Spatial distribution of cpDNA and mtDNA haplotypes in a hybrid zone betweenPinus pumila andP. parviflora var.pentaphylla (Pinaceae)

Pinus species exhibit paternal chloroplast inheritance and maternal mitochondrial inheritance. This independent inheritance of two cytoplasmic genomes provides an exceptional environment for discriminating female (seeds) and male (pollen) components of gene flow across hybridizing species. We obtained mitochondrial genetic markers diagnostic toP. parviflora var.pentaphylla andP. pumila by PCR amplification of the intron ofnad1 on mtDNA, and examined the spatial-distribution pattern of the mtDNA haplotypes in a hybrid zone betweenP. parviflora var.pentaphylla andP. pumila in the Tanigawa Mountains of Japan. These data, in conjunction with previous information on cpDNA haplotypes and needle morphology, revealed contrastive patterns of introgression of two cytoplasmic genomes. CpDNA introgression has occurred uni-directionally fromP. parviflora var.pentaphylla toP. pumila. Conversely, mtDNA introgression has occurred in the opposite direction, fromP. pumila toP. parviflora var.pentaphylla. Levels of introgression are roughly equivalent for cpDNA and mtDNA. The contrastive spatial distribution pattern of cpDNA and mtDNA haplotypes could be caused by differential movement of seeds and pollen for interspecific genetic exchange.     

Genetic parameters of intra- and inter-specific hybrids of Eucalyptus globulus and E. nitens

Intra-specific hybrids within Eucalyptus nitens and E. globulus were compared directly with inter-specific E. nitens × globulus using common parents. Diameter (age 2, 4, 6, 10 years) and Pilodyn (age 6 years) were used as indirect measures of growth and wood density, respectively. Genetic parameters were estimated for all cross types and traits. A direct comparison of the general combining ability with the general hybridising ability was made. Heterosis was estimated for intra- and inter-specific hybrids. The intra-specific hybrids in both species exhibit intermediate heritabilities and levels of additive genetic variance. The inter-specific F1 E. nitens × globulus exhibited high incidence of abnormalities at young ages and high levels of later age mortality. The mean performance of surviving inter-specific F1 hybrids was generally intermediate for all traits, to varying degrees, between the parental intra-specific crosses, and there is little evidence for significant heterosis. Different provenances of E. globulus may exhibit different responses to hybridisation. In this case, the inter-specific F1 hybrids, using Taranna E. globulus, appear to perform worse on average than those using King Island provenance for growth traits. There is evidence that specific hybrid families are produced that outperform most of the pure species families for one or other of the traits examined; however, there is no reliable quantitative genetic method of predicting which parents should be used.     

The cytotaxonomy and origin ofRanunculus yaegatakensis,an endemic taxon of Yakushima Island

Ranunculus yaegatakensis, a close relative of the widespreadR. silerifolius, is endemic to the alpine region (ca. 1,600 m alt.) of Yakushima Island. This species differs morphologically fromRanunculus silerifolius mainly due to its dwarfism and leaf shape, but has an identical karyotype with one (Karatsu-type) of the four cytotype ofR. silerifolius. Ranunculus yaegatakensis is highly cross-compatible with the Karatsu-type plants ofR. silerifolius. Their F₁ hybrids show regular meiotic behaviors and set seeds successfully. In addition, the Karatsu-type ofRanunculus silerifolius is found in individuals that are collected not only from the lowland of Yakushima Island but from its neighboring islands. It is supposed to be more specialized than other cytotypes. This evidence suggests thatRanunculus yaegatakensis has been derived from the Karatsu-type plants ofR. silerifolius. We suggest thatRanunculus yaegatakensis be reduced to a variety ofR. silerifolius.     

Three species groups in American trilliums as revealed by compatibility with an Asian species

American trilliums are all diploid and are classified into three groups with regard to compatibility withTrillium kamtschaticum, a single diploid Asian species: (1) Compatible pedicellate-flowered species, i.e.T. erectum, T. gleasoni, andT. vaseyi. (2) Incompatible pedicellate-flowered species, i.e.T. grandiflorum. (3) Incompatible sessile-flowered species, i.e.T. decunbens, T. luteum, T. sessile andT. stamineum. HybridsT. kamtschaticum×T. erectum flowered for the first time 9–10 years after sowing F₁ seeds. The F₁ were completely sterile in pollen and in seed-setting.     

Genotype frequency and F ST analysis of polymorphisms in immunoregulatory genes in Chinese and Caucasian populations

Selection and genetic drift can create genetic differences between populations. Cytokines and chemokines play an important role in both hematopoietic development and the inflammatory response. We compared the genotype frequencies of 45 SNPs in 30 cytokine and chemokine genes in two healthy Chinese populations and one Caucasian population. Several SNPs in IL4 had substantial genetic differentiation between the Chinese and Caucasian populations (F _ST ~0.40), and displayed a strikingly different haplotype distribution. To further characterize common genetic variation in worldwide populations at the IL4 locus, we genotyped 9 SNPs at the IL4 gene in the Human Diversity Panel’s (N = 1056) individuals from 52 world geographic regions. We observed low haplotype diversity, yet strikingly different haplotype frequencies between non-African populations, which may indicate different selective pressures on the IL4 gene in different parts of the world. SNPs in CSF2, IL6, IL10, CTLA4, and CX3CR1 showed moderate genetic differentiation between the Chinese and Caucasian populations (0.15 < F _ST < 0.25). These results suggest that there is substantial genetic diversity in immune genes and exploration of SNP associations with immune-related diseases that vary in incidence across these two populations may be warranted.     

Resource utilization of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr

Summary Resource utilization by cutthroat trout (CT) and Dolly Varden charr (DV) was studied 8 years after experimental transfers from sympatry had established reproducing allopatric populations in two nearby fishless lakes. Allopatric DV significantly increased their utilization of shallow-dwelling zoobenthos, and increased their vertical distribution in comparison to that in sympatry. In contrast, allopatric CT showed little change in the proportions of major prey types utilized, and, if anything, restricted their vertical distribution in comparison to that in sympatry. The results can be explained by the hypothesis that the resource use of DV is strongly influenced by interspecific competition from CT, whereas CT largely remains unaffected by this interaction. An alternative hypothesis, that lake differences can explain the differences in resource use between sympatry and allopatry, was evaluated by comparing food resource availability and other biotic and abiotic characteristics of the three study lakes. None of these could account for the shift in resource use by DV between sympatry and allopatry, but lake differences may explain why allopatric CT showed a restricted habitat use in comparison with their sympatric donor stock. The results of this whole-lake transfer experiment are consistent with earlier reported field and laboratory studies, and suggest that the aggressive dominance of CT is the most important mechanism by which DV are displaced from littoral and near-surface habitats in sympathy with CT.     

Predicting the potential of open-pollinating populations for the production of superior F1 hybrids

Summary The distributive properties of a single population or of a population resulting from a cross between two populations are reproduced when inbreds randomly extracted from the population itself or from the two parental populations are randomly paired. Hence, population parameters that are usually obtained during a breeding programme can be used to predict the performance of the F₁ hybrids that can be derived from them at that stage. Multiple allelism, epistasis and deviations from Hardy-Weinberg equilibria should not cause biasis to the predictions. While in theory genotype x environment interaction and linkage disequilibrium may disturb the predictions, in practice they are unlikely to create problems that cannot be accommodated. Genotypic and phenotypic predictions of the proportions of the F₁ hybrid distribution scoring above or below a given standard are made and analysed for three characters, weight of the ears, plant height and height of the ear, in two populations of maize per se and their interpopulational cross. Because no random inbred lines from the experimental populations are presently available we cannot check our predictions. However, genotypic and phenotypic predictions and observations of F₁ hybrids obtained from populations created by computer simulation are provided to illustrate our procedures.J. F. F. de Toledo is a geneticist on leave from Centro National de Pesquisa de Soja-EMBRAPA, Caixa Postal 1061, 86100-Londrina-Pr, BrazilJ. B. de Miranda Filho is Professor of Genetics at Escola Superior de Agriculture Luiz de Queiroz-ESALQ, Caixa Postal 83, 13400-Piracicaba-SP, Brazil     

Confirmation of hybridization among sympatric insular populations of Orchis mascula and O. provincialis

The localized hybridization between Orchis mascula and O. provincialis in Sardinia is investigated. The two parental species are closely related and share the same pollinators but do not hybridize in any other areas of sympatry. Artificial crosses between the two species in areas of sympatry on the continent revealed that, in absence of an ethological isolation, a strong post-pollination barrier exists and preserves species integrity in the main part of their distribution. However, on Sardinia, morphological observations, karyological and molecular analyses of intermediate phenotypes confirmed the occurrence of hybridization between the insular O. mascula ssp. ichnusae and O. provincialis and the bi-directionality of pollen flow. The occurrence of hybrids on the island indicates a failure of otherwise strong post-pollination barriers between O. mascula and O. provincialis.     

Genetic variation in sympatric populations of diploid and polyploid brine shrimp (Artemia parthenogenetica)

We examined genetic variation in sympatric diploid and polyploid brine shrimp Artemia parthenogenetica from each of three populations (China, Italy and Spain). Italian and Spanish tetraploids are closely related (I=0.964). Diploids and tetraploids within each of the two European populations are also closely related (mean I=0.905). Most alleles found in diploids also exist in sympatric polyploids. In contrast, the asexual Artemia (2N, 4N and 5N) in our study share few alleles with their close sexual relative, A. tunisiana (mean I=0.002). These results, as well as the work of other authors, strongly suggest that at least the tetraploid Artemia in our study have an autopolyploid origin.Clonal diversity of polyploid Artemia can be very high at least in some population. Both diploids and polyploids had low clonal diversities in the populations dominated by polyploids and high clonal diversities in the population dominated by diploids.The most common genotypes of sympatric diploid and polyploid Artemia frequently differed. Some alleles occurred only in diploids, while others were restricted to polyploids. These results suggest that polyploidy in Artemia has led to genetic divergence from diploid progenitors, and that ploidy-level variation must also be considered in developing an understanding of spatial and temporal allozyme polymorphism in asexual populations.     

Contrasting Levels of Variation in Neutral and Quantitative Genetic Loci on Island Populations of Moor Frogs (<Emphasis Type="Italic">Rana arvalis</Emphasis>)

Reduced levels of genetic variability and a prominent differentiation in both neutral marker genes and phenotypic traits are typical for many island populations as compared to their mainland conspecifics. However, whether genetic diversity in neutral marker genes reflects genetic variability in quantitative traits, and thus, their evolutionary potential, remains typically unclear. Moreover, the phenotypic differentiation on islands could be attributable to phenotypic plasticity, selection or drift; something which seldom has been tested. Using eight polymorphic microsatellite loci and quantitative genetic breeding experiments we conducted a detailed comparison on genetic variability and differentiation between Nordic islands (viz. Gotland, Öland and Læsø) and neighbouring mainland populations of moor frogs (Rana arvalis). As expected, the neutral variation was generally lower in island than in mainland populations. But as opposed to this, higher levels of additive genetic variation (V _A) in body size and tibia length were found on the island of Gotland as compared to the mainland population. When comparing the differentiation seen in neutral marker genes (F _ST) with the differentiation in genes coding quantitative traits (Q _ST) two different evolutionary scenarios were found: while selection might explain a smaller size of moor frogs on Gotland, the differentiation seen in tibia length could be explained by genetic drift. These results highlight the limited utility of microsatellite loci alone in inferring the causes behind an observed phenotypic differentiation, or in predicting the amount of genetic variation in ecologically important quantitative traits.     

7种秋海棠叶片斑纹结构及遗传特性分析

以7种(品种)秋海棠为材料,观察叶片斑区和非斑区组织结构、测定叶绿素含量及叶绿素荧光参数F_v/F_m值,分析叶片斑纹的形成原因及银点秋海棠点状斑的遗传特性。结果显示：(1)银点秋海棠、铺地秋海棠、假厚叶秋海棠、‘皮卡’和‘非洲丛林’叶片斑区的上表皮细胞与栅栏组织细胞间存在空隙,非斑区则没有空隙,彩纹秋海棠和‘虎斑’的斑区与非斑区上表皮细胞和栅栏组织细胞间均紧密相连。(2)7种(品种)秋海棠叶片斑区和非斑区都具有完整的叶绿体超微结构,类囊体膜丰富,基质和基粒片层清晰;银点秋海棠、假厚叶秋海棠、‘皮卡’和‘非洲丛林’斑区的叶绿素a、b及总叶绿素含量均低于非斑区,而铺地秋海棠斑区和非斑区差别不大;除假厚叶秋海棠的斑区叶绿素荧光参数F_v/F_m值小于非斑区外,其余6种秋海棠均为斑区高于非斑区。(3)银点秋海棠与无斑种类杂交,杂交后代叶片有斑和无斑的植株约为1∶1,而其自交后代中有斑和无斑的植株比例近3∶1。研究发现,银点秋海棠、铺地秋海棠、假厚叶秋海棠、‘皮卡’和‘非洲丛林’的叶斑属于空隙结构型,彩纹秋海棠和‘虎斑’叶斑属于色素型。银点秋海棠点状叶斑与无斑是1对可遗传的相对性状,白色点状斑为显性性状。     

Low levels of quantitative and molecular genetic differentiation among natural populations of Medicago ciliaris Kroch. (Fabaceae) of different Tunisian eco-geographical origin

In this paper, we analyze the genetic variability in four Tunisian natural populations of Medicago ciliaris using 19 quantitative traits and six polymorphic microsatellite loci. We investigated the amplification transferability of 30 microsatellites developed in the model legume M. truncatula to M. ciliaris. Results revealed that about 56.66% of analyzed markers are valuable genetic markers for M. ciliaris. The most genetic diversity at quantitative traits and microsatellite loci was found to occur within populations (>80%). Low differentiations among populations at quantitative traits Q _ST  = 0.146 and molecular markers F _ST  = 0.18 were found. The majority of measured traits exhibited no significant difference in the level of Q _ST and F _ST . Furthermore, significant correlations established between these traits and eco-geographical factors suggested that natural selection should be invoked to explain the level of phenotypic divergence among populations rather than drift. There was no significant correlation between population differentiation at quantitative traits and molecular markers. Significant spatial genetic structure consistent with models of isolation by distance was detected within all studied populations. The site-of-origin environmental factors explain about 9.07% of total phenotypic genetic variation among populations. The eco-geographical factors that influence more the variation of measured traits among populations are the soil texture and altitude. Nevertheless, there were no consistent pattern of associations between gene diversity (He) and environmental factors.     

同域分布垂穗披碱草和达乌力披碱草遗传多样性和遗传结构分析

披碱草属(Elymus L.)是禾本科(Poaceae)小麦族(Triticeae)中的一个多年生属,该属在青藏高原地区有广泛分布,多数物种是草原和草甸的组成成分,许多种类为品质优良的牧草.垂穗披碱草(E.nutans)和达乌力披碱草(E.dahuricus)同为禾本科小麦族披碱草属异源六倍体物种,染色体组组成皆为St...     

Genetic and clonal diversity in Korean populations ofVitex rotundifolia (Verbenaceae)

Vitex rotundifolia L.f. is a woody perennial and has sexual and asexual modes of reproduction. Allozyme study was conducted on 550 plants in 13 Korean populations. The levels of genetic variability and divergence within and among populations, respectively, are considerably lower and higher than the mean values for woody plants with similar life history tralts. Mean percentage of polymorphic loci (P _P), mean number of alleles per locus (A _P), and mean genetic diversity (He _P) within populations ofV. rotundifolia were: 16.7%, 1.21, and 0.047. On average, about 79% of the total variation inV. rotundifolia was common to all populations (meanG _ST=0.208). In addition, significant differences in allele frequencies among populations were found in all polymorphic loci examined (P<0.001). On the other hand, levels of genotypic diversity within and among populations were moderate. About 44% (18/41) of multilocus genotypes were “local genotypes” (genotypes occurring in only one population), whereas only one “widespread genotype” (genotypes occurring in more than 75% of the populations) were detected. The mean number of multilocus genotypes per population (G) and mean genotypic diversity index (D _G) were 8.4 and 0.74, respectively. Most common multilocus genotypes found in populations were homozygous for five polymorphic loci. The abundance of ramets of these genets is responsible for the low levels of expected heterozygosity within populations. The results indicate that clonal reproduction may act as an enhancer of genetic drift by reducing effective size of local populations ofV. rotundifolia.     

Genetic structure of chukar partridge ( Alectoris chukar) populations in the Longdong Loess Plateau, China

This study used polymerase chain reaction (PCR) and dideoxy direct sequencing methods to analyze the genetic structure of the chukar partridge (Alectoris chukar) in the Longdong Loess Plateau, northwestern China. A total of 491 nucleotides of mitochondrial DNA from the control region gene were sequenced for 78 chukar partridges from eight different populations. The 24 variable positions defined 25 haplotypes. The high gene flow (Nm=3.75) implied little genetic differentiation between the eight populations. All the populations shared the haplotype C_1, which suggested that they all came from a common ancestor. The 25 haplotypes were spread through the populations, but could be clustered into two groups. The haplotype similar index between the two groups was only 0.15, with a genetic distance of 0.43%. The genetic variation was significantly different between the two groups, which had been isolated for all of recorded history. The genetic structure of chukar partridge populations in the Plateau appears to be the result of the synergistic effect of a glacier, along with debris flow and human activities since the middle of the Pleistocene.Communicated by F. Bairlein     

Genetic variation in two sympatric European populations of Bosmina spp. (Cladocera) tested with RAPD markers

We used RAPDs (Random Amplified Polymorphic DNA) to test genetic divergence between two populations of Bosmina spp. in Lake Östersjön, Sweden. Previous taxonomic studies on European species within the genus Bosmina have been based on morphological characters alone. RAPD markers distinguished the two populations and supported the specific status of B. coregoni and B. longispina based on morphological characters. Furthermore, juveniles with a long antennule and a mucro were classified as B. coregoni. RAPDs also revealed genetic differences among the tested individuals, suggesting several clones within each species.     

Genetic differentiation between two varieties of Oreocharis benthamii (Gesneriaceae) in sympatric and allopatric regions

The pattern of genetic differentiation between diverging species receives much attention as one of the key observable features of speciation. It has often been suggested that introgression between closely related species occurs commonly where their distributions overlap, leading to their becoming more morphologically and genetically similar, but there are a few opposite results. However, most of these studies have been carried out with animals and separate species; few have looked at intraspecific cases, especially in plants. Here, we conduct a comparative study on patterns of genetic differentiation among populations of two varieties of Oreocharis benthamii in allopatry and sympatry based on ISSR data for 754 individuals from 26 populations, in order to understand the processes leading to speciation. Contrary to expectations, the facultative xenogamy (mixed mating) species O. benthamii has a relatively low genetic diversity within populations (H = 0.1014, I = 0.1528) and high genetic differentiation among populations (G_ST = 0.5867, Ф_ST = 0.659), as is typically found for selfing species. Genetic variance between the two varieties in sympatric populations (44%, Ф_ST = 0.444) is significantly more than that in allopatric populations (14%, Ф_ST = 0.138). Consistent with the taxonomical delimitation of the two varieties, all sampled individuals of O. benthamii clustered into two genetic groups. Moreover, the genetic structures of populations of both varieties are correlated with their different geographical origins. Our studies show that significant divergence between sympatric populations of the two varieties could be attributed primarily to reinforcement by genetic divergent selection in sympatry where secondary contact had occurred. The major proportion of the genetic variation in outcrossing and mixed mating plants may exist among populations when the populations are distributed in fragmented habitats, due to the paucity of suitable habitat combined with inefficient seed dispersal mechanism and limited pollinator foraging area that may limit the gene flow.     

Genetic variability in British populations ofPotamogeton coloratus (Potamogetonaceae)

The partitioning of genetic variability within and between twelve British populations of the anemophilous aquaticPotamogeton coloratus Hornem. was investigated by isozyme analysis. Low levels of variability as measured by P, A and H were found. Calculation of Wright's F statistics revealed a high mean value of the overall inbreeding coefficient, (F_IT = 0.939), which was attributed both to high levels of genetic subdivision among populations (mean F_ST = 0.702) and to a high frequency of inbreeding or clonal growth within them (mean F_IS = 0.796). Only two populations are polymorphic; both inhabit sites with a long post-glacial history as wetlands. Populations of recent origin, as well as some of older vintage, contain only a single multi-locus isozyme genotype, homozygous at all loci except for IDH. A genetic bottleneck following the Devensian glaciation is discussed as a possible cause of the pattern of variation. Evidence for a duplicated IDH locus is presented.