Differential Gene Flow Research Articles

Genetic response to climatic change: insights from ancient DNA and phylochronology.

Understanding how climatic change impacts biological diversity is critical to conservation. Yet despite demonstrated effects of climatic perturbation on geographic ranges and population persistence, surprisingly little is known of the genetic response of species. Even less is known over ecologically long time scales pertinent to understanding the interplay between microevolution and environmental change. Here, we present a study of population variation by directly tracking genetic change and population size in two geographically widespread mammal species (Microtus montanus and Thomomys talpoides) during late-Holocene climatic change. We use ancient DNA to compare two independent estimates of population size (ecological and genetic) and corroborate our results with gene diversity and serial coalescent simulations. Our data and analyses indicate that, with population size decreasing at times of climatic change, some species will exhibit declining gene diversity as expected from simple population genetic models, whereas others will not. While our results could be consistent with selection, independent lines of evidence implicate differences in gene flow, which depends on the life history strategy of species.

Fine-scale population structure and dispersal in Biomphalaria glabrata, the intermediate snail host of Schistosoma mansoni, in Venezuela.

Biomphalaria glabrata is the main intermediate host of Schistosoma mansoni in America and one of the most intensely studied species of freshwater snails, yet very little is known about its population biology. Here, we used seven highly polymorphic microsatellite loci to analyse genetic diversity in the Valencia lake basin, which represents the core of the endemic area for schistosomiasis in Venezuela. Populations were sampled at short spatial scale (a few kilometres), both inside the lake and in ponds or rivers near the lake. Our results indicate that B. glabrata essentially cross-fertilizes, with little variation in selfing rates among populations. Our markers detected considerable genetic variation, with an average heterozygosity of 0.60. More diversity per population was found within than outside the lake, suggesting an influence of connectivity among populations on the levels of genetic diversity. A marked population structure was detected and lake populations were less structured than other populations. Most individuals were assigned to their population of origin using an assignment test. No strong demographic signal (e.g. bottleneck) was detected, though lake populations are likely to experience bottlenecks more frequently than the other populations analysed. Differences in gene flow therefore seem to play an important role in population differentiation and in the restoring of genetic diversity in demographically unstable populations.

DNA diversity in sex-linked and autosomal genes of the plant species Silene latifolia and Silene dioica.

The relatively recent origin of sex chromosomes in the plant genus Silene provides an opportunity to study the early stages of sex chromosome evolution and, potentially, to test between the different population genetic processes likely to operate in nonrecombining chromosomes such as Y chromosomes. We previously reported much lower nucleotide polymorphism in a Y-linked gene (SlY1) of the plant Silene latifolia than in the homologous X-linked gene (SlX1). Here, we report a more extensive study of nucleotide diversity in these sex-linked genes, including a larger S. latifolia sample and a sample from the closely related species Silene dioica, and we also study the diversity of an autosomal gene, CCLS37.1. We demonstrate that nucleotide diversity in the Y-linked genes of both S. latifolia and S. dioica is very low compared with that of the X-linked gene. However, the autosomal gene also has low DNA polymorphism, which may be due to a selective sweep. We use a single individual of the related hermaphrodite species Silene conica, as an outgroup to show that the low SlY1 diversity is not due to a lower mutation rate than that for the X-linked gene. We also investigate several other possibilities for the low SlY1 diversity, including differential gene flow between the two species for Y-linked, X-linked, and autosomal genes. The frequency spectrum of nucleotide polymorphism on the Y chromosome deviates significantly from that expected under a selective-sweep model. However, we detect population subdivision in both S. latifolia and S. dioica, so it is not simple to test for selective sweeps. We also discuss the possibility that Y-linked diversity is reduced due to highly variable male reproductive success, and we conclude that this explanation is unlikely.

Mississippians in motion? A population genetic analysis of interregional gene flow in West-Central Illinois.

Population genetic and biological distance studies of Late Woodland and Mississippian populations from west-central Illinois have provided insight into a number of prehistoric demographic processes at the regional level. However, a formal analysis of diachronic interregional gene flow has not been attempted within a population genetics framework. In this study, cranial measurements of 489 individuals from 13 skeletal samples across the central and lower Illinois valleys are analyzed to address two central issues. First, the potential impact of Cahokia's decline and associated demographic events on the population structure of west-central Illinois Mississippians is examined. Second, the Mississippian and Late Woodland interregional migration patterns are compared to determine if geographic and/or cultural boundaries affected local population structure. Following Relethford and Blangero ([1990] Hum Biol 62:5-25), R matrix methods are utilized to calculate observed and expected phenotypic variances, minimum genetic distances, and F(ST) values in order to detect patterns of differential external gene flow over time. The results indicate that Late Woodland peoples had a larger sphere of biological interaction than Mississippians. In the Mississippian period, culturally imposed barriers paralleled geographic boundaries between regions such that the geographic distribution of biological variation closely adheres to a classic isolation-by-distance model. Further, intraregional population movement was a more significant contributor to Mississippian population structure than interregional gene flow, even during periods of sociopolitical strife. Small-scale intraregional shuffling is consistent with other recent studies of prehistoric Mississippian biocultural and geographic landscapes in the southeast United States.

Maori origins, Y-chromosome haplotypes and implications for human history in the Pacific.

An assessment of 28 pertinent binary genetic markers on the non-recombining portion of the Y chromosome (NRY) in New Zealand Maori and other relevant populations has revealed a diverse genetic paternal heritage of extant Maori. A maximum parsimony phylogeny was constructed in which nine of the 25 possible binary haplotypes were observed. Although approximately 40% of the samples have haplotypes of unequivocal European origin, an equivalent number of samples have a single binary haplotype that is also observed in Indonesia and New Guinea, indicative of common indigenous Melanesian ancestry. The balance of the lineages has either typical East Asian signatures or alternative compositions consistent with their affinity to Melanesia or New Guinea. Molecular analysis of mtDNA variation confirms the presence of a single predominant characteristic Southeast Asian (9-bp deletion in the Region V) lineage. The Y-chromosome results support a pattern of complex interrelationships between Southeast Asia, Melanesia, and Polynesia, in contrast to mtDNA and linguistic data, which uphold a rapid and homogeneous Austronesian expansion. The Y-chromosome data highlight a distinctive gender-modulated pattern of differential gene flow in the history of Polynesia.

Autosomal, mtDNA, and Y-Chromosome Diversity in Amerinds: Pre- and Post-Columbian Patterns of Gene Flow in South America

To evaluate sex-specific differences in gene flow between Native American populations from South America and between those populations and recent immigrants to the New World, we examined the genetic diversity at uni- and biparental genetic markers of five Native American populations from Colombia and in published surveys from native South Americans. The Colombian populations were typed for five polymorphisms in mtDNA, five restriction sites in the beta-globin gene cluster, the DQA1 gene, and nine autosomal microsatellites. Elsewhere, we published results for seven Y-chromosome microsatellites in the same populations. Autosomal polymorphisms showed a mean G(ST) of 6.8%, in agreement with extensive classical marker studies of South American populations. MtDNA and Y-chromosome markers resulted in G(ST) values of 0.18 and 0.165, respectively. When only Y chromosomes of confirmed Amerind origin were used in the calculations (as defined by the presence of allele T at locus DYS199), G(ST) increased to 0.22. G(ST) values calculated from published data for other South American natives were 0.3 and 0.29 for mtDNA and Amerind Y chromosomes, respectively. The concordance of these estimates does not support an important difference in migration rates between the sexes throughout the history of South Amerinds. Admixture analysis of the Colombian populations suggests an asymmetric pattern of mating involving mostly immigrant men and native women.

A BIOGEOGRAPHIC GENETIC APPROACH FOR TESTING THE ROLE OF REINFORCEMENT: THE CASE OFDROSOPHILA PSEUDOOBSCURAANDD. PERSIMILIS

The role of reinforcement in speciation can be explained by two distinct models. In model I, two diverged populations hybridize and produce fertile hybrids that successfully backcross (hybridization with gene flow). In model II, two populations hybridize but succeeding backcrosses are unproductive (hybridization without gene flow). Using Drosophila persimilis and D. pseudoobscura, we have tested model I by comparing the extent of heterospecific introgression in sympatric versus allopatric populations. We show that certain expectations of this particular model of reinforcement, which is based on hybridization and gene flow between divergent populations after secondary contact, are not realized in these two species. The evidence consists of the similarity of genetic distances as well as proportions of unique/rare alleles between sympatric and allopatric heterospecific populations and a negative correlation between genetic distance and geographical distance between heterospecific populations, which suggests ecological differentiation. This approach in quantifying differential gene flow has important consequences to studies that compare sympatric and allopatric isolation using genetic distance. Following model I, one would expect a pattern of higher prezygotic isolation in sympatric species compared to allopatric species of the same genetic distance simply as a result of an underestimation of genetic distance due to introgression between sympatric populations. We suggest more parsimonious explanations such as reinforcement without genetic exchange (model II) and ecological differentiation, which require high levels of preexisting reproductive isolation between populations.

Genetic microstructure in two Spanish cat populations. I: genic diversity, gene flow and selection.

The genetic microstructure of two Spanish cat populations (in Barcelona and Alicante) was studied. These populations were in Hardy-Weinberg equilibrium at the locus O . There was significant genetic heterogeneity for most of the loci studied at the colony level, especially, and the subpopulation level in Barcelona, and at the subpopulation level in Alicante, although the amount of heterogeneity was relatively small compared with that found in other mammal species. Therefore, the major part of the gene diversity found was at the level of the small population structure (colonies). This agrees quite well with high theoretical gene flow estimates. The Lewontin-Krakauer test showed, in some cases, significant F tests, which appears to indicate the presence of several selective events on some of the loci studied (diversifying and/or unifying), although some other causes, such as differential gene flow, some different historical and demographic parameters at the time of the introduction of the different alleles within the cities studied, as well as different mutation rates of the loci analyzed, could produce significant Lewontin-Krakauer test values, as well.

Comparison of population structure in Ohio's late archaic and late prehistoric periods

Previous studies of population structure among prehistoric groups in the Ohio valley region have shown that hunting-gathering populations exhibited a different structure than horticultural populations. Among both Late Archaic hunter-gatherers and Late Prehistoric horticulturists, covariance structures for cranial metrics were found to be homogenous within the populations, but the Late Archaic subpopulations showed little differentiation while the Late Prehistoric subpopulations exhibited a marked differentiation. Biodistance based on cranial discrete trait frequency showed similar patterns, but in the Late Archaic discrete trait distance was associated significantly with the geographical distance separating populations. The present investigation is an extension of the previous studies increasing the Late Prehistoric sample (n = 8 samples and n = 341 individuals) and using the Harpending-Ward model, modified for use with multivariate quantitative data, to estimate the effects of differential gene flow and the amount of differentiation within populations. Results of the present analyses indicate that differentiation among subpopulations, measured by minimum F(ST), was greater in the Late Prehistoric compared to the Late Archaic period. However, for both periods the minimum F(ST) is comparable to values found for historic native populations of the northeast woodlands. Analysis of differential gene flow in the Late Archaic period indicates that geographically peripheral populations were affected more by external gene flow than more central populations. Late Prehistoric populations exhibit a very complex pattern of differential gene flow. We discuss the latter pattern in terms of proposed culture change in the Late Prehistoric period of Ohio.

A BIOGEOGRAPHIC GENETIC APPROACH FOR TESTING THE ROLE OF REINFORCEMENT: THE CASE OF DROSOPHILA PSEUDOOBSCURA AND D. PERSIMILIS

The role of reinforcement in speciation can be explained by two distinct models. In model I, two diverged populations hybridize and produce fertile hybrids that successfully backcross (hybridization with gene flow). In model II, two populations hybridize but succeeding backcrosses are unproductive (hybridization without gene flow). Using Drosophila persimilis and D. pseudoobscura, we have tested model I by comparing the extent of heterospecific introgression in sympatric versus allopatric populations. We show that certain expectations of this particular model of reinforcement, which is based on hybridization and gene flow between divergent populations after secondary contact, are not realized in these two species. The evidence consists of the similarity of genetic distances as well as proportions of unique/rare alleles between sympatric and allopatric heterospecific populations and a negative correlation between genetic distance and geographical distance between heterospecific populations, which suggests ecological differentiation. This approach in quantifying differential gene flow has important consequences to studies that compare sympatric and allopatric isolation using genetic distance. Following model I, one would expect a pattern of higher prezygotic isolation in sympatric species compared to allopatric species of the same genetic distance simply as a result of an underestimation of genetic distance due to introgression between sympatric populations. We suggest more parsimonious explanations such as reinforcement without genetic exchange (model II) and ecological differentiation, which require high levels of preexisting reproductive isolation between populations.Corresponding Editor: E. Zouros

Host resistance and pathogen virulence across a plant hybrid zone.

Hybridization between locally adapted plant populations has been postulated to have significant evolutionary consequences, and, in particular, may influence host-pathogen interactions with respect to resistance and virulence structure. This study investigated patterns of resistance and virulence in a hybrid zone between "bog" and "hill" ecotypes of the native Australian flax, Linum marginale, where the host is subject to attack by the rust pathogen, Melampsora lini. Analysis of the resistance structure of adjoining bog, hill and hybrid populations found that bog plants were generally susceptible to pathogen isolates taken from all these sites, but that hybrids exhibited resistance levels similar to the more resistant hill plants. Similarly, the virulence structure of rust isolates collected from the hybrid population was more similar to that of the hill isolates than the bog. Controlled crosses between bog and hill plants showed that crosses in one direction (bog females×hill males) were much more successful than the other. A multi-year reciprocal transplant study further indicated that bog plants had significantly higher survivorship than hill plants, regardless of site. It is suggested that likelihood of differential gene flow and survivorship for bog and hill plants may at least partially explain the maintenance of a relatively narrow hybrid zone.

Endophagous insects and structural niches on plants: ecology and evolutionary consequences

Summary1. The endophagous weevil Lixus elongatus was studied on two Carduus species in order to look for the impact of a structural gradient in host plant stem diameter on the life cycle and the genetic structure of this species.2. Body size of L. elongatus females was correlated positively with their fecundity and the stem diameter at the location of oviposition.3. Emerging individuals showed a significantly positive relationship of body size with the stem diameter at their pupation and emergence site. Mating behaviour was positively size‐assortative.4. Allozyme analyses indicated a gradient of genetic differentiation along body size classes and a decreasing heterozygosity with decreasing body size.5. The results led to the conclusion that a structural gradient in plants can promote body size variability in an endophagous herbivore through phenotypic constraints of the host plant and the herbivore. As size‐assortative mating translates this variability into differential gene flow between individuals of different body size, this could provide the raw material for speciation processes. Within a single host plant patch, however, further processes are necessary to split the existing genetic gradient into separate gene pools.

Ancient gene duplication and differential gene flow in plastid lineages: the GroEL/Cpn60 example.

Cryptomonads, small biflagellate algae, contain four different genomes. In addition to the nucleus, mitochondrion, and chloroplast is a fourth DNA-containing organelle the nucleomorph. Nucleomorphs result from the successive reduction of the nucleus of an engulfed phototrophic eukaryotic endosymbiont by a secondary eukaryotic host cell. By sequencing the chloroplast genome and the nucleomorph chromosomes, we identified a groEL homologue in the genome of the chloroplast and a related cpn60 in one of the nucleomorph chromosomes. The nucleomorph-encoded Cpn60 and the chloroplast-encoded GroEL correspond in each case to one of the two divergent GroEL homologues in the cyanobacterium Synechocystis sp. PCC6803. The coexistence of divergent groEL/cpn60 genes in different genomes in one cell offers insights into gene transfer from evolving chloroplasts to cell nuclei and convergent gene evolution in chlorophyll a/b versus chlorophyll a/c/phycobilin eukaryotic lineages.

Within‐population genetic structure in Quercus robur L. and Quercus petraea (Matt.) Liebl. assessed with isozymes and microsatellites

Molecular EcologyVolume 7, Issue 3 p. 317-328 Within-population genetic structure in Quercus robur L. and Quercus petraea (Matt.) Liebl. assessed with isozymes and microsatellites RÉJANE STREIFF, RÉJANE STREIFF INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this authorTHIERRY LABBE, THIERRY LABBE INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this authorROBERTO BACILIERI, ROBERTO BACILIERI INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this authorHERTA STEINKELLNER, HERTA STEINKELLNER Zentrum für Angewandte Genetik, Universität für Bodenkultur Wien, Muthgasse 18, A-1190 Vienna, AustriaSearch for more papers by this authorJOSEPH GLÖSSL, JOSEPH GLÖSSL Zentrum für Angewandte Genetik, Universität für Bodenkultur Wien, Muthgasse 18, A-1190 Vienna, AustriaSearch for more papers by this authorANTOINE KREMER, ANTOINE KREMER INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this author RÉJANE STREIFF, RÉJANE STREIFF INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this authorTHIERRY LABBE, THIERRY LABBE INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this authorROBERTO BACILIERI, ROBERTO BACILIERI INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this authorHERTA STEINKELLNER, HERTA STEINKELLNER Zentrum für Angewandte Genetik, Universität für Bodenkultur Wien, Muthgasse 18, A-1190 Vienna, AustriaSearch for more papers by this authorJOSEPH GLÖSSL, JOSEPH GLÖSSL Zentrum für Angewandte Genetik, Universität für Bodenkultur Wien, Muthgasse 18, A-1190 Vienna, AustriaSearch for more papers by this authorANTOINE KREMER, ANTOINE KREMER INRA, Station de Recherches Forestières, Laboratoire de Génétique et Amélioration des Arbres Forestiers, B. P. 45, F-33 611 Gazinet Cedex, France, ,Search for more papers by this author First published: 18 November 2003 https://doi.org/10.1046/j.1365-294X.1998.00360.xCitations: 246AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume7, Issue3March 1998Pages 317-328 RelatedInformation

The genetic structure of Beta vulgaris ssp. maritima (sea beet) populations. II. Differences in gene flow estimated from RFLP and isozyme loci are habitat-specific

In a previous paper, isolation by distance at RFLP loci was demonstrated in 10 populations of sea beet growing on the Dorset (U.K.) coast. In the same populations there was no evidence of isolation by distance at isozyme loci. Here, the data are reanalysed to reduce biases resulting from nonrandom mating within the populations; the contrast between RFLPs and isozymes remains very clear. Separate analysis of cliff-top populations shows strong isolation by distance at both RFLP and isozyme loci, whereas in populations on sea walls around the perimeter of Poole Harbour there is isolation by distance at RFLP loci but not isozyme loci. Thus, whatever the cause of the difference between RFLP and isozyme loci, it occurs in the harbour populations only. There was no evidence that founder effects are a significant source of variation between populations on the perimeter of the harbour. This is very different from a previous finding of strong founder effects between populations on Furzey Island (in Poole Harbour).

The genetic structure of Beta vulgaris ssp. maritima (sea beet) populations. II. Differences in gene flow estimated from RFLP and isozyme loci are habitat-specific

In a previous paper, isolation by distance at RFLP loci was demonstrated in 10 populations of sea beet growing on the Dorset (U.K.) coast. In the same populations there was no evidence of isolation by distance at isozyme loci. Here, the data are reanalysed to reduce biases resulting from nonrandom mating within the populations; the contrast between RFLPs and isozymes remains very clear. Separate analysis of cliff-top populations shows strong isolation by distance at both RFLP and isozyme loci, whereas in populations on sea walls around the perimeter of Poole Harbour there is isolation by distance at RFLP loci but not isozyme loci. Thus, whatever the cause of the difference between RFLP and isozyme loci, it occurs in the harbour populations only. There was no evidence that founder effects are a significant source of variation between populations on the perimeter of the harbour. This is very different from a previous finding of strong founder effects between populations on Furzey Island (in Poole Harbour).

MAINTENANCE OF ECOLOGICALLY SIGNIFICANT GENETIC VARIATION IN THE TIGER SWALLOWTAIL BUTTERFLY THROUGH DIFFERENTIAL SELECTION AND GENE FLOW.

Differential selection in a heterogeneous environment is thought to promote the maintenance of ecologically significant genetic variation. Variation is maintained when selection is counterbalanced by the homogenizing effects of gene flow and random mating. In this study, we examine the relative importance of differential selection and gene flow in maintaining genetic variation in Papilio glaucus. Differential selection on traits contributing to successful use of host plants (oviposition preference and larval performance) was assessed by comparing the responses of southern Ohio, north central Georgia, and southern Florida populations of P. glaucus to three hosts: Liriodendron tulipifera, Magnolia virginiana, and Prunus serotina. Gene flow among populations was estimated using allozyme frequencies from nine polymorphic loci. Significant genetic differentiation was observed among populations for both oviposition preference and larval performance. This differentiation was interpreted to be the result of selection acting on Florida P. glaucus for enhanced use of Magnolia, the prevalent host in Florida. In contrast, no evidence of population differentiation was revealed by allozyme frequencies. FST -values were very small and Nm, an estimate of the relative strengths of gene flow and genetic drift, was large, indicating that genetic exchange among P. glaucus populations is relatively unrestricted. The contrasting patterns of spatial differentiation for host-use traits and lack of differentiation for electrophoretically detectable variation implies that differential selection among populations will be counterbalanced by gene flow, thereby maintaining genetic variation for host-use traits.

Maintenance of Ecologically Significant Genetic Variation in the Tiger Swallowtail Butterfly Through Differential Selection and Gene Flow

Maintenance of Ecologically Significant Genetic Variation in the Tiger Swallowtail Butterfly Through Differential Selection and Gene Flow

Analysis of the evolution and genetic diversity within and between Balearic and Iberian cat populations.

A study of genic diversity and spatial autocorrelation of some cat populations has been carried out at the microgeographic (cities of Palma Majorca and Ibiza) and the macrogeographic (Balearic Islands and total Spain) levels. In both cases, the cat populations show high levels of gene flow (Nm) and few stochastic effects (e.g., genetic drift). Thus, cat populations are closer to the viewpoint of Mayr (1954)--that is, a species composed of large effective populations very near to panmixia--than to the hypothesis of demic structuration with very little gene flow between populations. The genetic differentiation between cat populations seems to be lower than that found in other vertebrate species. Nevertheless, I have found the existence of significant genetic heterogeneity at both the micro- and macrogeographical levels. At the microgeographical level, the differences in genetic heterogeneity at each of the loci studied within two populations could be caused by the introduction of the diverse mutant alleles into the analyzed populations at different historical times. At the macrogeographical level, the interaction of a strong differential gene flow caused by historical factors (and demographic changes) and, perhaps, natural selection for some loci is a possible explanation. The cat population data are in agreement with the hypothesis of Schwartz and Armitage (1980), who argued that social structures promote and augment gene flow between groups or populations of the same species. Humans seem to be the dominant element that explains the observed high rates of gene flow between cat populations.

Divergence in emergence time of host races due to differential gene flow

Differential gene flow between adjacent plant populations, induced by environmental influences on reproductive characters such as flowering time, may increase isolation between them (Stam, 1983). With the aid of a simulation model, an analogous process is demonstrated for populations of phytophagous insects. Allochronic isolation due to differences in host plant phenology can be accentuated in sympatry. Interpretations of divergence between host-associated insect populations should take account of the potential effects of differential gene flow before invoking explanations involving selection.