Inter-population sex chromosome polymorphism in the grasshopper Podisma pedestris

The montane grasshopper Podisma pedestris exists in Europe in two chromosomally distinct kinds of population. One has an XO/XX sex chromosome mechanism and a diploid chromosome number of 23 male, 24 female. The other has a neo-XY/neo-XX system and a diploid number of 22 in each sex. The development of the neo sex system in this instance has resulted from an X/L₃ fusion which has converted the telocentric X element into a metacentric neo-X. In the neo-XY male this has led to a considerable restriction of chiasma formation in the region proximal to the centromere in the L₃ arm of the neo-X. Since this kind of chromosome change must initially have involved a single individual it could only have succeeded in a small population isolate which underwent rapid expansion immediately following the fusion. Such an origin would have been considerably facilitated by either a modification in sex ratio or else some form of meiotic drive.     

CHROMOSOMES IN TWENTY-FIVE SPECIES OF CHINESE MEM-BRACIDS (HOMOPTERA: MEMBRACIDAE)*

Abstract Chromosomes in 25 species of Membracidae are recorded. Numbers, size and behaviors of the chromosomes during meiosis and mitosis are used as specific or generic features for the taxonomy of this group. Chromosome numbers vary from n=5 to 12, and sex mechanism are of XO type except two species with neo-XY system. The histogram indicates that 2n=11 with XO sex mechanism is the modal chromosome number, and another type n=10 is also commonly found in this family.     

The karyotypes of two bark-lice species (Psocoptera, Psocomorpha, Amphipsocidae): the first description of the neo-XY sex chromosome system in Psocoptera

Karyotypes of two bark-lice species Amphipsocus japonicus End. and Dasypsocus japonicus End. (Amphipsocidae, Psocomorpha, Psocoptera) were studied for the first time. D. japonicus displayed 2n = 16 (14 + XX/X0). The XX/X0 sex chromosome system observed in this species is characteristic of the order Psocoptera. A. japonicus showed 2n = 16 (14 + neo-XY). This is the first observation of the neo-XY sex determination system in Psocoptera. In this species a large amount of constitutive heterochromatin was found in the original X-part of the neo-X chromosome.     

Aberrant chromosomal sex-determining mechanisms in mammals, with special reference to species with XY females

Both mouse and man have the common XX/XY sex chromosome mechanism. The X chromosome is of original size (5-6% of female haploid set) and the Y is one of the smallest chromosomes of the complement. But there are species, belonging to a variety of orders, with composite sex chromosomes and multiple sex chromosome systems: XX/XY1Y2 and X1X1X2X2/X1X2Y. The original X or the Y, respectively, have been translocated on to an autosome. The sex chromosomes of these species segregate regularly at meiosis; two kinds of sperm and one kind of egg are produced and the sex ratio is the normal 1:1. Individuals with deviating sex chromosome constitutions (XXY, XYY, XO or XXX) have been found in at least 16 mammalian species other than man. The phenotypic manifestations of these deviating constitutions are briefly discussed. In the dog, pig, goat and mouse exceptional XX males and in the horse XY females attract attention. Certain rodents have complicated mechanisms for sex determination: Ellobius lutescens and Tokudaia osimensis have XO males and females. Both sexes of Microtus oregoni are gonosomic mosaics (male OY/XY, female XX/XO). The wood lemming, Myopus schisticolor, the collared lemming, Dirostonyx torquatus, and perhaps also one or two species of the genus Akodon have XX and XY females and XY males. The XX, X*X and X*Y females of Myopus and Dicrostonyx are discussed in some detail. The wood lemming has proved to be a favourable natural model for studies in sex determination, because a large variety of sex chromosome aneuploids are born relatively frequently. The dosage model for sex determination is not supported by the wood lemming data. For male development, genes on both the X and the Y chromosomes are necessary.     

Molecular cytogenetic analysis reveals the existence of two independent neo-XY sex chromosome systems in Anatolian Pamphagidae grasshoppers

Background

Neo-XY sex chromosome determination is a rare event in short horned grasshoppers, but it appears with unusual frequency in the Pamphagidae family. The neo-Y chromosomes found in several species appear to have undergone heterochromatinization and degradation, but this subject needs to be analyzed in other Pamphagidae species. We perform here karyotyping and molecular cytogenetic analyses in 12 Pamphagidae species from the center of biodiversity of this group in the previously-unstudied Anatolian plateau.

Results

The basal karyotype for the Pamphagidae family, consisting of 18 acrocentric autosomes and an acrocentric X chromosome (2n♂?=?19, X0; 2n♀?=?20, XX), was found only in G. adaliae. The karyotype of all other studied species consisted of 16 acrocentric autosomes and a neo-XY sex chromosome system (2n♂♀?=?18, neo-XX♀/neo-XY♂). Two different types of neo-Y chromosomes were found. One of them was typical for three species of the Glyphotmethis genus, and showed a neo-Y chromosome being similar in size to the XR arm of the neo-X, with the addition of two small subproximal interstitial C-blocks. The second type of the neo-Y chromosome was smaller and more heterochromatinized than the XR arm, and was typical for all Nocarodeini species studied. The chromosome distribution of C-positive regions and clusters of ribosomal DNA (rDNA) and telomeric repeats yielded additional information on evolution of these neo-XY systems.

Conclusion

Most Pamphagidae species in the Anatolian region were found to have neo-XY sex chromosome systems, belonging to two different evolutionary lineages, marked by independent X-autosome fusion events occurred within the Trinchinae and Pamphaginae subfamilies. The high density of species carrying neo-XY systems in the Anatolian region, and the different evolutionary stage for the two lineages found, one being older than the other, indicates that this region has a long history of neo-XY sex chromosome formation.

     

A complex sex-chromosome system in the hare-wallaby Lagorchestes conspicillatus Gould

Among specimens of the spectacled hare-wallaby Lagorchestes conspicillatus Gould (Marsupialia, family Macropodidae) 4 males had 15 chromosomes and 2 females 16 chromosomes. The sex chromosomes are X₁X₁X₂X₂ in the female and X₁X₂Y in the male, the Y being metacentric and both X chromosomes are acrocentric. In about 96% of sperm mother cells at meiosis the sex chromosomes form a chain trivalent and in more than 99% of these this orients convergently so that the X₁ and X₂ move to the same pole. Evidence is presented that L. conspicillatus has evolved from a form with 22 chromosomes including a small X and a minute Y. Autoradiographic studies show that the proximal fifth of the X₁ chromosome replicates late. This is probably the ancestral X chromosome which has been translocated to an autosome. The fate of the original Y is obscure but an hypothesis is proposed that it forms the centromeric region of the Y. A single male had 14 chromosomes and was heterozygous for a translocation involving the centric fusion of two acrocentric autosomes. In about 30% of sperm mother cells the autosomal trivalent did not disjoin regularly but, despite this, all secondary spermatocytes observed at metaphase 2 had balanced complements of chromosomes. It is assumed that unbalanced secondary spermatocytes died before reaching metaphase.     

二十五种中国角蝉的染色体(英文)

本文记载了中国25种角蝉的染色体,研究表明染色体的数目、大小及其在减数分裂过程中的行为具有种或属一级的分类特征。该科昆虫染色体的数目变异在n＝5到12之间,众数为n＝11,另外,n＝10的类型也较为普遍。绝大多数种类的性别决定机制为XO型,仅个别种类具有新XY性染色体系统。     

Chromosome polymorphism and C-banding variation of the brachypterous grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae) in Hokkaido, northern Japan

The grasshopper Podisma sapporensis consists of two main chromosome races in Hokkaido. The western group of populations of P. sapporensis, belonging to the XO race, has a diploid number of chromosomes 2n = 23 in the male and 2n = 24 in the female (sex determination XO male/XX female). The eastern group of populations of this species, belonging to the XY race, differs from the western one as a result of Robertsonian translocation between the originally acrocentric X chromosome and M5 autosome in homozygous state, having resulted in the forming of chromosome sex determination neo-XY male/neo-XX female (2n = 22). These races are geographically isolated by the mountainous system consisting of the Mts Daisetsu and Hidaka range, occupying the central part of the island. The hybrid zones between the races have not so far been discovered. Various levels of polymorphism for the pericentric inversions and C-banding variation exist in different chromosomes throughout populations in both chromosome races. In some solitary populations (the population at the summit of Mt Yotei, populations in the vicinity of Naganuma, Oketo, and Tanno) pericentric inversions are fixed in some pairs of chromosomes, which enables marking of the discrete karyomorphes. In the Mt Daisengen population all chromosomes are two-armed as a result of fixing the pericentric inversions. These facts contradict karyotypical conservatism of the tribe Podismini. The level of diversity of P. sapporensis karyotypes could provide a new perspective on the evolutionary process of different karyotype in Orthoptera. The considerable occurrence of polymorphism in chromosomes suggests that karyotypic diversification is undergoing in P. sapporensis. The authors also proposed that P. sapporensis would be divided into four chromosome subraces in the XO chromosome race and two chromosome subraces in the XY race, on the basis of karyotypic features. These races may have been established by fundamental climatic changes during the glacial epoch.     

Reversion of XO to XY sex chromosome mechanism in a phasmid

Summary The sex chromosomes of the male phasmid Isagoras schraderi Rehn comprise an X and a Y, — each with a submedian kinetochore, and one euchromatic and one heterochromatic arm. At meiosis X and Y form an unequal sex bivalent in which the euchromatic arms are terminally associated. Relatively recent reversion from the XO-XX mechanism characteristic of the Phasmidae is indicated by the presence of the euchromatic arm in both X and Y. The diploid number of the male is 34.Unequal autosomal bivalents are found at meiosis in two other species of Isagoras — Isagoras subaquiles Rehn and Isagoras sp. — and in Pseudophasma menius Westwood. The chromosome complements of these species are described.     

Sex chromosome-autosome translocations in the leaf-nosed bats, family Phyllostomidae. II. Meiotic analyses of the subfamilies Stenodermatinae and Phyllostominae

Analyses of meiotic pairing and synaptonemal complexes of the composite sex chromosomes of male phyllostomid bats with X-autosome or X- and Y-autosome translocations were performed using Giemsa and silver staining procedures. Typical mammalian sex vesicles were absent in all species analyzed. Stenodermatine species with X-autosome translocations possessed an open ring and tail configuration of the XY1Y2 trivalent. Species with both X- and Y-autosome translocations possessed a closed ring and tail configuration of the neo-XY bivalent. In both cases, the tail represented the autosomal short arm of the X paired with its homologue, either the Y2 in XY1Y2 species or the autosomal arm of the composite Y in neo-XY species. Autosomal pairing of the composite sex bivalent in neo-XY species replaced an association between the original X and Y in late prophase I. The absence of a sex vesicle, the unusual pairing configurations of the composite sex chromosomes, and the presumed absence of meiotic nondisjunction in these species is discussed in light of current hypotheses of sex chromosome behavior in male gametogenesis in mammals.     

Chromosome variation in British populations of Oncopsis (Hemiptera:Cicadellidae)

The British species of Oncopsis fall into two groups with respect to male karyotype. Four species—O. avallanae, O. carpini and O. subangulata, together with an undescribed new species close to carpini—consistently show ten autosome pairs and a single X-chromosome (2n=10AII+XO). In O. tristis too the XO state predominates but single neo-sex chromosome variants with nine and eight autosome pairs respectively have also been found. The two remaining species-O. alni and O. flavicollis—both regularly include derived neo-XY states involving the incorporation of autosomal material onto the X(2n=9AII+XY). The single population of O. alni studied was entirely neo-XY but the situation in O. flavicollis proved more complex. Montane populations which occur on Betula pubescens are XO-monomorphic whereas populations in lowland woodlands are polymorphic, including both XO and neo-XY types. In such situations the XO forms are found predominantly on B. pubescens whereas the XY morphs predominate on a second species of birch, B. pendula, which is absent from montane woodlands. In all three species where the neo-XY state is present, different autosomes have been involved in the fusion process.     

Genetic and chromosomal polymorphism in hybridizing populations of the grasshopper Podisma pedestris

The grasshopper Podisma pedistris occurs in two chromosome races, which have XO/XX and neo-XY sex chromosome systems. We have studied chromosomal and electrophoretic variation in populations where these two races meet and hybridize, in an area near the town of Seyne, Alpes Maritimes, southern France. Allozyme variation, at 21 loci in 11 populations, does not seem to show any relationship to the underlying cline in the frequency of the two chromosome types. This indicates that the chromosomal cline does not offer a strong barrier to the flow of genes at other loci. The XO/XX race in this area occurs on a single plateau, isolated from other populations with the same karyotype. It is suggested that this form is only able to persist here because the introgression of neo-XY chromosomes is inhibited by steep cliffs, which tend to keep the two races apart.     

Nature and distribution of heterochromatinized regions in the chromosomal races of Pycnogaster cucullata (Insecta,Orthoptera)

Populations belonging to the XO and neo-XY races of P. cucullata have been analysed with C-banding and fluorescent DNA-binding dyes. The extent of C-heterochromatin variation was found to be considerably greater than that described in previous papers. Most of the heterochromatinized regions are GC-rich and could be derived from the GC-rich sequences of the NORs. Since the gain of heterochromatin does not involve detectable modification of the chromosome size, the heterochromatinization process may be considered as an example of euchromatin transformation. On the other hand, the distribution of heterochromatin in the sex chromosomes seems to be markedly non-random, probably due to the selective advantage of a complementary distribution between neo-X and neo-Y chromosomes.     

Cytomolecular analysis of the male sex chromosome of Tropidacris cristata grandis (Thunberg, 1824) (Orthoptera: Romaleidae)

Many species of grasshopper have an XX/XO sex chromosome system, including Tropidacris cristata grandis (23, XX/XO). The X chromosome behaves differently from the autosomes, but little is known about its origin and molecular composition. To better understand the genomic composition and evolutionary processes involved in the origin of the sex chromosomes, we undertook an analysis of its meiotic behavior, heterochromatin distribution and microdissection in T. c. grandis. Analysis of meiotic cells revealed a difference in the behavior of the X chromosome compared to the autosomes, with different patterns of condensation and cellular arrangement. Heterochromatic terminal blocks were predominant. The chromosome painting revealed a bright block in the centromeric/pericentromeric region of the X chromosome and slight markings in the other regions. In the autosomes, the X chromosome probe hybridized in the centromeric/pericentromeric region, and hybridization signals on terminal regions corresponding to the heterochromatic regions were also observed. The results showed that the X chromosome contains a significant amount of repetitive DNA. Based on the hybridization pattern, it is possible that the autosomes and sex chromosomes of T. c. grandis have a similar composition of repetitive DNAs, which could mean that the X chromosome has an autosomal origin.     

A high frequency of XO offspring from X(Paf)Y* male mice: evidence that the Paf mutation involves an inversion spanning the X PAR boundary

It has previously been reported that 19% of the daughters of males carrying the X-linked mutation patchy fur (Paf) are XO with a maternally derived X chromosome. We now report that hemizygous Paf males that also carry the variant Y chromosome Y*, show a much increased XO production ( approximately 40% of daughters). We hypothesize that the Paf mutation is associated with an inversion spanning the pseudoautosomal region (PAR) boundary, and that this leads to preferential crossing over between the resulting inverted region of PAR and an equivalent inverted PAR region within the compound Y* PAR. This would lead to the production of dicentric X and acentric Y products and consequent sex chromosome loss. This interpretation is supported by analysis of the sex chromosome complements at the second meiotic metaphase, which revealed a high incidence of dicentrics. Another curious feature of the Paf mutation is that mice that are homozygous Paf have more hair than mice that are hemizygous Paf. This can be explained if the Paf mutation is a hypomorphic mutation that escapes X inactivation because, unlike the wild type allele, it is now located within the PAR.     

Inter-population sex chromosome polymorphism in the grasshopper Podisma pedestris

Populations of the alpine grasshopper Podisma pedestris are either completely XO/XX or else completely neo-XY/neo-XX in character. The neo-XY form is limited in its occurrence to near the extreme southwest edge of the present distribution of the species. Both kinds of population also contain B-chromosomes. These are of two types differing with regard to size, stability and origin. Both types can occur in the same population but have not so far been found in the same individual. The pattern of distribution of the larger, mitotically-stable supernumerary suggests that it might be a remnant X-chromosome which became converted into a B in the initial phase of neo-XY evolution. The smaller, partly unstable supernumerary, on the other hand, may well have originated from a heteromorphic S₁₁ pair also found in some of the populations with small B's. The available evidence points to the neo-XY system having evolved following a secondary movement of the species into the higher ground it now occupies after the climatic amelioration at the end of the last ice age.     

Meiosis and the Neo- XY system of Dichroplus vittatus (Melanoplinae, Acrididae): a comparison between sexes

The origin of neo-XY sex systems in Acrididae is usually explained through an X-autosome centric fusion, and the behaviour of the neo-sex chromosomes has been solely studied in males. In this paper we analysed male and female Dichroplus vittatus. The karyotype comprises 2n = 20 chromosomes including 9 pairs of autosomes and a sex chromosome pair that includes a large metacentric neo-X and a small telocentric neo-Y. We compared the meiotic behaviour of the sex bivalent between both sexes. Mean cell autosomal chiasma frequency was low in both sexes and slightly but significantly higher in males than in females. Chiasma frequency of females increased significantly when the sex-bivalent was included. Chiasma distribution was basically distal in both sexes. Behaviour of the neo-XY pair is complex as a priori suggested by its structure, which was analysed in mitosis and meiosis of diploid and polyploid cells. During meiosis, orientation of the neo-XY is highly irregular; only 21% of the metaphase I spermatocytes show standard orientation. In the rest of cells, the alternate or simultaneous activity of an extra kinetochore in the distal end of the short arm (XL) of the neo-X, determined unusual MI orientations and a high frequency of non-disjunction and lagging of the sex-chromosomes. In females, the neo-XX bivalent had a more regular behaviour but showed 17% asynapsis in the XL arm which, in those cases orientated its distal ends towards opposite spindle poles suggesting, again, the activity of a second kinetochore. The dicentric nature and the unstable meiotic behaviour of the sex neo-chromosomes of D. vittatus suggest a recent origin of the sex determination mechanism, with presumable adaptive advantages which could compensate their potential negative heterosis. Our observations suggest that the origin of the neo-sex system was a tandem fusion of two original telocentric X-chromosomes followed by another tandem fusion with the small megameric bivalent and a further pericentric inversion of the neo-X. The remaining autosomal homolog resulted in the neo-Y chromosome. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical and structural variations of the X chromosomes and no. 2 autosomes in mandarin vole, Microtus mandarinus (Rodentia)

Here we describe our studies on Microtus mandarinus faeceus of Jiangyan in Jiangsu province of China. By karyotype and G-banding analysis we have found variation in chromosome number and polymorphisms of the X chromosome and the second pair of autosomes of the subspecies. Chromosome number of the subspecies is 2n=47-50. The subspecies has three kinds of chromosomal sex: XX, XO and XY, among which one of the X chromosomes is subtelocentric (X(ST)) and the other is metacentric (X(M)). After comparing karyotypes of different subspecies, we found the specific cytogenetic characteristics of Microtus mandarinus, that is they have three kinds of chromosomal sex: XX, XO and XY; X chromosomes are heteromorphic; the chromosome number of female individuals are one less than male individuals; chromosome number of XX individuals are equal to that of XO ones. We hypothesize that Robertsonian translocation is the main reason of the polymorphism of the second pair of autosomes and variety of chromosome number, and it also causes the chromosome number evolution in different subspecies of Microtus mandarinus.     

The process of a Y-loss event in an XO/XO mammal, the Ryukyu spiny rat

The Ryukyu spiny rat, Tokudaia osimensis, has an XO/XO sex chromosome constitution, lacking a Y chromosome and the mammalian sex-determining gene SRY. To investigate the Y-loss event, we traced three proto-Y-linked genes, RBMY1A1, EIF2S3Y, and KDM5D, in the genome. The original Y-linked RBMY1A1 was lost as well as SRY, and the remaining RBMY1A1 was a processed pseudogene on autosome. In contrast, EIF2S3Y and KDM5D were conserved in genomes of both sexes as a result of their translocation from the Y chromosome to the X chromosome and/or autosomes. Furthermore, these genes were expressed in gonads and brains of both sexes. Our study indicated a loss of Y-linked genes with important male functions to be necessary for the Y chromosome to disappear. These functions might have been retained through the acquisition of new genes, and therefore, the Y-loss has had no harmful effect on the maintenance of this species.     

The number of x chromosomes causes sex differences in adiposity in mice

Sexual dimorphism in body weight, fat distribution, and metabolic disease has been attributed largely to differential effects of male and female gonadal hormones. Here, we report that the number of X chromosomes within cells also contributes to these sex differences. We employed a unique mouse model, known as the "four core genotypes," to distinguish between effects of gonadal sex (testes or ovaries) and sex chromosomes (XX or XY). With this model, we produced gonadal male and female mice carrying XX or XY sex chromosome complements. Mice were gonadectomized to remove the acute effects of gonadal hormones and to uncover effects of sex chromosome complement on obesity. Mice with XX sex chromosomes (relative to XY), regardless of their type of gonad, had up to 2-fold increased adiposity and greater food intake during daylight hours, when mice are normally inactive. Mice with two X chromosomes also had accelerated weight gain on a high fat diet and developed fatty liver and elevated lipid and insulin levels. Further genetic studies with mice carrying XO and XXY chromosome complements revealed that the differences between XX and XY mice are attributable to dosage of the X chromosome, rather than effects of the Y chromosome. A subset of genes that escape X chromosome inactivation exhibited higher expression levels in adipose tissue and liver of XX compared to XY mice, and may contribute to the sex differences in obesity. Overall, our study is the first to identify sex chromosome complement, a factor distinguishing all male and female cells, as a cause of sex differences in obesity and metabolism.