AGE AND POLYPHYLETIC ORIGINS OF HYBRID AND SPONTANEOUS PARTHENOGENETIC CAMPELOMA (GASTROPODA: VIVIPARIDAE) FROM THE SOUTHEASTERN UNITED STATES

We used mtDNA sequence variation to assess the origin, age, and spatial patterns of sequence divergence of triploid hybrid and diploid spontaneous parthenogens from southeastern United States populations of the freshwater snail Campeloma. There was strong support for multiple origins of both parthenogens using likelihood-ratio tests, and we argue that parthenogens are recently derived from sexuals. Atlantic coastal populations of C. limum or C. floridense were the maternal ancestors of Gulf Coast triploid hybrids in the Florida Panhandle. Sequence divergence within monophyletic groups of both parthenogens is similar to within-population divergence found in sympatric sexuals, and monophyletic clades of hybrid and spontaneous parthenogens are geographically widespread throughout the Atlantic and Gulf Coast rivers. These patterns are consistent with higher dispersal rates and recent range expansion of parthenogens, which should reduce the effects of mutation accumulation or parasitism. Range expansion may have occurred through interdrainage transfer during Pleistocene glacial periods.     

Speciation through androgenesis in the stick insect genus Clonopsis (Insecta Phasmatodea)

In Morocco, Clonopsis stick insects showed tangled reproductive interactions actually resulting into a network of phylogenetic relationships known as ‘reticulate evolution’. Peculiar to parthenogenetic C. gallica and C. soumiae (54 and 72 chromosomes, respectively) – closely related to the bisexual C. felicitatis (2n = 36) – is the finding of numerically polyploid karyotypes with a diploid structure. Androgenesis appeared to be the most parsimonious explanation accounting for both the low mitochondrial differentiation and the quick onset of those polyploids with structurally diploid karyotypes, paired with neat nuclear differentiations. According to a proposed model, hybrid triploid females would segregate balanced haploid and diploid 2nd oocytes immediately producing all kinds of parthenogens and androgens. Owing to these peculiar reproductive issues, we felt useful searching for stronger evidence by deeply analysing the mitochondrial genome. This new analysis showed a neat separation of sexual Tetouan haplotypes from the parthenogenetic and androgenetic ones, which are grouped in two slightly overlapping groups by network analysis: Moroccan parthenogens and androgens vs European C. gallica. It could be also envisaged that C. gallica has multiple origins, being a complex of parthenogenetic strains originated through independent hybridizations. The straightforward mechanism originating both triploid and tetraploid parthenogens well fits with both their widely ascertained low mitochondrial differentiation and the geographical closeness of the most similar samples, independently from their specific karyotype. Combining the outcomes of the hybridization events and androgenesis, which completely substitutes hybrid genomes with those of a related paternal species, would conceivably realize the observed picture of species structure and distribution. Owing to the reinforced data set, it now appears much more sensible to support androgenesis as a quick pathway to originate polyploids with numerically and genetically sharply differing chromosome sets, while maintaining, at the same time, high mitochondrial similarity.     

Cytogenetic studies in the Andropogon gayanus—A. tectorum complex (Graminae)

Cytogenetic studies in the Andropogon gayanus—A. tectorum complex (Granimae). Studies on the morphology, karyotype and meiotic behaviour of collections of Andropogon gayanus [2 n = 40), A. tectorum (2 n = 20,30) and their hybrids, obtained by both open pollination and controlled crosses, have been made. The chromosome number of 2 n = 30 for A. tectorum is new. Karyotypic analyses of the species and the preponderance of trivalents at diakinesis in the triploid and aneuploid hybrids show that considerable homology exists between the genomes of the two species. The evolutionary relationship between the two species and the probable origin of tetraploid A. gayanus are discussed.     

Contrasting reproductive strategies of triploid hybrid males in vertebrate mating systems

The scarcity of parthenogenetic vertebrates is often attributed to their ‘inferior’ mode of clonal reproduction, which restricts them to self‐reproduce their own genotype lineage and leaves little evolutionary potential with regard to speciation and evolution of sexual reproduction. Here, we show that for some taxa, such uniformity does not hold. Using hybridogenetic water frogs (Pelophylax esculentus) as a model system, we demonstrate that triploid hybrid males from two geographic regions exhibit very different reproductive modes. With an integrative data set combining field studies, crossing experiments, flow cytometry and microsatellite analyses, we found that triploid hybrids from Central Europe are rare, occur in male sex only and form diploid gametes of a single clonal lineage. In contrast, triploid hybrids from north‐western Europe are widespread, occur in both sexes and produce recombined haploid gametes. These differences translate into contrasting reproductive roles between regions. In Central Europe, triploid hybrid males sexually parasitize diploid hybrids and just perpetuate their own genotype – which is the usual pattern in parthenogens. In north‐western Europe, on the other hand, the triploid males are gamete donors for diploid hybrids, thereby stabilizing the mixed 2n‐3n hybrid populations. By demonstrating these contrasting roles in male reproduction, we draw attention to a new significant evolutionary potential for animals with nonsexual reproduction, namely reproductive plasticity.     

鲤鱼杂种优势多代利用的探讨

作者根据自己的工作和当前国内外有关研究工作的进展情况,提出了通过人工诱发杂种三倍体,并用雌核发育的方式繁衍后代的途径,以防止鲤鱼品种间杂交后代分离,从而达到杂种优势多代利用的设想。       

13/17罗伯逊易位猪POU1F1基因多态性

采用外周血淋巴细胞培养制备染色体标本, 对13/17罗伯逊易位猪的3种杂交组合的394头后代进行核型分析, 出现3种核型猪：13/17易位纯合子猪[2n=36, XY或XX, rob(13;17)]、13/17易位杂合子猪[2n=37, XY或XX, rob(13;17)]和正常核型猪[2n=38, XY或XX]。应用PCR-RFLP技术在POU1F1基因的1 746 bp扩增片段中检测到1个RsaⅠ限制性内切酶的多态位点。应用PCR-SSCP技术检测POU1F1基因第4外显子, 在3种杂交后代群中均未检测到突变。遗传多态性分析结果表明：RsaⅠ酶切多态位点的突变在3种杂交后代群中A等位基因和AA基因型频率占优势, 在3种核型群体中也是A等位基因和AA基因型频率占优势, 其中AB基因型频率在易位杂合型群体中较高。各杂交后代群均未达到Hardy-Weinberg平衡, 不同核型群亦处于非平衡状态。13/17易位杂合子猪×13/17易位杂合子猪和13/17易位杂合子猪×约克两杂交后代群的PIC表现为中度多态, 而13/17易位杂合子猪×皮杜杂交后代群表现为低度多态; 易位杂合型群体表现为中度多态, 正常核型和易位纯合型群体表现低度多态性。     

Clonal diversity and polyphyletic origins of hybrid and spontaneous parthenogenetic Campeloma (Gastropoda: Viviparidae) from the south-eastern United States

Some theories for the maintenance of sexual reproduction indicate that parthenogens may persist if there is high clonal diversity and high dispersal rates. Using allozymic variation, we report on the origin, clonal diversity and population structure of hybrid and spontaneous parthenogens from south-eastern United States populations of the freshwater snail Campeloma. Independent origins of triploid hybrid parthenogens in the Florida panhandle occurred by hybridization between an Atlantic coastal species (C. limum or C. floridense) and the Florida sexual species (C. geniculum). Allozyme genotypic diversity is similar between these hybrid parthenogens and sexuals. Diploid spontaneous parthenogens originated multiple times from nonlocal C.limum sexual populations in Atlantic coastal rivers, and levels of genotypic diversity are significantly higher in sexual C. limum. How parthenogens originate, the degree of clonal diversity, and their subsequent dispersal influence whether basic assumptions of evolution-of-sex models are met.     

Karyotype,sex determination and male meiosis in three benthic water bugs (Hemiptera: Nepomorpha: Aphelocheiridae)

We report here the first chromosome numbers for benthic water bugs (Nepomorpha: Aphelocheiridae). All three studied species, Aphelocheirus aestivalis (Fabricius, 1794), A. murcius Nieser and Millán, 1989 and Aphelocheirus sp. from Ebro River (northern Spain), have karyotype 2n = 22 + XX/X(0) and inverted sequence of the X chromosome divisions in male meiosis. The similarity and difference in cytogenetic traits between Aphelocheiridae and other families of Nepomorpha are shortly discussed.     

Physiological implications of genomic state in parthenogenetic lizards of reciprocal hybrid origin

Parthenogenesis often evolves in association with hybridization, but the associated ecological consequences are poorly understood. The Australian gecko Heteronotia binoei is unusual because triploid parthenogenesis evolved through reciprocal crosses between two sexual lineages, resulting in four possible cytonuclear genotypes. In this species complex, we compared the performance of these parthenogenetic genotypes with their sexual progenitors for a suite of physiological traits (metabolic rate, thermal tolerance, locomotor performance, and in vitro activity and gene sequence divergence of a cytonuclear metabolic pathway, cytochrome C oxidase). Mass‐specific metabolic rate scaled differently with body mass for parthenogens and sexuals, while heat tolerance provided the only evidence for cytonuclear incompatibility in hybrid parthenogens. The most prominent phenotypic effects were attributable to nuclear genome dosage. Overall, our results suggest that the hybrid/polyploidy origin of parthenogenetic H. binoei has had surprisingly few negative fitness consequences and may have produced a broader overall niche for the species.     

Mode of origin differentially influences the fitness of parthenogenetic freshwater snails

How parthenogenetic lineages arise from sexual ancestors may strongly influence their persistence over evolutionary time. Hybrid parthenogens often have elevated heterozygosity and ploidy, thus making it difficult to disentangle the influence of reproductive mode, hybridity and ploidy on their relative fitness. By comparing the relative fitness of both hybrid and non-hybrid parthenogens to their sexual ancestors, further insight may be gained into how these three factors influence the maintenance of sexual and parthenogenetic reproduction. In the present study, hybrid and non-hybrid parthenogenetic and sexual snails (Campeloma sp.) were compared for the following characteristics: female size-fecundity curves, offspring size, survivorship, and growth. Compared to nearby sexual populations, triploid hybrid parthenogens from the Florida Gulf coast have similar fecundity and offspring size, five-times higher survivorship, and 60% higher growth. Relative to nearby sexual populations, non-hybrid parthenogenetic C. limum from the Atlantic coast have significantly higher fecundity, smaller offspring size, similar survivorship and slightly lower growth. Given the considerable fitness advantages of parthenogens, especially hybrid parthenogens, it is enigmatic as to why these parthenogens occupy marginal natural habitats.     

Genetic and morphology analysis among the pentaploid F1 hybrid fishes (Schizothorax wangchiachii ♀ × Percocypris pingi ♂) and their parents

Triploid and pentaploid breeding is of great importance in agricultural production, but it is not always easy to obtain double ploidy parents. However, in fishes, chromosome ploidy is diversiform, which may provide natural parental resources for triploid and pentaploid breeding. Both tetraploid and hexaploid exist in Schizothorax fishes, which were thought to belong to different subfamilies with tetraploid Percocypris fishes in morphology, but they are sister genera in molecule. Fortunately, the pentaploid hybrid fishes have been successfully obtained by hybridization of Schizothorax wangchiachii (♀, 2n = 6X = 148) × Percocypris pingi (♂, 2n = 4X = 98). To understand the genetic and morphological difference among the hybrid fishes and their parents, four methods were used in this study: morphology, karyotype, red blood cell (RBC) DNA content determination and inter-simple sequence repeat (ISSR). In morphology, the hybrid fishes were steady, and between their parents with no obvious preference. The chromosome numbers of P. pingi have been reported as 2n = 4X = 98. In this study, the karyotype of S. wangchiachii was 2n = 6X = 148 = 36m + 34sm + 12st + 66t, while that the hybrid fishes was 2n = 5X = 123 = 39m + 28sm + 5st + 51t. Similarly, the RBC DNA content of the hybrid fishes was intermediate among their parents. In ISSR, the within-group genetic diversity of hybrid fishes was higher than that of their parents. Moreover, the genetic distance of hybrid fishes between P. pingi and S.wangchiachii was closely related to that of their parental ploidy, suggesting that parental genetic material stably coexisted in the hybrid fishes. This is the first report to show a stable pentaploid F₁ hybrids produced by hybridization of a hexaploid and a tetraploid in aquaculture.     

A karyological analysis of the artificial hybridization between Clarias gariepinus (Burchell, 1822) and Heterobranchus longifilis Valenciennes, 1840 (Pisces; Clariidae)

A karyological analysis of an artificial hybridization (reciprocal crosses) between two African clariid catfish, Clarias gariepinus (Burchell, 1822) and Heterobranchus longifilis Valenciennes, 1840, was performed. C. gariepinus has a standard karyotype of 2 n = 56, while H. longifilis has 2 n = 52. The hybrids revealed an intermediate karyotype (2 n = 54), and it appears as if they have totalized the haploid chromosome number of both parental species, excluding gynogenesis or androgenesis. The hybrid karyotype is considered as aneuploid, although the hybrids proved to be fertile. No variation was found in the hybrids karyotypes.     

Banded karyotype of spined loach Cobitis taenia and triploid Cobitis from Poland

The present work provides new data on the banding pattern of diploid Cobitis taenia and its triploid hybrid females, which belong to the diploid–polyploid complex in the Vistula River tributary. C-banding, silver-staining (Ag), and fluorescent staining with chromomycin A₃ techniques were used to describe the diploid and triploid karyotype. The karyotype of Cobitis taenia of 2n=48 was characterised by one pair of NOR-bearing subtelocentric chromosomes and at least four chromosomes with CMA₃-positive sites. The C-positive heterochromatin was present in the centromeres of almost all chromosomes and the pericentromeric regions of several metacentric and submetacentric chromosomes. The triploid females of 3n=74 had two pairs of chromosomes with active NORs. The NORs-sites were located terminally on two biarmed and two uniarmed chromosomes. The CMA₃-staining revealed at least six A₃-positive sites. The C-banded and A₃-stained triploid karyotype was composed of haploid set of Cobitis taenia and diploid set of unidentified species, so heterochromatin pattern confirmed the possibility of their hybrid origin. The characteristics of banded diploid and triploid karyotype, and the hypothetical karyotype of an unknown species of 2n=50 is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Karyotype evolution in the genus Boronia (Rutaceae)

New chromosome counts are reported for Boronia clavata 2 n  = 14, B. heterophylla 'Near White' 2 n  = 15, B.  'Carousel' 2 n  = 16, B. deanei 2 n  = 22, B. chartacea 2 n  = 32, B. keysii 2 n  = 32, B. pilosa 2 n  = 44, B. anethifolia 2 n  = 36 and B. citriodora 2 n  = 108. Studies in 20 genotypes of 18 species and one interspecific hybrid revealed that they are highly complex in terms of chromosome number, ploidy level, chromosomal length, karyotype constitution and asymmetry. Karyotype analysis indicated that Boronia taxa with high chromosome numbers are primitive and those with lower numbers are derived. The basic chromosome number for this genus is suggested to be x = 18. Analysis of chromosome number, variations of total chromosome length (TCL) and average chromosome length (ACL), Nombre Fondamental (NF) and karyotype asymmetry suggest that dysploid reduction is the major mechanism in Boronia karyotype evolution. Chromosomal rearrangements might also have been involved. Origin, chromosome number changes and spread of Boronia are discussed in relation to the species divergence and the geological and climatic changes of the Australian continent.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 309–320.     

ANDROGENETICS AND TRIPLOIDS FROM AN INTERACTING PARTHENOGENETIC HYBRID AND ITS ANCESTORS IN STICK INSECTS

Populations of unisexual organisms are often assumed to be genetically invariant (clones) and destined to a short existence on an evolutionary timescale. Unisexual organisms are most often obligate parthenogens and, by definition, ought to be completely isolated reproductively from related bisexual organisms. The assumption of complete reproductive isolation between amphimictic ancestors and thelytokous hybrids is common to most hypotheses on the evolution of sex and its adaptive significance. Stick insects of the genus Bacillus however provide evidence for reproductive interactions between allodiploid parthenogens and their ancestors, because pure species progeny (androgenetics) and triploid descendants are produced. These findings demonstrate that, through androgenesis, offspring of parthenogenetic hybrid females can contribute specimens of both sexes to the fathering species when fertilized by syntopic ancestral males and the parthenogenetic egg of strictly clonal females, when fertilized, allows a third genome to be added to the allodiploid chromosome set. These triploid genomes promote further genetic diversification and evolution of the unisexual populations through the formation of new clones by recombination during the changed maturation mode of allotriploid eggs. All this argues for much more complex breeding systems and evolutionary pathways than are usually assumed for hybrid unisexual organisms.     

Stability of the "two active X" phenotype in triploid somatic cells.

We examined triploid cells of XXY karyotype heterozygous for glucose 6 phosphate dehydrogenase (G6PD) electrophoretic variants with regard to the stability of their X chromosome phenotype. Clonal populations of cells derived from these human fibroblasts maintained a precise 1:2:1 ratio of A:heteropolymer:B isozymes throughout their life span, indicating stability of the two active X chromosomes in these cells. To determine the influence of the autosomal complement on X chromosome expression, we attempted to perturb the relationship. Fusion of these triploid cells with human diploid fibroblasts carrying a novel G6PD variant (B') resulted in heterokaryons exprssing a novel heteropolymer, presumably indicating that all three parental X chromosomes were active. However, no derepression of the inactive X chromosome was observed. Analysis of interspecific hybrids derived from triploid cells and mouse fibroblasts confirmed that activity of parental X chromosomes is maintained. Some human mouse hybrid clones, however, expressed only a single human G6PD isozyme, probably attributable to segregation of the pertinent X chromosome, but elimination of a relevant autosome cannot be excluded. The triploid cells transformed by SV40 showed alterations in LDH pattern and an approximately 10-20% decrease in chromosome number, but maintained the precise G6PD phenotype of the untransformed cell. These studies provide evidence for the stability of the X chromosome phenotype in triploid cells.     

A new allopatric lineage of the rodent Deltamys (Rodentia: Sigmodontinae) and the chromosomal evolution in Deltamys kempi and Deltamys sp

Deltamys Thomas 1917 is a poorly studied and rarely collected taxon of Akodontini (Sigmodontinae). The single described species, Deltamys kempi (DKE), has a basic karyotype with a diploid number of 2n = 37 in males and 2n = 38 in females, a fundamental number FN = 38 for both sexes, and an X(1)X(1)X(2)X(2)/X(1)X(2)Y sex determination system. Herein, a new allopatric form, Deltamys sp. (DSP), is reported, based on specimens from southern Brazil, with 2n = 40, FN = 40 and XX/XY sex chromosomes. We describe the karyotype and mechanism of chromosomal differentiation between both Deltamys complements. Phylogenetic analyses, based on the complete sequence (1,140 bp) of the mitochondrial cytochrome b gene, grouped Deltamys sp. as sister species to D. kempi, with up to 12% genetic divergence between them. The GTG-banding patterns show complete autosomal correspondence between D. kempi and Deltamys sp. and identify a tandem rearrangement involving DSP7, DSP19 and DKE4 that is responsible for the differences in 2n and FN. Chromosome painting with Akodon paranaensis chromosome 21 (a small metacentric akodont marker) paint revealed total homology with the smallest acrocentric Deltamys sp. chromosome, DSP19. This suggests the occurrence of a pericentric inversion or centromeric shift when compared to other akodontines, with a posterior tandem rearrangement giving rise to DKE4. In DKE, large blocks of pericentromeric constitutive heterochromatin are present on the autosomes and the X, and the Y/autosome has an entirely heterochromatic short arm. In DSP, small heterochromatic blocks are observed on autosomes and X, and the Y is a very small, mostly heterochromatic acrocentric. The cytogenetic analyses suggest that the Deltamys sp. karyotype is ancestral, with the derived condition resulting from a tandem fusion (DSP7 + DSP19) and the Y/autosome translocation giving rise to the multiple sex chromosome system. The autosomal rearrangements, the differences in CBG-banding patterns and Ag-NOR localization, as well as the presence of X(1)X(1)X(2)X(2)/X(1)X(2)Y and XX/XY sex determination mechanisms, possibly acting as a reproductive barrier, and the phylogenetic position within the Deltamys genus, with high genetic divergence, call for a taxonomic review of the genus.     

Karyotype differentiation in Chromaphyosemion killifishes (Cyprinodontiformes, Nothobranchiidae): patterns, mechanisms, and evolutionary implications

Chromaphyosemion killifishes are a karyotypically highly diverse group of small, sexually dimorphic fishes living in rainforest rivulets in tropical West and Central Africa. In the present study, we used various chromosome banding and staining techniques to analyse the karyotypes of 13 populations representing seven described species ( Chromaphyosemion loennbergii , Chromaphyosemion punctulatum , Chromaphyosemion splendopleure , Chromaphyosemion volcanum , Chromaphyosemion malumbresi , Chromaphyosemion melanogaster , Chromaphyosemion bitaeniatum ) and two undescribed forms ( Chromaphyosemion cf. lugens , Chromaphyosemion sp. Rio Muni GEMHS00/41). Diploid chromosome numbers (2 n ) and the number of chromosome arms (NF) ranged from 2 n  = 24 in C. malumbresi to 2 n  = 40 in C. bitaeniatum and from NF = 40 in C. volcanum and C. cf. lugens to NF = 54 in one population of C. loennbergii . A tentative XX/XY sex chromosome system was revealed in C. loennbergii , C. melanogaster , C. malumbresi , and Chromaphyosemion sp. Rio Muni GEMHS00/41. Mapping cytogenetic data for all described Chromaphyosemion species onto a recently published mitochondrial DNA phylogeny revealed a complex pattern of chromosomal evolution with several independent reductions of 2 n and independent modifications of NF and nucleolus organizer region phenotypes. Together with the results of preliminary crossing and mate choice experiments, the cytogenetic and molecular phylogenetic data suggest that, contrary to previous hypotheses, chromosomal rearrangements are probably not the most important and certainly not the only factor driving speciation in Chromaphyosemion killifishes.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 143–153.     

Regional localization of a beta-galactosidase locus on human chromosome 22.

Human white blood cells with an X/22 translocation [46, XX, t(X;22)(q23;q13)] were fused with Chinese hamster cells. The isolated hybrids were analyzed for human chromosomes and 21 enzyme markers. An electrophoretic technique for studying the beta-galactosidase isoenzymes in man-Chinese hamster hybrid cells was developed. Immunological studies showed that the beta-galactosidase marker studied in these hybrids did contain immunological determinants of human origin. Furthermore the results provided evidence that a locus for beta-galactosidase is situated on chromosome 22 distal to the breakpoint in q13.     

Studies on the Robertsonian chromosomal variation of Mus musculus domesticus (Rodentia, Muridae) in Greece

The karyotype of the house mouse, Mus musculus domesticus , was examined in 282 specimens from 44 localities, in an effort to gain better understanding of the Robertsonian (Rb) variation known to exist in Greece. We consider that an Rb system exists in Peloponnisos, southern Greece, distributed in an area that is substantially larger than previously known. It consists of at least three Rb races with 2 n  = 30, 2 n  = 24 and 2 n  = 28, respectively, the last being reported for the first time in this paper and carrying Rb(3.6), Rb(8.12), Rb(10.14), Rb(13.15), Rb(9.16) and Rb(11.17) in a homozygous state. Additional instances of variation in this Rb system include individuals with 2 n  = 31 and 32 of variable Rb constitution and hybrids between the Rb races with 2 n  = 30 and 2 n  = 24. In southern Peloponnisos, Rb(10.14) was found in either a homozygous or a heterozygous state (2 n  = 38 or 39). The relationships among the Rb populations of Peloponnisos are discussed and hypotheses for their evolution are proposed. Rb variation was also recorded in two new locations of eastern Sterea Ellas (2 n  = 28 and 29) and one in Ipiros, north-west Greece (2 n  = 38). These findings corroborate the existence of two separate Rb systems in those two areas. Moreover, among a number of islands surveyed, Rb variation was only found in Kythira island, with Rb(10.14) in a heterozygous state (2 n  = 39). Finally, the typical all-acrocentric karyotype (2 n  = 40) was found in 51 of the animals studied from 13 localities. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 503–513.