二倍体鲫鲤F2产生不同倍性卵子的证据

在检测到鲫鲤F2产生3种不同大小(直径分别为0.13 cm,0.17cm和0.2 cm)类型的卵子基础上,进行了F2(♀)×红鲫(♂)及F2(♀)×四倍体鲫鲤(♂)的交配实验.通过染色体计数和流式细胞仪分析,在F2(♀)×红鲫(♂)后代中获得了四倍体、三倍体、二倍体鱼;在F2(♀)×四倍体鲫鲤(♂)后代中获得了四倍体和三倍体鱼.这两个交配组合后代中出现的不同倍性的鱼类为证明鲫鲤F2能产生三倍体、二倍体和单倍体卵子提供了进一步证据.F2(♀)×红鲫(♂)中雄性四倍体鱼的存在说明在四倍体后代中存在基因型为XXXY的个体.对上述两个交配组合后代的四倍体鱼和三倍体鱼的性腺结构观察表明四倍体鱼是可育的,而三倍体鱼是不育的.作者认为鲫鲤F2能够产生二倍体和三倍体卵子与核内复制机制和生殖细胞的融合有关.     

DNA ploidy-level variation in native and invasive populations of Lythrum salicaria at a large geographical scale

Aim  This study aimed to document precisely the patterns of DNA ploidy variation in the native and secondary ranges of Lythrum salicaria distribution. The hypothesis that species invasiveness had been induced by a switch in ploidy level was addressed.
Location  Europe, Middle East, North America.
Methods  DNA ploidy levels of 1884 progenies of 578+ plants collected at 124 localities were determined by DAPI flow cytometry.
Results  Large cytotype variation (2 x , 3 x , 4 x and 6 x ) was found across the native area of distribution (64 populations covering 12 European and two Middle Eastern countries). DNA hexaploids were detected for the first time, and rare DNA triploids were reliably confirmed. DNA tetraploids largely prevailed across the native range studied, while DNA diploids and DNA hexaploids were recorded only in Israel and Turkey, respectively. DNA triploid progenies occurred in one population from Hungary (together with DNA tetraploids). Sympatric growth of DNA tetraploids and DNA hexaploids was repeatedly encountered in Turkey. In contrast, cytotype uniformity was a typical feature of the invasive North American plants. Sixty populations, covering 13 states of the USA and provinces of Canada, were characterized by the presence of only DNA tetraploids.
Main conclusions  Several L. salicaria cytotypes (2 x , 3 x , 4 x , 6 x ) occur in the native range of distribution, with much variation concentrated in the Middle Eastern countries, whereas only DNA tetraploids appeared to occur in North America. Our data show that the invasive spread of North American populations was not triggered by differences in ploidy level. Alternative explanations should be sought.     

Global analysis of the small RNA transcriptome in different ploidies and genomic combinations of a vertebrate complex--the Squalius alburnoides

The Squalius alburnoides complex (Steindachner) is one of the most intricate hybrid polyploid systems known in vertebrates. In this complex, the constant switch of the genome composition in consecutive generations, very frequently involving a change on the ploidy level, promotes repetitive situations of potential genomic shock. Previously in this complex, it was showed that in response to the increase in genome dosage, triploids hybrids could regulate gene expression to a diploid state. In this work we compared the small RNA profiles in the different genomic compositions interacting in the complex in order to explore the miRNA involvement in gene expression regulation of triploids. Using high-throughput arrays and sequencing technologies we were able to verify that diploid and triploid hybrids shared most of their sequences and their miRNA expression profiles were high correlated. However, an overall view indicates an up-regulation of several miRNAs in triploids and a global miRNA expression in triploids higher than the predicted from an additive model. Those results point to a participation of miRNAs in the cellular functional stability needed when the ploidy change.     

First evidence of autotriploidization in sterlet (Acipenser ruthenus)

Polyploidization has played an important role in vertebrate evolution. Acipenseridae bring clear examples of polyploidy ancestry and, also, polyploidization seems to be an ongoing process in these fishes. In the present study, the genetic origin of six triploid specimens morphologically determined as Acipenser ruthenus from commercial aquaculture was analyzed using a combination of mitochondrial and nuclear markers. A further five successive statistical analyses including median joining of mitochondrial DNA control region sequences, principal coordinate analysis (PCA), factorial correspondence analysis (FCA), STRUCTURE assignation, and NewHybrids status determination for microsatellite data were applied for the clarification of the origin of one extra chromosome set added in these triploids genomes. Although interspecific hybridization had been suggested as a source of these triploids, the statistical analyses showed that the investigated triploids originate from autotriploidization rather than from interspecific hybridization. Therefore, we conclude that a combination of molecular markers with suitable statistical analyses should be used to verify the origin of unusual ploidy level. Evidently, such an approach is critically essential in aquaculture, where interspecific hybridization is very common and usually detected by changes in ploidy levels only.     

Genetic screening of farmed Atlantic salmon escapees demonstrates that triploid fish display reduced migration to freshwater

Each year, hundreds of thousands of farmed Atlantic salmon escape from fish farms into the wild. Some of these escapees enter freshwater, and manage to interbreed with native populations. To hinder further genetic introgression in native populations, the use of sterile triploid salmon within commercial aquaculture is being examined. However, if triploid escapees migrate into freshwater, they may still have ecological impacts on local populations. In the present study, we used microsatellite DNA genotyping to determine the ploidy of 3794 farmed escapees captured in 17 Norwegian rivers in the period 2007–2014. Although a previous study has reported an average of 2 % triploids in Norwegian fish farms during this exact period, here, we only observed 7 (0.18 %) triploids among the escapees captured in freshwater. In addition, we identified three trisomic escapees. For the triploids where the within-river capture location was determined, they were only observed in the lower reaches and not on the spawning grounds. It is concluded that propensity for triploid Atlantic salmon to migrate into freshwater following escape from a fish farm is significantly lower than for normal diploid salmon escapees. Therefore, commercial production of triploids should not only be seen as an effective way of stopping genetic introgression, it will also significantly reduce the numbers of escapees entering rivers, which in turn limits ecological interactions and potential disease transmission.     

Genesis of microspore-derived triploid petunias

Summary A total of 61 microspore-derived plants of Petunia parodii were grown to maturity revealing a predominent population of triploids, 80.3%. Cytological investigations, together with the evidence from microfluorimetry, suggest that the origin of these triploids was due to the fusion of interphase nuclei in two different pathways. In the majority of embryogenic microspores, a vegetative nucleus of 1C DNA content fused with an endo-reduplicated 2C DNA generative nucleus at the binucleate stage and produced true triploid embryoids and plantlets (A pathway). Where this fusion failed, both the vegetative and the generative nuclei divided separately and in the multinucleate microspore two or more daughter nuclei fused to form a mixoploid embryoid. Such mixoploid embryoids produced a mixed population of plants with various ploidy levels as well as ploidy polymorphism within an individual. Since the triploids are morphologically superior with a faster growth rate than their diploids and related tetraploids, a predominent population of triploid plants was obtained from such mixoploid embryoids (B pathway). By low temperature treatment of the anther-donor buds, the embryogenic response of microspores was enhanced up to 5-fold.     

CYTOLOGICAL AND CHEMICAL VARIATION IN PITYROGRAMMA TRIANGULARIS

The cytology and chemistry of three populations of the species complex Pityrogramma triangularis from Santa Barbara County, California, were studied. The basic chromosome number of these ferns is x = 30, and there are diploids, triploids, and tetraploids. Although gross morphology in the plants is similar, four chemical types are observed when extracts of the external frond pigments are analyzed. Ten of the twelve possible combinations of ploidy level and pigment types have been found. Correlations of spore condition, cytology, and chemistry which indicate either an autotetraploid or allotetraploid derivation of the complex are discussed.     

Possible pathways of the gene flow inTaraxacum sect.Ruderalia

Reproductive behaviour and the pathways of gene flow among ploidy levels were studied experimentally inTaraxacum sect.Ruderalia. Diploid, triploid and tetraploid individuals were sampled from mixed diploid — polyploid natural populations. 136 experimental hybridizations between the plants of different ploidy levels were performed. Seeds resulting from these crosses, those obtained from isolated anthodia as well as from open pollinated anthodia (both from cultivated and wild plants) were subjected to the flow-cytometric seed screening (FCSS) to determine ploidy levels in the progeny and to infer breeding behaviour of maternal plants. Three possible pathways of the gene flow were studied: (A) fertilization of sexuals by pollen of apomicts, (B) B_III hybrid formation, (C) facultative apomixis. Diploid maternal plants when experimentally crossed with triploid pollen donors produced diploids and polyploid progeny, while when pollinated with a mixture of the pollen of diploids and triploids or insect pollinated, no polyploids were discovered. It seems that in the mixture with the pollen of diploids, the pollen of triploids is ineffective. Tetraploids produce hybrids much easier with diploid mothers and their role in wild populations requires further study. Triploid mothers, even those with subregular pollen did not show traces of facultative apomixis. B_III hybrids were present in the progeny of both triploids and tetraploids, in tetraploids in quite high percentages (up to 50% of the progeny in some crosses).     

Detection of individual ploidy levels with genotyping‐by‐sequencing (GBS) analysis

Ploidy levels sometimes vary among individuals or populations, particularly in plants. When such variation exists, accurate determination of cytotype can inform studies of ecology or trait variation and is required for population genetic analyses. Here, we propose and evaluate a statistical approach for distinguishing low‐level ploidy variants (e.g. diploids, triploids and tetraploids) based on genotyping‐by‐sequencing (GBS) data. The method infers cytotypes based on observed heterozygosity and the ratio of DNA sequences containing different alleles at thousands of heterozygous SNPs (i.e. allelic ratios). Whereas the method does not require prior information on ploidy, a reference set of samples with known ploidy can be included in the analysis if it is available. We explore the power and limitations of this method using simulated data sets and GBS data from natural populations of aspen (Populus tremuloides) known to include both diploid and triploid individuals. The proposed method was able to reliably discriminate among diploids, triploids and tetraploids in simulated data sets, and this was true for different levels of genetic diversity, inbreeding and population structure. Power and accuracy were minimally affected by low coverage (i.e. 2×), but did sometimes suffer when simulated mixtures of diploids, autotetraploids and allotetraploids were analysed. Cytotype assignments based on the proposed method closely matched those from previous microsatellite and flow cytometry data when applied to GBS data from aspen. An R package (gbs2ploidy) implementing the proposed method is available from CRAN.     

GENETICAL POPULATION STRUCTURE IN PLANTS: GENE FLOW BETWEEN DIPLOID SEXUAL AND TRIPLOID ASEXUAL DANDELIONS (TARAXACUM SECTION RUDERALIA)

Levels and distribution of genetic variation were studied in central and western European populations of Taraxacum section Ruderalia containing differing mixtures of sexual diploid and asexual triploid plants. All sexual populations were panmictic with their variation partitioned mainly among populations. Genotypic diversity in triploid samples was very high with few clones widespread and many clones restricted to one or a few populations. Extensive amounts of gene (pollen) flow between the diploid and triploid components of a population were inferred from the following data: (1) the two ploidy levels share all major allozyme polymorphisms; (2) the intrapopulational homogeneity in genic variation between diploids and triploids contrasts strongly with the geographic differentiation at each ploidy level separately; (3) population-unique alleles simultaneously occur at the two ploidy levels; (4) not only sexuals but also asexuals generally simulate Hardy-Weinberg expectations. Most likely, intrapopulational gene exchange occurs bidirectionally by mechanisms such as reductional pollen meiosis in apomictic plants, facultative apomixis, and formation of unreduced gametes in sexuals. Thus, diploid and triploid Taraxacum section Ruderalia are less genetically isolated than has previously been supposed and probably form a cohesive evolutionary unit with the level at which gene pools are shared differing by population.     

Evidence of Different Ploidy Eggs Produced by Diploid F2 Hybrids of Carassius auratus (♀) × Cyprinus carpio (♂)

Based on the presence of three types of eggs with different diameters 0.13, 0.17 and 0.2 cm, we made two crosses: F₂ (♀) × diploid red crucian carp (♂), and F₂ (♀) × F₁₀ tetraploid (♂). The ploidy levels of the progeny of the two crosses were examined by chromosome counting and DNA content measurement by flow cytometer. In the offspring of the former cross, tetraploids, trip-loids, and diploid were obtained. In the progeny of the latter cross, tetraploids and triploids were observed. The production of the different ploidy level fish in the progeny of the two crosses provided a further evidence that F₂ might generate triploid, diploid and haploid eggs. The presence of the male tetraploid found in F₂ (♀) × diploid red crucian carp (♂) suggested that the genotype of XXXY probably existed in the tetraploid progeny. The gonadal structures of the tetraploids and triploids indicated that both female and male tetraploids were fertile and the triploids were sterile. We concluded that the formations of different ploidy level eggs from F₂ were contributed by endoreduplication and fusion of germ cells.     

The effect of ploidy level on fitness in parthenogenetic flatworms

Although polyploidy plays an important role in speciation, its impact on fitness is still debated. One problem is that its adaptive significance can only be inferred by comparing forms with different ploidy that are identical in all other traits. This situation is uncommon, presumably because ploidy types often differ in reproduction mode, genetic background or habitat. Here we compare fitness in a system of triploid and tetraploid karyotypes of the planarian flatworm Schmidtea polychroa . Both types have the same type of sperm-dependent parthenogenesis and share the same genetic background and habitat. Hence, fitness differences, if any, can be attributed to different ploidy levels only. Contrary to the general assumption of a positive correlation between fitness and ploidy level, we showed that triploids produced 58% more offspring than tetraploids. Within each ploidy type, we identified groups of highly related clones using microsatellites. Significant variation among clonal groups in body size, offspring and cocoon number and hatching time indicated a genetic basis for variance in these traits. A small model shows that despite low fitness of tetraploids, stable coexistence of triploids and tetraploids can be explained by the recurrent origin of triploids from tetraploids and vice versa.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 191–198.     

Comparative studies on histological and ultra-structure of the pituitary of different ploidy level fishes

The histological and ultra-structure of the pituitary in diploid red crucian carp(Carassius auratus red var.),triploid crucian carp and allotetraploid hybrids within and after the breeding season were comparatively studied.The result showed that there were six endocrine cell types in the pituitary of these three kinds of fishes,and there was an obvious difference in cell size among different ploidy level fishes.As for the same type of pituitary cells,the cell size was increased gradually with the in- creasing ploidy level.In the breeding season,the allotetraploid hybrids had higher proportion of go- nadotropin cells(GTH)than triploids,and the triploids had higher proportion of GTH than diploids.The results were related to the earlier sexual maturity of allotetraploid hybrids and sterility of triploid cru- cian carp.On the other hand,among the three kinds of fishes,the proportion of somatotropin(STH) cells in triploids crucian carp was the highest,whereas that in allotetraploid hybrids was the lowest. The results might be connected with the faster growth rate of triploids and slower growth rate of al- lotetraploid hybrids.In addition,in GTH cells of meso-adenohypophysis after the breeding season, there were many endocrine particles in triploids,while those endocrine particles were released from the cells in allotetraploids and diploids.This result showed that the sterility of triploid crucian carp might be related to the hormone which was not released from the GTH cells.In a word,the present study indicated that the differences in the structure of pituitary among different ploidy level fishes contributed to their difference in the growth rate and gonadal development.     

Chromosome pairing and chiasma formation in autopolyploids of different Lathyrus species.

Chromosome pairing and chiasma formation were studied in natural and induced tetraploids (2n = 28) of Lathyrus odoratus (induced), Lathyrus pratensis (natural and induced), Lathyrus sativus (induced), and Lathyrus venosus (natural), as well as in triploids of L. pratensis and diploids of L. odoratus, L. pratensis, and L. sativus. All natural tetraploids appeared to be autotetraploids and their meiotic metaphase I behaviour was very similar to that of the induced autotetraploids, with average numbers of pairing partner switches exceeding 4 or even 5. Multivalent frequencies were high, but the numbers of chiasmata were not much higher than necessary to maintain the configurations. Interstitial chiasmata were common, but not predominant. Fertility was reduced, but sufficient for predominantly vegetatively reproducing species. The triploids of L. pratensis had an even higher multivalent frequency than the tetraploids, but still produced some viable progeny at or close to the tetraploid level, suggesting that in mixed populations of diploids and tetraploids, triploids can contribute to gene flow between the ploidy levels. There was no significant correlation between chiasma frequency and ring bivalent frequency in the diploids and multivalent frequency in the corresponding tetraploids. In the tetraploids, chiasma frequency and multivalent frequency were negatively correlated.     

Spatial ecological and genetic structure of a mixed population of sexual diploid and apomictic triploid dandelions

Ecological differentiation is widely seen as an important factor enabling the stable coexistence of closely related plants of different ploidy levels. We studied ecological and genetic differentiation between co-occurring sexual diploid and apomictic triploid Taraxacum section Ruderalia by analysing spatial patterns both in the distribution of cytotypes and in the distribution of genetic variation within and between the cytotypes. A significant relationship between ploidy level and elevation was found. This mode of ecological differentiation however, was not sufficient to explain the significant spatial structure in the distribution of diploids and triploids within the population. Strong congruence was found between the spatial genetic patterns within the diploids and within the triploids. We argue that this congruence is an indication of gene flow between neighbouring plants of different ploidy levels.     

Cytology and sexuality of 11 species of Elatostema (Urticaceae) in limestone karsts suggests that apomixis is a recurring phenomenon

Limestone karsts across southern China to southeastern Asia are renowned biodiversity hotspots. The karst are characterized by exposed calcareous rocks, seasonal droughts and thin soils that are deficient in N and P but with high Ca and Mg content. The stressful habitat may result in high biodiversity through mechanisms such as niche differentiation, hybridization, polyploidy and apomixis. The genus Elatostema (Urticaceae) has particularily high species diversity in this area and can be used a model genus to explore the mechanisms of speciation. We conducted cytological studies on 11 species of Elatostema from 12 populations in Guangxi, China. We found five populations to be diploid (2n = 26), and seven triploid populations (2n = 39). We infer x = 13 as the basic chromosome number of Elatostema. The chromosome numbers 2n = 26 and 2n = 39 were both found in populations of E. longistipulum, indicating that this species comprise both diploids and triploids. Both male and female plants of Elatostema were found to be diploid. In contrast, the triploids found were all female plants, and these produce seeds, presumably by apomixis. We found no clear relationship between ploidy level or reproductive pathway and endemism in Elatostema which might be because Elatostema species are wind‐pollinated and independent of biotic pollinators. However, a random sample of 11 karst species revealed that ca 2/3 appeared to be apomictic, suggesting that it is a widespread reproductive strategy of Elatostema in the limestone karsts of Guangxi. Apomixis enables plants to reproduce and disperse from a single individual, allowing ‘hopeful monsters’ adapted to a new habitat to form stable populations.     

Variation in flavonoid patterns in relation to chromosome changes in Gibasis schiedeana

The distribution of $\text{C-}\text{glycoflavones}$ has been examined in the leaves of plants from five diploid and 12 tetraploid populations of Gibasis schiedeana. Five different chromatographic patterns were found; one occurs only in a single population of diploid plants, two were found in seven populations of tetraploids and the other two in the remaining plants from both diploid and tetraploid populations. Flavonoids were also investigated in three different types of artificially produced triploids. The effects of the changes in ploidy, which are accompanied by Robertsonian fusion and variation in the number of B chromosomes as contributory factors in the observed differences in flavonoid patterns are discussed.     

Comparative studies on histological and ultra-structure of the pituitary of different ploidy level fishes

The histological and ultra-structure of the pituitary in diploid red crucian carp (Carassius auratus red var.), triploid crucian carp and allotetraploid hybrids within and after the breeding season were comparatively studied. The result showed that there were six endocrine cell types in the pituitary of these three kinds of fishes, and there was an obvious difference in cell size among different ploidy level fishes. As for the same type of pituitary cells, the cell size was increased gradually with the increasing ploidy level. In the breeding season, the allotetraploid hybrids had higher proportion of gonadotropin cells (GTH) than triploids, and the trploids had higher proportion of GTH than diploids. The results were related to the earlier sexual maturity of allotetraploid hybrids and sterility of triploid crucian carp. On the other hand, among the three kinds of fishes, the proportion of somatotropin (STH) cells in triploids crucian carp was the highest, whereas that in allotetraploid hybrids was the lowest. The results might be connected with the faster growth rate of triploids and slower growth rate of allotetraploid hybrids. In addition, in GTH cells of meso-adenohypophysis after the breeding season, there were many endocrine particles in triploids, while those endocrine particles were released from the cells in allotetraploids and diploids. This result showed that the sterility of triploid crucian carp might be related to the hormone which was not released from the GTH cells. In a word, the present study indicated that the differences in the structure of pituitary among different ploidy level fishes contributed to their difference in the growth rate and gonadal development.     

Habitat differentiation, hybridization and gene flow patterns in mixed populations of diploid and autotetraploid Dactylorhiza maculata s.l. (Orchidaceae)

Detailed ecological, morphological and molecular analyses were performed in mixed populations of diploid and autotetraploid Dactylorhiza maculata s.l. in Scandinavia. Comparisons were made with pure populations of either diploid ssp. fuchsii or tetraploid ssp. maculata. It was shown that mixed populations are the result of secondary contact between ssp. fuchsii and ssp. maculata. No patterns of recent and local autopolyploidization were found. Morphology and nuclear DNA markers (internal transcribed spacers of nuclear ribosomal DNA) showed that diploids and tetraploids from mixed populations have similar levels of differentiation to diploids and tetraploids from pure populations. Vegetation analyses, as well as analyses of environmental variables, revealed that diploid and tetraploid individuals in mixed populations are ecologically well differentiated on a microhabitat level. Diploids and tetraploids in pure populations have wider ecological amplitudes than they do in mixed populations. Triploid hybrids grew in intermediate microhabitats between diploids and tetraploids in the mixed populations. Plastid DNA markers indicated that both diploids and tetraploids may act as the maternal parent. Based on morphology and nuclear markers triploids are more similar to tetraploids than to diploids. There were indications of introgressive gene flow between ploidy levels. Plastid markers indicated that gene flow from diploid to tetraploid level is most common, but nuclear markers suggested that gene flow in opposite direction also may occur. Similar patterns of differentiation and gene flow appeared in localities that represented contrasting biogeographic regions. Disturbance and topography may explain why hybridization was slightly more common and the differentiation patterns somewhat less clear in the Scandinavian mountains than in the coastal lowland. An erratum to this article can be found at