辣椒种间杂种的表型鉴定及SRAP分析

运用有性杂交方法,以微辣一年生辣椒自交系B9431为母本(P1)、强辣野生灌木辣椒H108为父本(P2)进行种间杂交,获得了其种间杂种.对种间杂种F125个表型性状进行了观察比较,以期从形态学及分子生物学方面验证种间杂种的真实性.结果表明,F1兼具双亲的形态特征,大多数表型性状介于P1与P2之间.SRAP分析显示,F1与P1、P2共有带550条,占总位点数的68.4%,与P1或P2共有带159条,占19.8%;F1与P1遗传相似系数为0.856,与P2的遗传相似系数为0.786,表明杂种在DNA水平上更趋向于母本.     

Genetic assessment of the effects of self-fertilization in a Lilium L. hybrids using molecular cytogenetic methods (FISH and ISSR)

Self-fertilization (also termed selfing) is a mode of reproduction that occurs in hermaphrodites and has evolved several times in various plant and animal species. A transition from outbreeding to selfing in hermaphroditic flowers is typically associated with changes in flower morphology and functionality. This study aimed to identify genetic effects of selfing in the F2 progeny of F1 hybrid developed by crossing Lilium lancifolium with the Asiatic Lilium hybrid ‘Dreamland.’ Fluorescence in situ hybridization (FISH) and inter-simple sequence repeats (ISSR) techniques were used to detect genetic variations in plants produced by selfing. The FISH results showed that F1 hybrid were similar to the female parent (L. lancifolium) regarding the 45S loci, but F2 individuals showed variation in the number and location of the respective loci. In F2 progeny, F2-2, F2-3, F2-4, F2-5, and F2-8 hybrids expressed two strong and one weak 5S signal on chromosome 3, whereas F2-7 and F2-9 individuals expressed one strong and two weak signals. Only two strong 5S signals were detected in an F2-1 plant. The ISSR results showed a maximum similarity value of 0.6269 between the female parent and the F2-2 hybrid. Regarding similarity to the male parent, a maximum value of 0.6119 was found in the F2-1 and F2-2 hybrids. The highest genetic distance from L. lancifolium and the Asiatic Lilium hybrid ‘Dreamland’ was observed in the F2-4 progeny (0.6352 and 0.7547, respectively). Phylogenetic relationships showed that the F2 progeny were closer to the male parent than to the female parent. Self-fertilization showed effects on variation among the F2 progeny, and effects on the genome were confirmed using FISH and ISSR analyses.     

Unusual patterns of hybridization involving a narrow endemic Rhododendron species (Ericaceae) in Yunnan, China

? Premise of the study: One potential threat to rare species is genetic swamping caused by hybridization, but few studies have quantified this threat. Rhododendron cyanocarpum is a narrow endemic species that occurs sympatrically with potentially interfertile congeners throughout its range within Yunnan, China. We searched the entire distribution of R. cyanocarpum for hybrids and examined the patterns of hybridization to assess potential threat from hybridization. ? Methods: In a comprehensive field survey, we detected only one instance of hybridization involving R. cyanocarpum, with R. delavayi, at Huadianba near Dali. Material of both species and putative hybrids was examined using morphology, chloroplast DNA, nuclear ribosomal DNA, and Bayesian analysis of AFLP profiles. ? Key results: Of 10 putative hybrids, two were F(1)(')s and at least seven were F(2)(')s. Four backcrosses to R. delavayi were detected among material with R. delavayi-like morphology within the hybrid zone. Backcrosses to R. cyanocarpum were not detected. Therefore F(2)(')s outnumbered all other classes within the hybrid zone, a situation not previously confirmed for plants and extremely rare generally. Hybridization was asymmetrical, with R. delavayi as the maternal parent in all but one of the hybrids detected. ? Conclusions: Although natural hybridization is common in Rhododendron, it is rare in R. cyanocarpum and is apparently not accompanied by backcrossing toward R. cyanocarpum. Hence, there is no immediate risk of genetic swamping, unless habitat disturbance increases and changes the patterns of hybridization. Our study is the first to report a plant hybrid zone dominated by F(2) hybrids. This pattern might contribute to species barrier maintenance.     

A mating system conundrum: hybridization in Apocynum (Apocynaceae)

Based upon an intermediate morphology, Apocynum x-floribundum Greene has long been considered a hybrid involving A. androsaemifolium and A. cannabinum. The floral morphology in this genus, however, appears to prohibit both import and export of pollen, and observations of numerous insect visitors reveal that pollen is not routinely carried from flower to flower. Furthermore, reproductive success as measured by fruit set is very low in most populations. Hybridization was thus called into question, with allozyme evidence used to test the hypothesis of a hybrid origin for A. x-floribundum. Six diagnostic loci, as well as two loci exhibiting highly disparate allele frequencies, were resolved for each parent. All examined populations of A. x-floribundum were heterozygous at these loci, thus supporting the hypothesis of hybridization. Evidence from additional loci indicated that all populations tend to be strongly clonal. Observed heterozygosity was very low in the parental species, suggesting a history of inbreeding or a severe bottleneck. There was no support for earlier assumptions that some intermediates are derived from backcrosses or "secondary hybrids." Statistical analyses of plant height, leaf shape, petal length, sepal length, follicle length, seed length, and seed number per follicle supported these conclusions. The persistence and vegetative spread of hybrid clones may contribute to the illusion that hybridization is common.     

Patterns of introgression across an expanding hybrid zone: analysing historical patterns of gene flow using nonequilibrium approaches

Previous studies suggest that the hybrid zone between two taxa in the Piriqueta caroliniana complex in central Florida (south-eastern North America) has recently expanded with hybrids replacing parental genotypes across a broad region of the Florida peninsula. Here I use patterns of genetic disequilibria and levels of differentiation among populations to infer historical patterns of introgression across this broad hybrid zone. There were strong positive associations among taxon-specific alleles at the southern extent of hybridization, but disequilibria values were close to zero across the central and northern portions of the hybrid zone. Levels of among-population differentiation in the central portion of the hybrid zone were relatively low, and increased towards the northern extent of hybridization. The high levels of disequilibria are coincident with the sharp clines at the southern end of the hybrid zone, suggesting that there is a tension zone in this region that is maintained by selection against hybrids and dispersal from parental regions. The levels of disequilibria within populations and patterns of differentiation among populations are consistent with historical introgression and northward expansion of this hybrid zone, which may have slowed or ceased in recent generations.     

Window of opportunity: an episode of recruitment in a Banksia hybrid zone demonstrates continuing hybridization and phenotypic plasticity

Background and Aims

In perennial plants (especially post-fire resprouters), extant populations may reflect recruitment events in the distant past. This is true of hybrid zones formed by two Banksia species of swamps and woodlands in south-eastern Australia, Banksia robur and B. oblongifolia. Both resprout after fire but recruitment is dependent on periodic fires. Although plants of intermediate morphology have also been identified as hybrids using allozyme markers, the extent of ongoing hybridization is unknown. This study investigates whether both microsatellite markers and morphological measurements can be used to distinguish between the two species and their hybrids. A recent recruitment event and microsatellite markers allow the frequency of ongoing hybridization to be estimated, and also the effects of environmental variation on the morphology of plants and seedlings to be tested.

Methods

Variation at seven microsatellite loci was scored and seven leaf characteristics within putatively pure stands and mixed stands of both species were measured, revealing that the two species were genetically and morphologically distinct and that mixed stands also contained genetically and sometimes morphologically distinct hybrids. An opportunity created by wildfires was used to analyse the genetics and morphometrics of adults and seedlings from two hybrid zones.

Key Results

Approximately 9 % of adults and 21 % of seedlings were identified as genetic hybrids in both hybrid zones. Within these sites, the genotype of mature plants correlated well with morphology, except for some hybrid plants that had parental morphology. However, seedling morphology was highly variable and insufficient to describe the composition of the hybrid zone in this cohort. Greater phenotypic plasticity was evident among seedlings growing within the hybrid zones than seedlings growing in pots.

Conclusions

The hybrid zones are complex and the range of genotypes detected in seedlings reveals both continuing hybridization and introgression.     

Proteomic analyses of the Xiphophorus Gordon-Kosswig melanoma model

Interspecies hybridization between the platyfish X. maculatus Jp 163 A, and the swordtail X. helleri (Sarabia), generates F(1) hybrids with pronounced melanin pigmentation. Backcrossing of F(1) hybrids with the X. helleri parent results in 25% of progeny that will spontaneously develop melanoma. We have applied proteomic methods to this Gordon-Kosswig (G-K) melanoma model to identify candidate proteins that exhibit modulated expression in fin tissue due to interspecies hybridization and progression of hybrid tissues to spontaneous melanoma. Difference Gel Electrophoresis (DIGE) was used to minimize the variability commonly observed in quantitative analyses of comparative protein samples. Following identification of up- or down-regulated protein expression by DIGE, candidate protein spots were identified by mass spectrometric sequencing. Several protein expression differences displayed in interspecies hybrids were identified and compared to distinct differences that occur upon backcrossing and progression to melanoma. These studies are important for the identification of distinct biochemical pathways involved in the variety of Xiphophorus interspecies hybrid tumor models.     

Genotype-by-environment interaction and the fitness of plant hybrids in the wild

Natural hybrid zones between related species illustrate processes that contribute to genetic differentiation and species formation. A common viewpoint is that hybrids are essentially unfit, but they exist in a stable tension zone where selection against them is balanced by gene flow between the parent species. An alternative idea is that selection depends on the environment, for example, by favoring opposite traits in the two parental habitats or favoring hybrids within a bounded region. To determine whether selection of hybrids is environment dependent, we crossed plants of naturally hybridizing Ipomopsis aggregata and I. tenuituba in the Colorado Rocky Mountains and reciprocally planted the seed offspring into a suite of natural environments across the hybrid zone. All types of crosses produced similar numbers and weights of seeds. However, survival of the offspring after 5 years differed markedly among cross types. On average, the F1 hybrids had survival and growth rates as high as the average for their parents. But hybrid survival depended strongly on the direction of a cross, that is, on which species served as the maternal parent. This fitness difference between reciprocal hybrids appeared only in the parental environments, suggesting cytonuclear gene interactions that are environment specific. These results indicate that complex genotype-by-environment interactions can contribute to the evolutionary outcome of hybridization.     

Morphological, molecular and cytological analyses of Carica papaya×C. cauliflora interspecific hybrids

 Morphological, molecular and cytological analyses were performed to assess the hybridity of 120 putative interspecific hybrids of Carica papaya L.×C. cauliflora Jacq. In the putative interspecific hybrids the number of main leaf veins was intermediate between the two parents while the hermaphrodite flower sex form and the low vigour were distinctive features of these hybrids. Petiole length, stem diameter, leaf length, leaf width and flower colour were similar to C. papaya, whereas leaf shape, type, serration, venation, petiole hairiness and flower shape were similar to C. cauliflora. Markers generated by the polymerase chain reaction using 72 10-mer primers (random amplified polymorphic DNA) revealed a high level of polymorphism (64%) between C. papaya and C. cauliflora. Seventeen of these primers yielded reliable and easily scorable polymorphic banding patterns that were further screened to reveal hybrids. A range of 1–5 RAPD primers consistently confirmed that all 120 plants were genetic hybrids, with all of them containing at least one band from the male parent. Cytological analysis revealed that 7–48% of the cells in many of the interspecific hybrids were aneuploid suggesting that chromosome elimination was occurring. The frequency of aneuploid cells was negatively associated (r=0.88) with the number of bands from the male parent integrated into the hybrid. Pollen fertility of the hybrids was from 0.5 to 14.0% while C. papaya and C. cauliflora had 88.0–99.0% and 90.0–97.0% fertile pollen, respectively. Received: 28 February 1996 / Accepted: 27 September 1996     

Evolution of a hybrid zone of two willow species (Salix L.) in the European Alps analyzed by RAD-seq and morphometrics

Natural hybridization of plants can result in many outcomes with several evolutionary consequences, such as hybrid speciation and introgression. Natural hybrid zones can arise in mountain systems as a result of fluctuating climate during the exchange of glacial and interglacial periods, where species retract and expand their territories, resulting in secondary contacts. Willows are a large genus of woody plants with an immense capability of interspecific crossing. In this study, the sympatric area of two diploid sister species, S. foetida and S. waldsteiniana in the eastern European Alps, was investigated to study the genomic structure of populations within and outside their contact zone and to analyze congruence of morphological phenotypes with genetic data. Eleven populations of the two species were sampled across the Alps and examined using phylogenetic network and population genetic structure analyses of RAD Seq data and morphometric analyses of leaves. The results showed that a homoploid hybrid zone between the two species was established within their sympatric area. Patterns of genetic admixture in homoploid hybrids indicated introgression with asymmetric backcrossing to not only one of the parental species but also one hybrid population forming a separate lineage. The lack of F1 hybrids indicated a long-term persistence of the hybrid populations. Insignificant isolation by distance suggests that gene flow can act over large geographical scales. Morphometric characteristics of hybrids supported the molecular data and clearly separated populations of the parental species, but showed intermediacy in the hybrid zone populations with a bias toward S. waldsteiniana. The homoploid hybrid zone might have been established via secondary contact hybridization, and its establishment was fostered by the low genetic divergence of parental species and a lack of strong intrinsic crossing barriers. Incomplete ecological separation and the ability of long-distance dispersal of willows could have contributed to the spatial expansion of the hybrid zone.     

芥菜型油菜和白菜型油菜种间杂种遗传分析

种间杂交是一种拓宽栽培作物遗传基础和转移优良性状的重要手段,已经广泛地用于作物品质的改良。本研究通过芥菜型油菜（Brassica juncea L.）和白菜型油菜（Brassica rapa L.）种间杂交,将芥菜型油菜的有利性状转移到白菜型油菜中,创造新型白菜型油菜,以改良白菜型油菜的农艺性状、提高抗逆性和拓宽其遗传基础。研究结果表明：以芥菜型油菜作母本、白菜型油菜作父本的杂交组合较易获得杂交种子,杂种F1植株营养生长具有较明显的杂种优势,但花粉完全不育;以白菜型油菜回交获得的BC1植株间表型差异明显,平均花粉可染率为34.8%,介于 0~84%之间,群体自交不亲和;BC1F1和BC2群体变异广泛,出现自交亲和植株和黄籽植株,平均花粉可染率分别为79.7%和79.1%。     

AN EMPIRICAL TEST OF PREDICTIONS OF TWO COMPETING MODELS FOR THE MAINTENANCE AND FATE OF HYBRID ZONES: BOTH MODELS ARE SUPPORTED IN A HARD-CLAM HYBRID ZONE

Two models developed to discern the mode of selection in hybrid zones differ in some predictions. The tension-zone model predicts that selection acts against hybrids and independently of the environment (endogenous selection) and that selection is invariant throughout the hybrid zone. The ecological selection-gradient, or ecotone, model maintains that fitness of different genotypes varies in response to environmental variation (exogenous selection) and thus, that in a region of the zone, fitness of hybrids is at least equal to that of the parental species. Therefore, to assess the predominant mode of selection operating in a hybrid zone, it is fundamental to evaluate whether selection is acting specifically against hybrid individuals, that is, whether hybridity alone is the basis for deficiencies of hybrids, and to evaluate whether the relative fitness of hybrids versus that of pure species varies across the zone. In a hardclam (genus Mercenaria) hybrid zone located in a polyhaline lagoon in east-central Florida, we used age-specific and location-specific analyses to determine that a hybrid deficit occurrs, that the deficit seems to be due to selection against hybrids, and that selection varies across the zone. Various measures of deviation from Hardy-Weinberg equilibrium, linkage disequilibrium analyses, and shifts in allele frequencies at semidiagnostic loci support the idea that selection is strongest in the northern region of the lagoon, the zone of sympatry and hybridization. Southward, into the range of M. mercenaria (the numerically predominant species), the percentage of hybrids remains relatively high and selection against hybrids decreases. For some genetic linkage groups, selection for M. mercenaria alleles seems to be occurring, but selection seems to be acting principally against alleles characteristic of M. mercenaria and, to a lesser degree, for alleles characteristic of M. campechiensis (the rarer species). These findings and others from previous analyses we have done on this hybrid zone demonstrate that selection in the zone is complex, and that characteristics of both the tension-zone and ecotone models are present. Supporting the tension-zone model, selection against hybrids per se clearly occurs, but specific genotypes seem to be at a selective disadvantage, whereas others have a selective advantage, and selection operates differentially on the two parental species within the zone. Supporting the ecotone model, the strength of overall selection varies throughout the zone, and environmentally mediated selection in which each species and hybrids have an advantage in specific habitats occurs, but some selection against hybrids is invariant throughout the zone. Thus, the structure and genetic architecture of this hybrid zone appear to be products of a complicated interaction between both types of selective forces cited in the two competing models.     

百合‘Siberia’בManissa’种间杂交后代的染色体核型分析

以东方百合杂种系(Oriental hybrids group)品种‘Siberia’为母本,OT杂种系(interspecific hybrids betweenOriental and Longiflorum/OT group)品种‘Manissa’为父本杂交获得种间杂交F1代,对亲本及F1代株系的染色体数目和形态特征进行了分析。结果显示,母本东方百合‘Siberia’为二倍体即24条染色体,而父本‘Manissa’是高度杂合后代,为三倍体即36条染色体。杂交F1代的8个株系中有6个株系为二倍体即24条染色体,有2个株系为非整倍体,染色体条数分别为25和26条。母本‘Siberia’的核型为4m(1SAT)+10st(1SAT)+10t,父本‘Manis-sa’的核型为3m+18st(1SAT)+15t(1SAT),均属3B型。杂种F1代核型出现了多种类型,其中株系a、b、h为3B型,株系c、d、e、f为3A型,株系g为4B型。与亲本染色体形态相比,F1代株系出现了随体及端部着丝点染色体较多等染色体形态结构特征,而亲本没有这些特征。从染色体的形态、随体来看,子代为真杂种,在遗传上均偏向于母本。     

Chloroplast DNA variation and hybridization between invasive populations of Japanese knotweed and giant knotweed (Fallopia, Polygonaceae)

Chloroplast inheritance and the direction of hybridization have been investigated in some invasive weeds from the genus Fallopia. PCR RFLP analysis of the tmK intron has been used to identify markers that distinguish between the chloroplast genomes of British samples of F. japonica var. japonica, F. japonica var. compacta and F. sachalinensis. Maternal inheritance of chloroplast DNA has been observed in controlled crosses and in hybrid seed from known maternal parents. PCR RFLP analysis of wild hybrids between F. japonica var. japonica and either F. japonica var. compacta or F. sachalinensis indicates that F. japonica var. japonica is the maternal parent of all of its hybrids, consistent with the apparent male-sterility of this taxon in Britain. Hybrids between F. japonica var. compacta and F. sachalinensis show the chloroplast haplotype of one or other of the parents, consistent with bi-directional hybridization.     

Variation in morphological traits in a recent hybrid zone between closely related Quercus liaotungensis and Q. mongolica (Fagaceae)

Aims Hybridization usually leads to gene introgression between related species in hybrid zones, associated with complex patterns of morphological variation. Nevertheless, previous studies have tended to ignore the effects of geographic variation in hybridization rates on species taxonomy. This study aims to investigate the variation of morphological traits between two sympatric and taxonomically confused oak species, Quercus liaotungensis and Q. mongolica, and reveal the effects of hybridization rates on morphological traits and the taxonomic boundary.Methods We used seven microsatellite loci to evaluate species status and measured 15 morphological traits in 26 trees in the recent hybrid zone between Q. liaotungensis and Q. mongolica, and we characterized the differences between the two oak species and their hybrids for the investigated traits.Important findings Molecular analyses indicated that 74% of 78 sampled maternal trees were hybrids between Q. liaotungensis and Q. mongolica although the observed morphological variation suggested that they had remained distinct species. Across all of the differentiated leaf and reproductive traits, the hybrids expressed patterns similar to Q. liaotungensis, which may suggest dominant expression of parental characters. These results are consistent with our expectation that hybrids will be difficult to distinguish from parental species in a recent hybrid zone.     

Hybrid bridges to gene flow: a case study in milkweeds (Asclepias)

Natural hybridization occurs throughout areas of sympatry for the North American milkweeds Asclepias exaltata and A. syriaca (Asclepiadaceae), even though the formation of F1 hybrid seed is a rare event. For introgressive hybridization to proceed, F1 and advanced hybrids must be released from reproductive barriers and successfully mate with one or both parental species. I investigated the mating system of natural hybrids between A. exaltata and A. syriaca in three populations in Shenandoah National Park, Virginia. Allozyme data and a maximum-likelihood procedure were used to estimate the frequency of six genotypic classes (parentals, F1, F2, and backcrosses) of the hybridizing populations, the pollinia received by hybrid plants, and the paternal parents of seeds produced by hybrids. F1 hybrids, backcross A. syriaca, and parental A. syriaca individuals were common in three hybrid populations. Even though self-pollinations and interhybrid pollinations were common, F2 seed production and the occurrence of F2 individuals were rare in hybrid populations. Hybrid plants received more pollen from A. syriaca than A. exaltata, which resulted in the production of more backcross-A. syriaca seed than backcross-A. exaltata seed. Asclepias exaltata was rare in the hybrid populations, but A. exaltata pollinia were received by hybrids and this species sired between 15% and 36% of the seeds produced on hybrids. The potential for introgression with A. exaltata populations is lower because this species is unsuccessful as the maternal parent in interspecific and backcross hand-pollinations. The asymetry of hybridization with A. syriaca as the maternal parent is further supported by the incorporation of maternally inherited chloroplast DNA markers in hybrids. Hybrid milkweeds frequently backcross with both parental species and may be released from the reproductive barriers that limit the formation of F1 hybrids in natural populations. The direction of interspecific gene flow and introgression in milkweeds is influenced by the reproductive biology of hybrids, the constituency of the surrounding population, and failure of some crosses to produce seeds. Finally, introgressive hybridization remains an important evolutionary force even when the initial formation of F1 hybrids in natural populations is rare.     

Population Genetics of a Translocated Population of Mottled Ducks and Allies

Translocating species is an important management tool to establish or expand the range of species. Success of translocations requires an understanding of potential consequences, including whether a sufficient number of individuals were used to minimize founder effects and if interspecific hybridization poses a threat. We provide an updated and comprehensive genetic assessment of a 1970s–1980s translocation and now established mottled duck (Anas fulvigula) population in South Carolina, USA. In addition to examining the population genetics of these mottled ducks, we simulated expected genetic assignments for generational hybrids (F1–F10), permitting formal purity assignment across samples to identify true hybrids and establish hybridization rates. In addition to wild mallards (A. platyrhynchos), we tested for presence of hybrids with migrant American black ducks (A. rubripes) and released domestic game-farm mallards (A. p. domesticus). We used wild reference populations of North American mallard-like ducks and sampled game-farm mallards from 2 sites in South Carolina that could potentially interbreed with mottled ducks. Despite 2 different subspecies of mottled duck (Florida [A. f. fulvigula] and the Western Gulf Coast [A. f. maculatlus]) used in original translocations, we determined the gene pool of the Western Gulf Coast mottled duck was overwhelmingly represented in South Carolina's current population. We found no evidence of founder effects or inbreeding and concluded the original translocation of 1,285 mottled ducks was sufficient to maintain current genetic diversity. We identified 7 hybrids, including an F1 and 3 late-staged (i.e., F2–F3 backcrosses) mottled duck × black duck hybrids, 1 F2-mottled duck backcrossed with a wild mallard, and 2 F3-mottled ducks introgressed with game-farm mallard. We estimated a 15% hybridization rate in our mottled duck dataset; however, the general lack of F1 and intermediate hybrids were inconsistent with scenarios of high hybridization rates or presence of a hybrid swarm. Instead, our results suggested a scenario of infrequent interspecific hybridization between South Carolina's mottled ducks and congeners. We concluded that South Carolina's mottled duck population is sufficiently large now to absorb current hybridization rates because 85% of sampled mottled ducks were pure. These results demonstrate the importance in managing and maintaining large parental populations to counter hybridization. As such, future population management of mottled ducks in South Carolina will benefit from increased geographical and continued sampling to monitor hybridization rates with closely related congeners. We also suggest that any future translocations of mottled ducks to coastal South Carolina should originate from the Western Gulf Coast. © 2021 The Wildlife Society.     

Morphological variation among Betula nana (diploid), B. pubescens (tetraploid) and their triploid hybrids in Iceland

BACKGROUND AND AIMS: Introgressive hybridization between two co-existing Betula species in Iceland, diploid dwarf birch B. nana and tetraploid downy birch B. pubescens, has been well documented. The two species are highly variable morphologically, making taxonomic delineation difficult despite stable ploidy levels. Here an analysis is made of morphological variation within each ploidy group with an aim to establishing a reliable means to distinguish the species. METHODS: Plant materials were collected from 14 woodlands in Iceland. The plants were identified based on 2n chromosome numbers. Morphological variation in species-specific characters within each ploidy group was analysed qualitatively and quantitatively. The morphological index was based on eight discrete characters, whereas the multivariate analysis was based on nine leaf variables. KEY RESULTS: Of the 461 plants examined, 9.5 % were found to be triploid hybrids. The three ploidy groups were morphologically distinguishable but their variation overlapped. The diploid, triploid and tetraploid groups had average scores of 1.3, 4.1 and 8.3, respectively, in the morphology index scale from 0 (B. nana) to 13 (B. pubescens). A linear discriminant analysis also revealed significant separation among the three ploidy groups and the model assigned 96 % and 97 % of the B. nana and B. pubescens individuals correctly. The triploid hybrids were difficult to predict since only half of them could be assigned correctly. Leaf length was the most useful variable identifying triploid hybrids. Geographical patterns within the ploidy groups could partly be explained by differences in mean July temperature. CONCLUSIONS: Hybridization between B. nana and B. pubescens is widespread in Iceland. The species can be distinguished from each other morphologically, and from the triploid hybrids. The overlapping morphological variation indicates bidirectional introgression between the two species via triploid hybrids. Iceland could be considered a birch hybrid zone, harbouring genetic variation which may be advantageous in subarctic regions.     

Unilateral compatibility and genotypic difference in crossability in interspecific hybridization between Dianthus caryophyllus L. and Dianthus japonicus Thunb

Reciprocal interspecific crosses were carried out between six lines of Dianthus caryophyllus L. and one line of Dianthus japonicus Thunb. Although no seed was set when D. japonicus was used as the seed parent, six seedlings were successfully obtained from 2,380 immature ovules by applying the embryo-rescue technique. However, they showed seed parent-like morphology and no evidence for the hybridity by flow cytometry and RAPD analyses. When six lines of D. caryophyllus were used as seed parents, a total of 192 seedlings were successfully obtained without using the embryo-rescue technique. Among these seedlings, 12 out of 25 progenies obtained from the carnation line '98sp1651' were confirmed to be the hybrids. The remaining 13 progenies of this line, and the total 167 progenies obtained from the other carnation lines, had carnation-like morphology without any evidence of hybridity by flow cytometry and RAPD analyses. The progenies confirmed as hybrids had intermediate characters of the parents with respect to leaf width and flower size, but they had a uniform flower color, reddish purple, which was different from that of either parent. Since the hybrids obtained in the present study have some profitable characters such as vigorous growth in summer time, upright robust stem, broad leaves and early flowering, they are expected to be used for the breeding of carnation which is suitable for growing under the Japanese climate.     

Effects of hybridization on the immunity of collared Ficedula albicollis and pied flycatchers F. hypoleuca, and their infection by haemosporidians

Because they are ubiquitous and typically reduce the fitness of hosts, parasites may play important roles in hybrid zone dynamics. Despite much work on herbivores and hybrid plants, the effect of parasites on the fitness of animal hybrids is poorly known. In an attempt to partly fill this gap, we examined the prevalence of avian haemosporidians Haemoproteus in a hybrid zone between collared Ficedula albicollis and pied flycatchers F. hypoleuca . 40 species-informative genetic markers allowed us to identify F1 hybrids, thus avoiding problems inherent in many studies that group hybrid genotypes. Furthermore, naturally occurring extra-pair paternity allowed us to test the immune responses of pure and hybrid nestlings to a novel antigen (phytohaemagglutinin) in a shared environment. In contrast to previous suggestions that animal hybrids may more often display resistance against parasites than plant hybrids, F1 hybrids exhibited prevalence of parasitism and immune responses that were intermediate between the two parental species. We also detected differences between the two parental species in their prevalence of infection, with the competitively dominant species (collared flycatcher) being less often infected by Haemoproteus . Overall, our results contribute to other recent data supporting the idea that the resistance of animals to parasites is variously and unpredictably affected by hybridization, and that there is a concordance in the general patterns observed in plants and animals. Haemosporidians in avian hybrids provide a useful system for investigating the interactions between hosts and parasites that characterize host contact zones.