Amount Of Genetic Differentiation Research Articles

Influence of contrasting larval developmental types upon the population-genetic structure of cheilostome bryozoans

For many sedentary or sessile benthic marine invertebrates the planktonic duration of the larval stage is believed to be a key determinant of the magnitude of genetic differences between populations. An obvious dichotomy in dispersal potential exists within cheilostome bryozoans that develop from either (1) a cyphonautes larva that spends several weeks in the plankton or (2) a brooded coronate larva that settles soon after release from the adult colony. This study characterises the pattern of variation at allozyme loci among British populations of four species of bryozoan—two species with cyphonautes and two with coronate larvae. There is some variation in the estimates of genetic differentiation among similarly separated populations that may be a consequence of non-equilibrium genetic conditions arising from sporadic migration, possibly through dispersal by rafting on macroalgae by mature colonies. Despite this, however, both the level of genetic differentiation between populations and the pattern of migrant exchange correlate with the larval developmental mode. Bryozoan species that brood coronate larvae show higher levels of genetic heterogeneity between populations and significant isolation by distance genetic structure while, by contrast, distance has little or no effect upon the amount of genetic differentiation among populations of bryozoans with cyphonautes larvae. For cheilostome bryozoans, therefore, it appears that genetic differentiation between populations is directly associated with the type of larval development. These data are discussed also with respect to levels of gene diversity and the geological pattern of cheilostome bryozoan species diversity.

Large genetic distances among Aedes aegypti populations along the South Pacific coast of Mexico.

A population genetic analysis was conducted among 20 Aedes aegypti collections from 19 cities along the south Pacific coast in the Mexican states of Guerrero, Oaxaca, and Chiapas and in Coatepeque, Guatemala. Genetic variation was scored at 131 random amplified polymorphic DNA loci. The amount of genetic differentiation among collections was approximately 3 times as great as detected among collections in an earlier study in northeastern Mexico. Regression analysis of linear or road distances on linearized F(ST) indicated that collections are genetically isolated by distance. Cluster analysis failed to group collections in geographic proximity, and there was as much genetic variation among collections 60 km apart as there was among all collections (approximately 900-km range). The large genetic differentiation in southern Mexico reflects reduced gene flow among mosquitoes arising in a greater diversity of habitats and altitudes than exists among northeastern collections. It is likely that dispersal via human commerce in the northeast confounds patterns of natural gene flow.

HIERARCHICAL ANALYSIS OF GENETIC POPULATION STRUCTURE IN THE NOISY MINER USING DNA MICROSATELLITE MARKERS

Abstract The Noisy Miner (Manorina melanocephala) is a common, cooperatively breeding meliphagid of eastern and southeastern Australia. We used DNA microsatellites to examine the apportionment of genetic diversity in Noisy Miners at disparate geographic scales to generate baseline information about the population genetic structure of this species. We examined five loci for 79 individuals from four populations. We found small amounts of genetic differentiation between paired populations separated by 30–40 km, and more substantial and significant differentiation between populations separated by more than 1000 km. This result implies substantial gene flow on local scales but much less at regional levels, probably reflecting short dispersal distances and isolation by distance. Analisis Jerarquico de la Estructura Genetica Poblacional de Manorina melanocephala Utilizando Marcadores de ADN Microsatelital Resumen. Manorina melanocephala es un melifagido comun del sur-este de Australia que presenta cria cooperati...

Genetic diversity and differentiation in a southern beech subjected to introgressive hybridization.

Diversity and differentiation among 11 Argentine populations of the South American southern beech, Nothofagus nervosa (Phil.) Dimitri & Milano, were studied using eight isozyme gene markers. Genetic diversity, observed heterozygosity, mean number of alleles per locus, Gregorius' genetic distance, amount of genetic differentiation and mean level of differentiation among populations were estimated. Introgression of N. obliqua into the gene pool of N. nervosa was analysed using two species-specific isozyme gene markers (Adh-A and Pgi-B). As in most forest tree species, the main genetic variation was found within populations. Mean observed heterozygosity for the species was 17.3%, whilst mean level of genetic differentiation (deltage) was 4.6%. The most differentiated locus was Mdh-B with differences in 10% of the effective number of genes. From the analysis of the species distribution pattern it is suggested that genetic variation is geographically structured through the different lake watersheds along which the species is distributed. The occurrence of natural interspecific hybridization in some of the watersheds, together with the unidirectional gene flow along these watersheds sharpens this latitudinal structure. Different evolutionary stages in the introgressive hybridization process are apparently taking place in different lake watersheds.

Demic structure and its relation with the distribution of an adaptive trait in Danish flea beetles.

The flea beetle Phyllotreta nemorum is an oligophagous species using crucifers as host plants. In Denmark two populations have been found which use Barbarea vulgaris ssp. arcuata (G-type) as a host plant, whereas this plant is unsuitable for the survival of the majority of P. nemorum. In the locations in which these two populations occur, alternative host plants are also present. The plants occur in patches, some of which contain a mixture of host plants. In this study of allozyme variation, genetic differentiation between P. nemorum using different host plants in patches in the two different localities was studied hierarchically to assess substructuring of the populations. Evidence was found for low, but significant, amounts of genetic differentiation between (sub)populations using spatially separated plant patches at a distance of approximately 100 m to 1 km (theta = 0.009) and between localities approximately 44 km apart (theta = 0.026), and there was an association between genetic differentiation and geographical distance. No genetic differentiation was found between beetles from different host plants with overlapping local distributions. No evidence was thus found for sympatric host race formation. The geographical distribution of genes enabling P. nemorum to use B. vulgaris as a host plant (100% 'resistant' beetles in samples from B. vulgaris, but much fewer on patches containing only alternative host plants) contrasts with the relatively low amount of genetic differentiation at the neutral allozyme loci. This distribution of 'resistant' beetles (to B. vulgaris defence) is likely to be influenced by local differences in selection and asymmetric gene flow.

Effects of habitat fragmentation on population genetic structure in the white-footed mouse (Peromyscus leucopus)

Habitat fragmentation may have significant consequences for population genetic structure because geographic distance and physical barriers may impede gene flow. In this study, we investigated whether habitat fragmentation affects fine-scale genetic structure of populations of the white-footed mouse (Peromyscus leucopus). We studied 27 populations of P. leucopus, 17 in continuous forest and 10 in isolated woodlots. Populations were trapped in pairs that were either 500 or 2000 m apart. We estimated genetic variation at eight P. leucopus specific microsatellite DNA loci. We discovered significant genetic variation within all populations, but no significant differences in numbers of alleles or heterozygosity between populations. For given population pairs, we found significant genetic differentiation even at very short distances, based on multilocus FSTestimates. The amount of genetic differentiation between population pairs was similar in the two habitats. Distance had a marginal effect on genetic differentiation when comparing paired populations separated by 2000 m with those separated by 500 m. However, at a larger geographic scale, there was no evidence of isolation by distance. This study confirms that microsatellite-based studies have the potential to detect interpopulation differentiation at an extremely local scale, and suggests that habitat fragmentation has surprisingly few effects on P. leucopus genetic structure.

Microsatellite analysis reveals that domestic cat (Felis catus) and southern African wild cat (F. lybica) are genetically distinct

AbstractThe amount of genetic differentiation between the African wild cat (Felis lybica) and the domestic cat (F. catus) in southern Africa is not known, but there is concern that interbreeding between the two may have been sufficiently extensive to threaten the status of the wild cat as a genetically distinct population. Eight hypervariable microsatellite loci were therefore used to determine the genetic relationships within and among wild and domestic cat populations. Measures of genetic differentiation, including FST and RST, confirmed significant differentiation between the wild and domestic cat populations and no significant differentiation between two widely separate domestic cat populations. Our data indicate that the level of genetic introgression is lower than previously thought. This enhances the conservation status of the African wild cat and demonstrates the need for the implementation of feral cat control in and around game reserves and rural areas.

Genetic variation of five species of Trifolium L. from south-west Turkey

Following a legume collection mission to south-west Turkey in 1996, five species of Trifolium were analysed for genetic variation within and between species in eleven morphological and flowering characters. The five species included two outcrossing species, T. michelianum and T. resupinatum, and three inbreeding species, T. clypeatum, T. glomeratum and T. tomentosum. The genetic diversity found was related to climate and edaphic factors. All five species showed significant amounts of genetic differentiation between sites and the species could be separated morphologically by principal components analysis and cluster analysis. The most significant source of genetic variation was found to be related to geographical distribution with those species which were widely distributed across south-west Turkey exhibiting much greater amounts of genetic variation between sites, than those which had a narrow distribution. The breeding system was found to be less important, but only the morphology of the outbreeding species showed any environmental clines in relation to climate. A multiple regression analysis was computed to estimate the effect of growing season on the days to flowering of each of the species.

Breeding structure of Glossina pallidipes populations evaluated by mitochondrial variation

Mitochondrial DNA diversity was studied at four loci in six natural populations of the tsetse fly Glossina pallidipes from Zimbabwe, Mozambique, Kenya, and Ethiopia. Single-locus diversity varied from 0.39 at 12S to 0.65 at COII. A total of 32 haplotypes was found with a mean of 6.4 +/- 2.9 per locus. To study breeding structure, diversity at two loci, COII and 16S2, was evaluated in 18 populations sampled from an area of approximately 1,611,000 km2 and in three laboratory cultures. Twenty-six haplotypes were detected at the two loci and mean haplotype diversity over all natural populations was 0.63. A high degree of population subdivision was detected within and among the Ethiopian and Kenya populations. The Zimbabwe and Zambia populations showed much less variation and differentiation than the northern populations. A population in Mozambique showed high levels of haplotype variation and affinities closest to populations in eastern Kenya, some 1700 km to the north. Analysis of variance of haplotype frequencies showed that 51.5% of the total lay within populations, 13% among populations within five nested groups, and 35.5% among the five groups. Wright's FST was 0.485, Nei's GST was 0.33, and Weir and Cunningham's theta = 0.45. Ecological data show that G. pallidipes is highly vagile. The large amount of genetic differentiation may be explained by genetic drift that occurred in scattered, relict populations during the rinderpest panzootic of the late 19th and early 20th centuries.

Host use evolution in Chrysochus milkweed beetles: evidence from behaviour, population genetics and phylogeny

In two sister species of leaf beetles with overlapping host associations, Chrysochus auratus and C. cobaltinus, we established diet breadth and food preference of local populations for evaluation together with genetic differentiation between populations. While C. auratus turned out to be monophagous on the same plant wherever we collected the beetles, the studied populations of C. cobaltinus fed on three different plant species in the field. Plant preference and ranking of the potential host plants significantly differed between these populations. The amount of genetic differentiation between populations was measured by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay of a 1300 bp mitochondrial DNA (mtDNA) sequence. In addition, the dominant genotypes of all populations were sequenced. No genetic differentiation between the populations of C. auratus could be detected in the RFLP assay and sequence divergence was low (= 0.3%). In C. cobaltinus, on the other hand, genetic differentiation between populations was high, revealing a lack of gene flow over a much smaller scale and a maximum of 1.3% sequence divergence. C. cobaltinus thereby has the prerequisites for host race formation on different plants from the original host spectrum. Our sequence-based phylogeny estimate allows us to reconstruct historical diet evolution in Chrysochus. Starting from an original association with Asclepiadaceae, the common ancestor of C. auratus and C. cobaltinus included Apocynaceae in its diet. The strict specialization on Apocynum and the loss of acceptance of Asclepiadaceae observed in C. auratus could have resulted from a process similar to that displayed by C. cobaltinus populations.

Cryptic radiation in erpobdellid leeches in xeric landscapes: a molecular analysis of population differentiation

Despite apparent long-term geographic isolation, many invertebrates demonstrate little apparent morphological differentiation. To examine underlying genetic differentiation, eight erpobdellid leech populations from widely dispersed northern Arizona aquatic ecosystems were examined by means of amplified fragment length polymorphism genetic markers. These populations were primarily Erpobdella punctata, though two populations, Motobdella montezuma and Motobdella sedonensis, have been described as novel taxa. Data from 137 polymorphic loci were used to estimate genetic heterogeneity (θ), migration rates (Nm), and genetic similarities (Dice's method) among these populations. Analysis of molecular variance and cluster analysis (unweighted pair-group method) were used to show population structure and to partition the genetic variance. Our analysis indicates that northern Arizona leech populations are genetically isolated (θ = 0.72, Nm = 0.09), with significant (p < 0.01) differentiation among populations. In addition, no relationship was found between genetic and geographic distances (r = 0.19, p = 0.22), which is consistent with long-term isolation even when populations are in close proximity. The large amount of genetic differentiation reveals levels of diversity and complexity not apparent from morphological comparisons alone and suggests that erpobdellid leeches in the arid landscape of the southwestern U.S.A. are in fact evolving independently from one another.

Genetic differentiation among laboratory populations of Hyalella azteca: Implications for toxicology

AbstractHyalella azteca of different origins are maintained in many laboratories and are extensively used in toxicological bioassays. Quality assurance of interlaboratory toxicity data can only be made when the amount of genetic differentiation among laboratory populations is known. We assayed genetic variability at 16 enzymatic loci in H. azteca stocks from six laboratories (2 U.S. Environmental Protection Agency [USEPA], 1 U.S. Fish and Wildlife Service [USFWS], University of Mississippi, Environment Canada, Burlington, ON, Canada, and New York Department of Environmental Conservation), as well as an additional species, Hyalella montezuma (used as an outgroup). Three divergent groups were identified in laboratory stocks of H. azteca based on both Nei's genetic identity and modified Rogers' genetic distance. These three groups were differentiated genetically at a level characteristic of distinct species (Nei's I = 0.26–0.69) based on the comparison between H. azteca and H. montezuma. The high level of genetic differentiation among populations indicated that the Burlington and New York populations were distinct species of Hyalella. In order to enhance interlaboratory toxicity test comparisons, we recommend using genetically characterized populations of H. azteca.

Genetic structure of populations of beech(Fagus sylvaticaL.) in Denmark

The genetic structure in Danish indigenous and introduced provenances of beech (Fagus sylvatica L.) is described. Ten stands are analysed based on variation revealed by seven enzyme systems. The present study reveals significant allele frequency differences between populations with a small absolute amount of genetic differentiation, with no pattern related to geographic distance. The genetic differentiation between indigenous populations measured by Wright's F ST‐statistic does not deviate significantly from zero, and only 2.9% of the total genetic variation in the foreign populations was due to interpopulation differences, The allele frequencies in relatively small and isolated populations do not differ from the frequencies found in larger areas with beech forest. The low genetic differentiation of isozyme level between indigenous and foreign populations was opposed by significant differences in foliation performance measured on three pairs of neighbouring stands. Foliation performance in adjacent stands...

Electrophoretic Characterization of Odd-Year Pink Salmon (Oncorhynchus gorbuscha) Populations from the Pacific Coast of Russia, and Comparison with Selected North American Populations

We collected and electrophoretically analyzed a total of 558 fish from eight locations along the Pacific Coast of Russia. We successfully screened 44 enzyme-coding loci: 14 loci were polymorphic at the 0.95 level in at least one collection, an additional eight were polymorphic at the 0.99 level but not at the 0.95 level, and the remaining 22 were either monomorphic or exhibited only very rare variation in these collections. Contingency χ2 tests using the 23 most variable loci revealed significant heterogeneity among all eight collections (p = 0.028) but little or no significant heterogeneity among collections within areas (northeastern Kamchatka peninsula, p = 0.180; southwestern Kamchatka, p = 0.533; and mainland adjacent to the northwestern Sea of Okhotsk, p = 0.071). Multidimensional scaling and minimum spanning tree analyses using genetic distances among collections indicated that geographic proximity of spawning sites was not associated with genetic similarity. The eight odd-year pink salmon (Oncorhynchus gorbuscha) collections from Russia were compared with 16 collections from North America (southeastern Alaska, British Columbia, and Washington) using data for 33 loci. The Russian populations differed from the North American populations in their patterns of allelic variation at many loci. The amount of genetic differentiation among populations from different rivers in Russia was comparable to that seen within similar-sized areas in North America.

Transferrin variation and evolution of Canadian barren-ground caribou

Blood samples were obtained from 95 barren-ground caribou (Rangifer tarandus groenlandicus) of the Beverly herd in Northwest Territories, Canada. Polyacrylamid gel electrophoresis was used to score for genetic variation in the locus coding for transferrin. The pattern of allele frequency distribution are compared with previously reported values of Eurasian tundra reindeer (R.t. tarandus), Alaska caribou (R.t. granti), Peary caribou (R.t. pearyi), and Svalbard reindeer (R.t. platyrhynchus). In the Beverly herd a total of 21 different transferrin alleles were detected. The amount of genetic variation was higher in the Canadian barren-ground caribou than what has been detected in other subspecies of reindeer/caribou. Highly gene-tical differences in the allele frequencies were detected between the Canadian barren-ground caribou and the other subspecies. The genetic identity analyses indicates approximately the same amount of genetic differentiation when the Canadian barren-ground caribou are compared with Alaska caribou as with the Peary caribou. The allele frequency pattern could be explained by a possible origin of the Canadian barren-ground caribou from an ancestral population which was genetical influenced by animals surviving the We-ichselian glaciation in refugia both in high Arctic, in Beringia, and south of the ice sheet.

Molecular Genetics of Populations of Intracellular Bacteria: The Spotted Fever Group Rickettsiae

The population structure of tick-borne rickettsiae show the following characteristics: (1) the amount of genetic differentiation between strains within subpopulations is very small. (2) The evolution of the subpopulations does not fit into models based on either host or geographic similarities, suggesting the need for more information on the frequency of vertical versus horizontal transmission of strains between hosts. (3) The species are highly clonal, with little evidence of genetic exchange between populations. (4) The dominant class of genetic change is single-nucleotide point mutation. No evidence for major rearrangements was observed. (5) Differentiation between species of the spotted fever group is equivalent to that seen between local strains of E. coli.

Blood-protein polymorphism in the Japanese cats.

Blood samples were collected from alley or feral populations of cats in four prefectures of Japan, and genetic variation at 31 blood-protein loci were examined by starch-gel electrophoreses. The proportion of polymorphic loci and the average heterozygosity were estimated as 0.2580-0.3548 (mean: 0.2903) and 0.0741-0.0917 (mean: 0.0793), respectively, Whereas these values are on a standard level of the genetic variability of domesticated animals, they are conspicuously higher compared with those of such wild mammals as Japanese macaque and Japanese serow. Amount of genetic differentiation among the prefectural populations was evaluated with the FST and GST statistics as 0.0075 and 0.0112, respectively. These values are more than one order lower than those among local subpopulations of the Japanese macaques, suggesting that the gene constitution of Japanese cats are fairly homogeneous over the country.

Electrophoretic analysis of a chromosomal hybrid zone in the grasshopper Podisma pedestris

We have made an extensive allozyme survey of 21 enzyme and protein loci in populations of the alpine grasshopper Podisma pedestris. This species occurs in two races, differing by a chromosomal fusion which separates the ancestral XO/XX race from a derived neo-XY race. These races also differ in DNA content, and hybrids between them have reduced viability. Electrophoresis reveals that the amount of genetic differentiation between these races is no greater than the variation among populations within each race. Both larger-scale surveys and a detailed survey of an area where the races hybridize, show that the chromosomal change is not correlated with gene frequency changes at any of the 21 loci studied. These findings are consistent with recently developed theory concerning the strength of the barrier to gene flow posed by a hybrid zone with characteristics such as those measured experimentally in Podisma. It is argued that hybrid zones in other species which involve allozymic differences do so because of stronger selection against hybrids rather than through mating isolation.

Electrophoretically estimated genetic distance and divergence time between chimpanzee and man

Amount of genetic differentiation between chimpanzee and man was estimated from the result of comparative electrophoretic screening of blood protein variations at 32 independent genetic loci. TheNei's genetic distance (D) was calculated as 0.4514, and from this value the divergence time between the two species was estimated as 2.26 million years; considering the variation among amino-acid substitution rate in different proteins, the corrected figures were given as genetic distance of 0.5706 and divergence time of 2.85 million years. This genetic difference is considered too small the two species to be allocated in different families, in accordance with the results of the similar kind of analyses byKing andWilson (1975) and Bruce andAyala (1979). Discussions were made for a discrepancy between the divergence times estimated by using and not by using the splitting time recognized by paleoprimatologists as a reference, and for the difference in the estimations made in different laboratories.

Geographic and Temporal Patterns of Genetic Variation of Aedes Aegypti in New Orleans

Populations of Aedes aegypti were collected in 1976 and 1979 from a number of different areas of New Orleans and analyzed for genetic variation of 12 isozyme loci. Although six loci were polymorphic, the majority of loci showed no significant genetic differentiation over time or between regions. The greatest amount of genetic differentiation was found between populations bordering the Mississippi River and the two inland areas, Mid-City and Mount Olivet. The low amount of genetic heterogeneity among areas is consistent with the known rapid spread and migration of A. aegypti in recent years. New Orleans A. aegypti are genetically most closely related to populations from Florida, and are less related to collections from several Caribbean islands with a recent history of epidemic dengue fever. Knowledge of the structure of A. aegypti populations in New Orleans, as well as their genetic relatedness to those of other regions, may provide important information concerning the potential of these populations as vectors of epidemic dengue fever.