Morphological evidence for natural intergeneric hybridization in the New Zealand Gnaphalieae (Compositae): Anaphalioides bellidioides × Ewartia sinclairii

Wild intergeneric hybrids are recorded among six genera in the New Zealand Gnaphalieae, but little evidence substantiating their identity has been published. In this paper we evaluate the identity of putative hybrids between two species of Gnaphalieae endemic to New Zealand, Anaphalioides bellidioides and Ewartia sinclairii . The two species are occasionally sympatric in the north-east of the South Island and wild putative hybrids are rarely encountered. To test the hybridity hypothesis, specimens from nine putative hybrids were collected from one site and analysed for 76 morphological characters. The putative hybrids possessed predominantly intermediate or parental character states in comparison with A. bellidioides and E. sinclairii . Extreme traits were less common and a single novel character state was recorded in two hybrids only. Non-metric multidimensional scaling of dissimilarities derived from both continuous and discrete characters was strongly supportive of the hybridity hypothesis. Canonical discriminant analysis of the continuous characters was supportive for some putative hybrids only, in part reflecting the possession of extreme states in characters with high loadings. One of the putative hybrids was strongly indicated to be a backcross with A. bellidioides . The taxonomic treatment of cross-compatible genera is discussed.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 59−75.     

Distribution,biology and hybridization of Scaphirhynchus albus and S. platorynchus in the Missouri and Mississippi rivers

Synopsis Scaphirhynchus albus and S. platorynchus were studied in Missouri during 1978–1979 to assess their distribution and abundance, to obtain information on their life histories, and to identify existing or potential threats to their survival. S. platorynchus was collected in substantial numbers (4355 specimens) at all 12 sampling stations in the Missouri and Mississippi rivers, while only 11 S. albus were captured from 6 stations. Twelve specimens identified in the field as hybrids between the two species were captured from 4 stations. Morphometric and meristic comparisons of presumed hybrids with the parent species, using cluster and principal components analyses, demonstrated intermediacy of most specimens identified in the field as hybrids. Aquatic insects comprised most of the diet of S. platorynchus and S. albus, but S. albus and the hybrids had consumed considerable quantities of fish. S. albus grew more rapidly than S. platorynchus, while the growth of hybrids was intermediate. Hybridization appears to be a recent phenomenon, resulting from man-caused changes in the big-river environment. Hybridization may be a threat to survival of S. albus in the study streams.     

Morphologic comparisons of hatchery-reared specimens of Scaphirhynchus albus, Scaphirhynchus platorynchus, and S. albus × S. platorynchus hybrids (Acipenseriformes: Acipenseridae)

Extensive habitat modifications within the Mississippi and Missouri rivers have presumably interfered with the reproductive isolating mechanisms between the endangered pallid sturgeon, Scaphirhynchus albus, and the sympatric shovelnose sturgeon, Scaphirhynchus platorynchus, causing hybridization between these two species. Several character indices were developed to assist fisheries biologists in identifying specimens of S. albus, S. platorynchus, and their putative hybrids. The indices have numerous assumptions, including that pure strains of both parental species are within the sample analyzed and that hybrids are morphologically intermediate relative to their parents. If these indices have produced inaccurate identifications, then previous work on Scaphirhynchus studies in the Mississippi and Missouri rivers are questionable, including status surveys, captive propagation efforts, or the harvesting of tissues for genetic studies. In this study we tested indices by examining progeny of ‘known’ pallid, shovelnose, and hybrid sturgeon propagated, raised, and preserved at hatcheries. These 60 specimens [78–600 mm standard length (SL)] were propagated with breeding stock from the upper Missouri River drainage, where hybridization between these two species presumably does not occur. Existing indices did not correctly identify small (<250 mm SL) or a combination of small and large (>250 mm SL) sizes of S. albus, S. platorynchus, and their hybrids. Indices worked fairly well in identifying large S. platorynchus, but not in differentiating large S. albus from hybrids. We used principal components analysis (PCA) as an alternative approach to character indices. No a priori knowledge of the identity of the specimen is required with this multivariate technique, which avoids potential circular reasoning present in indices. We were able to completely or almost completely separate both sturgeon species and their hybrids by extracting principal components from a correlation matrix of 13 meristic characters in a standard PCA and extracting size‐corrected principal components from a covariance matrix of 51 morphometric variables using a sheared PCA. Additionally, we demonstrated that first generation hybrids were intermediate with respect to their parental species. Multivariate analyses with a reduced character set of six meristic and 12 morphometric variables also led to accurate and reliable specimen identification. Head spines and numerous qualitative characters are also extremely useful in differentiating between Scaphirhynchus species and their hybrids. In addition to all morphometric characters, some meristic characters and the degree of head spine fusion vary significantly with SL of sturgeons. Recording appropriate data from released specimens, including photovouchers, and making this information available is essential for researchers to have any scientific or legal basis for genetic or any other studies involving these sturgeons.     

Molecular evidence for hybridization in Colias (Lepidoptera: Pieridae): are Colias hybrids really hybrids?

Gene flow and hybridization among species dramatically affect our understanding of the species as a biological unit, species relationships, and species adaptations. In North American Colias eurytheme and Colias eriphyle, there has been historical debate over the extent of hybridization occurring and the identity of phenotypically intermediate individuals as genetic hybrids. This study assesses the population structure of these two species to measure the extent of hybridization and the genetic identity of phenotypic intermediates as hybrids. Amplified fragment length polymorphism (AFLP) marker analysis was performed on 378 specimens collected from northern California and Nevada. Population structure was inferred using a Bayesian/Markov chain Monte Carlo method, which probabilistically assigns individuals to genetic clusters. Three genetic clusters provided the best fit for the data. C. eurytheme individuals were primarily assigned to two closely related clusters, and C. eriphyle individuals were mostly assigned to a third, more distantly related cluster. There appeared to be significant hybridization between the two species. Individuals of intermediate phenotype (putative hybrids) were found to be genetically indistinguishable from C. eriphyle, indicating that previous work based on the assumption that these intermediate forms are hybrids may warrant reconsideration.     

Intermediate filament expression and lifespan potential in human somatic cell hybrids

Summary Limited lifespan human diploid fibroblast cells have been fused with the HeLa derived cell line HEB 7A which possesses transformed growth characteristics and unlimited division potential. HEB 7A expresses keratin intermediate filaments, while the fibroblast cells express only vimentin intermediate filaments. Independently arising clones of hybrids were examined for the presence of keratin by indirect immunofluorescence. Of 11 limited lifespan hybrids, all were keratin negative and possessed the growth characteristics of the fibroblast parent. Of 8 transformed hybrids, 6 arising early after fusion and 2 arising late, all were keratin-positive and simultaneously expressed the transformed growth characteristics of loss of density dependent growth inhibition, low serum dependence, and anchorage independence. It is concluded that the growth properties of these hybrids are associated with the type of intermediate filament expressed. The intermediate filament expression is therefore a marker of proliferative potential in these hybrids. This work was supported by grant no. AG 02664 from NIA (to C.L.B.) and by grant nos. 1R01 HD 18129-01 from NIH and PCM83-09068 from NSF (to R.H.S.). Editor’s Statement The tight correlation between the expression of the intermediate filaments of the immortal parent in hybrids of limited lifespan fibroblasts and HeLa cells with the transformed phenotype is of interest. It may offer important clues to the mechanism involved in cellular senescence. Gordon H. Sato     

Hybridization between tetraploid species of Alopecurus L. (Poaceae): morphological studies of natural and artificial hybrids

The morphology of individuals of mixed natural populations of three species of Alopecurus, A. pratensis, A. geniculars and A. arundinaceus , is described. It is suggested that plants morphologically intermediate between the parental species are hybrids or of hybrid origin. Hybridization occurs more readily between A. pratensis and A. arundinaceus than between A. pratensis and A. geniculate , since intermediate forms were recovered from all mixed populations of A. pratensis and A. arundinaceus. The intermediate forms occur only in a few populations of A. pratensis and A. geniculars where an appropriate habitat is available. Evidence of backcrossing and therefore introgression comes from the continuum of intermediate forms that exists between the species. Scatter diagrams for individual populations show distinct differences in the degree of introgression. Observations on artificially produced hybrids are similar to those on naturally occurring hybrids.     

Natural hybridization does not dissolve species boundaries in commercially important sea cucumbers

The study of species boundaries in areas of sympatry provides important insight into speciation processes. We investigated whether (i) two sympatric holothurians, Holothuria scabra and H. s. var. versicolor constituted species, and (ii) specimens of intermediate phenotype hybrids. Results from allozyme and 16S mtDNA sequence analyses indicated these two sea cucumbers to be distinct but young biological and phylogenetic species. Several private allozyme alleles existed and a Bayesian analysis grouped varieties into separate clusters. MtDNA sequences hardly varied within each taxon, and nine single bp changes were diagnostic between these two taxa. Allozyme allele frequencies in individuals of intermediate phenotype were intermediate to those of H. scabra and H. s.  var.  versicolor , most private alleles were present and heterozygote frequencies were higher than in either species. Ancestry coefficients modelled for these individuals were close to 0.5, indicating that the two taxa contributed equally to their genome. MtDNA sequences were identical to those of either species. We conclude that individuals of intermediate phenotype represent F1 hybrids. The presence of hybrids demonstrates that the opportunity for introgression exists, but is not realized, as backcrossing and introgression were not supported by the data. Thus, the genetic integrity of either holothurian species remains intact through an unknown postzygotic mechanism, possibly hybrid sterility.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 261–270.     

The colour pattern of the caudal fin, a useful criterion for identification of two species of Tilapia and their hybrids

The present work reports on some chromatic characters and their change with size in two species of Tilapia ( T. zillii and T. guineensis ) and their first generation hybrids. Successful reciprocal hybridizations between T. zillii and T. guineensis were performed in concrete tanks. The hybrids obtained were viable. The colour patterns of the hybrids and their parents were registered during a rearing cycle of 12 months. Between 2 and 13 cm standard length ( L _S), the hybrids were found to be heterogeneous and three phenotypes were observed. The type (1) phenotype had a fully yellowish caudal fin without dots, the type (2) phenotype had a bicoloured caudal fin with the upper part clear yellowish and the lower part dark yellowish and without dots and the type (3) had a similar bicoloured caudal fin, but with dots. Above 13 cm L _S, the hybrid population was homogenous and all specimens had a bicoloured caudal fin with dots. In T. zillii , all specimens >14 cm L _S had a greyish caudal fin with dots while all T. guineensis >13 cm L _S were characterized by a bicoloured caudal fin without dots. A multivariate analysis of the morphometric and meristic characters did not allow a clear separation of all groups. The study showed that the external morphology of the hybrids was intermediate to that of the parental species.     

Enrichment of heterokaryocytes between mesophyll and epidermis protoplasts by density gradient centrifugation after electric fusion

Summary Mesophyll protoplasts from Nicotiana glauca were fused with epidermal protoplasts from N. langsdorffii by an electric pulse. After the fusion products were centrifuged on stepwise density gradient centrifugation using Percoll and sea water, somatic hybrids were observed at 70%–80% in the fraction recovered from the intermediate specific gravity fraction between epidermis and mesophyll protoplasts. From offsprings of these somatic hybrids, teratomatous plants were regenerated. Since the difference of specific gravity between mesophyll and epidermis protoplasts is inherent, this procedure can be essentially applied to obtain somatic hybrids between any combination of plants. The significance of this study is discussed in relation to obtaining somatic hybrids between plant materials without any appropriate genetic markers.     

Natural and sexual selection against hybrid flycatchers

While sexual selection is generally assumed to quickly cause or strengthen prezygotic barriers between sister species, its role in causing postzygotic isolation, through the unattractiveness of intermediate hybrids, is less often examined. Combining 24 years of pedigree data and recently developed species-specific molecular markers from collared (Ficedula albicollis) and pied (Ficedula hypoleuca) flycatchers and their hybrids, we were able to quantify all key components of fitness. To disentangle the relative role of natural and sexual selection acting on F1 hybrid flycatchers, we estimated various fitness components, which when combined represent the total lifetime reproductive success of F1 hybrids, and then compared the different fitness components of F1 hybrids to that of collared flycatchers. Female hybrid flycatchers are sterile, with natural selection being the selective force involved, but male hybrids mainly experienced a reduction in fitness through sexual selection (decreased pairing success and increased rate of being cuckolded). To disentangle the role of sexual selection against male hybrids from a possible effect of genetic incompatibility (on the rate of being cuckolded), we compared male hybrids with pure-bred males expressing intermediate plumage characters. Given that sexual selection against male hybrids is a result of their intermediate plumage, we expect these two groups of males to have a similar fitness reduction. Alternatively, hybrids have reduced fitness owing to genetic incompatibility, in which case their fitness should be lower than that of the intermediate pure-bred males. We conclude that sexual selection against male hybrids accounts for approximately 75% of the reduction in their fitness. We discuss how natural and sexual selection against hybrids may have different implications for speciation and conclude that reinforcement of reproductive barriers may be more likely when there is sexual selection against hybrids.     

尖音库蚊复合组杂交子一代4龄幼虫形态性状的研究

对我国尖音库蚊复合组（Culex pipiens complex）中的尖音库蚊Cx. Pipiens pipiens、淡色库蚊Cx. Pipiens pallens和致倦库蚊Cx. Pipiens quinquefasciatus之间杂交的F₁代幼虫形态进行了方差和典型变量分析,结果发现杂交组F₁代4龄幼虫在呼吸管指数、1-S第1对毛和第2对毛的分枝数3个性状上与亲本有明显的差异,而且介于两亲本之间。     

Electrophoretic identity between allis shad, Alosa alosa (L.), and twaite shad, A.fallax (Lacépède)

Morphological characteristics as well as electrophoretic polymorphism have been analysed in eight samples of allis shad, Alosa alosa (L.) and twaite shad, Alosa fallax (Lacepede), collected in the Loire basin and the Gironde-Dordogne system. The morphological characteristics showed that allis and twaite shad were present in these samples. Moreover, specimens with intermediate characteristics were found in the Loire and assumed to be hybrids between the two forms. By contrast, the two species were monomorphic and electrophoretically indistingishable at the 22 loci analysed. Therefore, it cannot be excluded that these two forms correspond to a single species.     

Field studies reveal strong postmating isolation between ecologically divergent butterfly populations

Gene flow between populations that are adapting to distinct environments may be restricted if hybrids inherit maladaptive, intermediate phenotypes. This phenomenon, called extrinsic postzygotic isolation (EPI), is thought to play a critical role in the early stages of speciation. However, despite its intuitive appeal, we know surprisingly little about the strength and prevalence of EPI in nature, and even less about the specific phenotypes that tend to cause problems for hybrids. In this study, we searched for EPI among allopatric populations of the butterfly Euphydryas editha that have specialized on alternative host plants. These populations recall a situation thought typical of the very early stages of speciation. They lack consistent host-associated genetic differentiation at random nuclear loci and show no signs of reproductive incompatibility in the laboratory. However, they do differ consistently in diverse host-related traits. For each of these traits, we first asked whether hybrids between populations that use different hosts (different-host hybrids) were intermediate to parental populations and to hybrids between populations that use the same host (same-host hybrids). We then conducted field experiments to estimate the effects of intermediacy on fitness in nature. Our results revealed strong EPI under field conditions. Different-host hybrids exhibited an array of intermediate traits that were significantly maladaptive, including four behaviors. Intermediate foraging height slowed the growth of larvae, while intermediate oviposition preference, oviposition site height, and clutch size severely reduced the growth and survival of the offspring of adult females. We used our empirical data to construct a fitness surface on which different-host hybrids can be seen to fall in an adaptive valley between two peaks occupied by same-host hybrids. These findings demonstrate how ecological selection against hybrids can create a strong barrier to gene flow at the early stages of adaptive divergence.     

Morphological and molecular evidence for natural hybridization in sympatric population of Roscoea humeana and R. cautleoides (Zingiberaceae)

The sympatric occurrence of some species in Roscoea is very common, but little information is available on natural hybridization. However, some intermediate individuals were found on the sympatric population of Roscoea humeana and R. cautleoides at Ganhaizi population in northwestern Yunnan Province, China. We suspected that these intermediate individuals were the hybrids of R. humeana and R. cautleoides from the previous evidence, but could not confirm them. In this study, morphometric analysis was followed by examination of HAT-RAPD polymorphisms to determine the occurrence of natural hybridization between sympatric R. humeana and R. cautleoides. The results showed that most morphological characters of the putative hybrids were found to be intermediate between those of R. humeana and R. cautleoides. Meanwhile, molecular analysis confirmed that the morphological intermediates were derived from hybridization between the two species. From the analysis of the NewHybrids, the hybridization individuals were mainly F(1)s. These results indicated that interspecific hybridization between R. humeana and R. cautleoides indeed occurred in sympatric population.     

Morphological and molecular identification of Prosapia simulans (Walker) (Hemiptera: Cercopidae), and screening and mechanisms of resistance to this spittlebug in Brachiaria hybrids

Prosapia simulans (Walker) is an important spittlebug species that attacks forage grasses of the genus Brachiaria (Trin.) Griseb. from Mexico to Colombia. This, and several other species of spittlebugs, cause important economic losses to the livestock production industry. Development of resistant cultivars is regarded as the best method of control. In the present study we used taxonomic keys, dissection of male genitalia and RAPD-PCR patterns to reconfirm the identity of P. simulans specimens collected in Colombia and Mexico. We were able to reconfirm that P. simulans occurs as a pest of Brachiaria from Mexico to Colombia. We also studied the levels and mechanisms of resistance present in 34 Brachiaria hybrids developed by CIAT. Infestations were made with six eggs per plant. We used 10 replications (plants) per genotype in a completely randomized design. Seven hybrids were found to be susceptible, 16 showed intermediate resistance and 11 were resistant. Antibiosis was the mechanism of resistance expressed in resistant hybrids as well as in the resistant checks CIAT 6294 and CIAT 36062. Tolerance was absent. The genotypes BRX 4402 and CIAT 0606 were classified as highly susceptible.     

Ploidy levels in silverside fishes (Atherinidae, Menidia) on the Texas coast: flow-cytometric analysis of the occurrence of allotriploidy

Flow cytometry of nuclear DNA fluorescence in erythrocytes, coupled with gene dosage assessments derived from electrophoresis of proteins, reaffirmed that the Menidia clarkhubbsi complex of unisexual atherinid fishes is diploid. Non-recombinant hybrids between M. beryllina and M. peninsulae represented 18% (108 specimens) of the Menidia collected from three pools in the Copano Bay area and 9-6% (42 specimens) of those from a pool on Galveston Island. Of those hybrids, 35 and 5%, respectively, were triploids. Zymograms indicated that the triploids either had two doses of genes from M. beryllina and one from M. peninsulas or they had one from the former species and two from the latter. The hybrids seem to be maintained primarily, if not entirely, by ongoing hybridization and back-crossing of F₁ hybrids to the parental species. Triploids apparently result from the combination of unreduced, diploid gametes from F₁ hybrids with haploid gametes from either M. beryllina or M. peninsulae.     

Interspecific hybridization in wild roses (<Emphasis Type="Italic">Rosa</Emphasis> L. sect. Caninae DC.)

Variability of morphological characters and Inter Simple Sequence Repeat (ISSR) markers is studied in a mixed multispecies sympatric growth of wild roses in Lugansk province of Ukraine. Several methods of data analysis are used, such as Principal Coordinates Analysis, cluster analysis (UPGMA), and Bayesian analyses of population structure with the Structure 2.2 and NewHybrids programs. The results indicate that there are four species growing at the site, viz. R. canina, R. villosa, R. dimorpha, and R. podolica, as well as various hybrids between them. The hybrid nature of the specimens is confirmed by molecular data, however they are not intermediate between the parental species as to their morphology. The hybrids either coincide morphologically with one of the parents, or demonstrate novel combinations of diagnostic characters.     

Slug herbivory on hybrids of the crop Brassica napus and its wild relative B. rapa

Some plant species can cross with each other but stay nevertheless distinct with little gene flow between them. Selective herbivory could explain this pattern when hybrids are more susceptible or intermediate between their parents. We performed choice and no-choice experiments with the slug Arion lusitanicus to test this hypothesis for the crop Brassica napus, wild B. rapa and their backcross hybrids. In both experiments slugs greatly preferred B. napus over B. rapa while average herbivory on backcross hybrids was intermediate. Concentrations of aliphatic glucosinolates in the hybrids were intermediate between the parental species. Slug herbivory potentially reduces establishment of backcross hybrids. This hypothesis needs to be tested in the field.     

四倍体大燕麦×六倍体裸燕麦的杂种F1的产生及鉴定

本研究以四倍体大燕麦 (AvenamagnaL .)做母本 ,六倍体裸燕麦 (AvenanudaL .)做父本进行杂交 ,利用幼胚拯救技术获得了杂种F1,并对其后代形态特征进行了观察 ;对杂种F1同工酶图谱和DNA指纹图谱进行了分析。杂种F1形态特征偏亲本或介于双亲之间 ;同工酶研究表明多数F1具有双亲互补酶带 ;RAPD分析不同引物扩增产物F1呈共显性或偏父、偏母。这些结果表明F1为真杂种     

四倍体大燕麦×六倍体裸燕麦的杂种F1的产生及鉴定

本研究以四倍体大燕麦（Avena magna L.）做母本,六倍体裸燕麦（Avena nuda L.）做父本进行杂交,利用幼胚拯救技术获得了杂种F1,并对其后代形态特征进行了观察;对杂种F1同工酶图谱和DNA指纹图谱进行了分析。杂种F1形态特征偏亲本或介于双亲之间;同工酶研究表明多数F1具有双亲互补酶带;RAPD分析不同引物扩增产物F1呈共显性或偏父、偏母。这些结果表明F1为真杂种。