaded lower parts of the marsh. In one of the first analyses of the genetic population structure in salt-marsh species, we were interested in population differentiation through isolation-by-distance, and among strongly divergent habitats (low and high marsh) in this wind- and water-dispersed species. High and low marsh habitats were sampled at six sites throughout the Wadden Sea. Based on reciprocal transplantation experiments conducted earlier revealing lower survival of foreign genotypes we predicted reduced gene flow among habitats. Accordingly, an analysis with polymorphic cross-species microsatellite primers revealed significant genetic differentiation between high and low marsh habitats already on a very small scale (< 100 m), while isolation-by-distance was present only on larger scales (60-443 km). In an analysis of molecular variance we found that 14% of the genetic variance could be explained by the differentiation between habitats, as compared to only 8.9% to geographical (isolation-by-distance) effects among six sites 2.5-443 km distant from each other. This suggests that markedly different selection regimes between these habitats, in particular intraspecific competition and herbivory, result in habitat adaptation and restricted gene flow over distances as small as 80 m. Hence, the genetic population structure of plant species can only be understood when considering geographical and selection-mediated restrictions to gene flow simultaneously.

Ecosystem↗
PubMed2000

Ecological determinants and temporal stability of the within-river population structure in Atlantic salmon (Salmo salar L.).

A gene diversity analysis was performed using microsatellite loci in order to (i) describe the extent and pattern of population structure in Atlantic salmon (Salmo salar L.) within a river system; (ii) establish the importance of quantifying the signal:noise ratio in accurately estimating population structure; and (iii) assess the potential usefulness of two evolutionary models in explaining within-river population structure from the ecological and habitat characteristics of Atlantic salmon. We found weak, yet highly significant microscale spatial patterning after accounting for variance among temporal replicates within sites. Lower genetic distances were observed among temporal samples at four sampling sites whereas no evidence for temporal stability was observed at the other three locations. The component of genetic variance attributable to either temporal instability and/or random sampling errors was almost three times more important than the pure spatial component. This indicates that not considering signal:noise ratio may lead to an important overestimation of genetic substructuring in situations of weak genetic differentiation. This study also illustrates the usefulness of the member-vagrant hypothesis to generate a priori predictions regarding the number of subpopulations that should compose a species, given its life-history characteristics and habitat structure. On the other hand, a metapopulation model appears better suited to explain the extent of genetic divergence among subpopulations, as well as its temporal persistence, given the reality of habitat patchiness and environment instability. We thus conclude that the combined use of both models may offer a promising avenue for studies aiming to understand the dynamics of genetic structure of species found in unstable environments.

Animals↗
PubMed1999

Host and parasite population structure in a natural plant-pathogen system

We investigated the genetic population structure in a metapopulation of the plant Silene latifolia (Caryophyllaceae) and its fungal pathogen Microbotryum violaceum (Ustilaginales), a pollinator-borne disease. Population structure of the host plant was estimated using allozyme markers and that of the fungus by microsatellites. Both host and parasite showed significant differentiation, but parasite populations were 12 times more strongly differentiated than those of the hosts. We found significant isolation by distance for host populations but not for parasite populations. Higher population differentiation for the parasite may result from small effective population size, high selfing rates, or low migration rate. In this system, hosts are obligate outcrossers and they migrate by seeds and pollen, whereas parasites can self-fertilize and migrate only on pollinating insects. We discuss the effect of limited gene flow in this parasite on its coevolutionary interaction with its host, and its potential for local adaptation on sympatric host populations.

Journal Article↗
PubMed2003

The influence of demography, population structure and selection on molecular diversity in the selfing freshwater snail Biomphalaria pfeifferi.

Several forces may affect the distribution of genetic diversity in natural populations when compared to what is expected in a random-mating, constant size population of neutral genes. One solution for unravelling their respective influence is to study several genes at once in order to better reflect the true genealogy. Here we reconstruct the evolutionary history of the freshwater snail Biomphalaria pfeifferi over its entire distribution, using eight African populations, and three congeneric species as outgroups. A phylogenetic analysis was conducted using amplified fragment length polymorphism markers, and sequences at eight nuclear non-coding loci and one mitochondrial gene were used to analyse population structure. The geographic distribution of variation suggests greater affinities within than among regions. The pattern of variability at both the nuclear and mitochondrial DNA (mtDNA) loci is consistent with a bottleneck, although population structure may also partly explain our results. Our results are also indicative of the role of selection, whether positive or purifying, in the mtDNA. This highlights the fact that the interfering influences of population structure, demography and selection on molecular variation are not easily distinguished.

Animals↗
PubMed1989

[Estimation of the population structure of the Etimesgut Health District in the year 2025].

The author forecasts the population of the Etimesgut Health District in Turkey for the year 2025 under certain assumptions. "According to these basic assumptions [the] crude birth rate will decrease to 14 per thousand and [the] crude death rate will increase to 9.47 per thousand within 35 years.... According to these results, the population pyramids of the Etimesgut Health District were drawn for different years. As it will be seen, the population structure will not be like today's developed countries' population structure until the year 2070." (SUMMARY IN ENG)

Asia↗
PubMed2006

Evidence of microsatellite hitch-hiking selection in Atlantic cod (Gadus morhua L.): implications for inferring population structure in nonmodel organisms.

Microsatellites have gained wide application for elucidating population structure in nonmodel organisms. Since they are generally noncoding, neutrality is assumed but rarely tested. In Atlantic cod (Gadus morhua L.), microsatellite studies have revealed highly heterogeneous estimates of genetic differentiation among loci. In particular one locus, Gmo 132, has demonstrated elevated genetic differentiation. We investigated possible hitch-hiking selection at this and other microsatellite loci in Atlantic cod. We employed 11 loci for analysing samples from the Baltic Sea, North Sea, Barents Sea and Newfoundland covering a large part of the species' distributional range. The 'classical' Lewontin-Krakauer test for selection based on variance in estimates of F(ST) and (standardized genetic differentiation) revealed only one significant pairwise test (North Sea-Barents Sea), and the source of the elevated variance could not be ascribed exclusively to Gmo 132. In contrast, different variants of the recently developed ln Rtheta test for selective sweeps at microsatellite loci revealed a high number of significant outcomes of pair-wise tests for Gmo 132. Further, the presence of selection was indicated in at least one other locus. The results suggest that many previous estimates of genetic differentiation in cod based on microsatellites are inflated, and in some cases relationships among populations are obscured by one or more loci being the subject to hitch-hiking selection. Likewise, temporal estimates of effective population sizes in Atlantic cod may be flawed. We recommend, generally, to use a higher number of microsatellite loci to elucidate population structure in marine fishes and other nonmodel species to allow for identification of outlier loci that are subject to selection.

Alleles↗
PubMed2002

Mitochondrial DNA diversity, population structure, and gender association in the gynodioecious plant Silene vulgaris.

A highly variable mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) locus is used to assess the population structure of mitochondrial genomes in the gynodioecious plant Silene vulgaris at two spatial scales. Thirteen mtDNA haplotypes were identified within 250 individuals from 18 populations in a 20-km diameter region of western Virginia. The population structure of these mtDNA haplotypes was estimated as thetaST = 0.574 (+/- 0.066 SE) and, surprisingly, genetic differentiation among populations was negatively correlated with geographic distance (Mantel r = -0.246, P < 0.002). Additionally, mtDNA haplotypes were spatially clumped at the scale of meters within one population. Gender in S. vulgaris is determined by an interaction between autosomal male fertility restorers and cytoplasmic male sterility (CMS) factors, and seed fitness is affected by an interaction between gender and population sex ratio; thus, selection acting on gender could influence the distribution of mtDNA RFLP haplotypes. The sex ratio (females:hermaphrodites) varied among mtDNA haplotypes across the entire metapopulation, possibly because the haplotypes were in linkage disequilibrium with different CMS factors. The gender associated with some of the most common haplotypes varied among populations, suggesting that there is also population structure in male fertility restorer genes. In comparison with reports of mtDNA variation from other published studies, we found that S. vulgaris exhibits a large number of mtDNA haplotypes relative to that observed in other species.

DNA, Mitochondrial↗