Experimental hybridisation between X0 and XY chromosome races in the grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae). I. Cytological analysis of embryos and F1 hybrids

The results of experimental hybridisation between some chromosome subraces belonging to the X0 and XY chromosome races of the brachypterous grasshopper P. sapporensis are presented. Pre-zygotic reproductive isolation mechanisms in experimental pairs were not confirmed. In crossings of XY-standard x X0-standard and XY-standard x X0-Naganuma chromosome subraces, a zygotic barrier has been found. All embryos of XY-standard x X0-standard crosses and the vast majority of embryos of XY-standard x X0-Naganuma crosses were obtained from female diploid or haploid/diploid cells as a result of parthenogenesis. In very rare cases, when the zygotic barriers had been surmounted, normal embryo heterozygotes and a F1 hybrid generation were obtained in XY-standard x X0-Naganuma crosses. On the contrary, crosses between the XY-Tanno and X0-standard subraces gave viable offspring in spite of many chromosome differences such as a X-A translocation and fixed pericentric inversions in four pairs of autosomes. The results obtained do not support the hypothesis that chromosomal differences play a key role in restricting gene flow between X0 and XY races of P. sapporensis. The presence of crossing barriers explains the phenomena of the purity of the X0 and XY chromosomes races.     

Population cytogenetics of the genus Caledia (Orthoptera: Acridinae)

The genus Caledia contains two species. C. species nova 1 is restricted to the Oriomo Plateau of S.W. Papua and has a complement of twelve telocentric chromosomes. The second species C. captiva has a much wider distribution pattern—from S.W. Papua in the North, down the entire Eastern seaboard of Australia to Southern Victoria. It is also found in the Northern Territory. Although the chromosome number is the same as C. species nova 1, four major and distinct chromosomal races can be distinguished in C. captiva. — The basic ancestral race is found in Tropical North Queensland at the base of the Cape York Peninsula. All twelve chromosomes are telocentric and the karyotypic organization is similar to that found in C. species nova 1 and in other Acridines. A second, general purpose karyotypic race has a wide distribution between S.W. Papua, Arnhem Land and the East Australian coast as far South as Brisbane. It is considered a derivative form of the ancestral type and is fixed for small pericentric inversions on seven pairs of chromosomes. In the South-Eastern Queensland region there exists a further race which carries large pericentric inversions on all the autosomes and the X chromosome. The situation here is confounded since the basic chromosomes can be represented as either acro or telocentrics. Various levels of polymorphism for the inversions exist between different chromosomes in different populations indicating considerable differentiation within this zone. This race is almost completely surrounded by the general purpose karyotype where the races are contiguous in certain parts of the range. — The South-Eastern corner of Australia is characterised by a chromosome race quite different from those found further North. Here a complex pericentric inversion system exists involving a series of seven small inversions and larger inversions on chromosomes 1, 2, 4 and 10. Chromosomes 2 and 4, in particular, are highly polymorphic. — The presence and persistence of these 4 chromosomal races can be accounted for in terms of the known climatic changes which have occurred in this region in the recent past.     

B chromosomes, translocation between B and autosomes, and C-heterochromatin polymorphism of the grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae) in Hokkaido, northern Japan.

Seven categories of B chromosomes found in the brachypterus grasshopper Podisma sapporensis from Hokkaido populations differ in structure, size, and C-band content. The interchange between B and one autosome from M3 and sporadically M7 was observed in most of the populations examined. Such an interaction between standard and non-standard chromosomal set provides an insight into the integration of supernumerary chromosome. In addition, C-heterochromatin polymorphism was also identified in male karyotypes in some populations. These facts indicate P. sapporensis is a highly polymorphic species from the cytogenetic point of view.     

First evidence of Wolbachia infection in populations of grasshopper Podisma sapporensis (Orthoptera: Acrididae)

The brachypterous grasshopper Podisma sapporensis (Orthoptera: Acrididae) is distributed throughout the Sakhalin, Kunashir and Hokkaido Islands. Karyotypes of this species consist of two major chromosomal races with different sex chromosome systems, XO/XX and XY/XX. Molecular phylogeographic analysis of the chromosome races and subraces confirms the genetic divergence of the races and subraces in P. sapporensis. Here we first report that P. sapporensis is infected with Wolbachia consisting of three variants on wsp locus, while gatB locus was monomorphic. Furthermore, observation of cell tissue of P. sapporensis using electron microscopy confirmed the infection of Wolbachia that was inferred from polymerase chain reaction and revealed the distribution of the bacteria in the head, thorax and abdomen of P. sapporensis embryos. Our finding may shed new light on Wolbachia as a possible agent causing hybrid dysfunction resulting from experimental crosses between chromosome races or subraces of P. sapporensis.     

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.     

Cytogenetics, cytotaxonomy and chromosomal evolution of Chrysomelinae revisited (Coleoptera, Chrysomelidae)

Nearly 260 taxa and chromosomal races of subfamily Chrysomelinae have been chromosomally analyzed showing a wide range of diploid numbers from 2n = 12 to 2n = 50, and four types of male sex-chromosome systems. with the parachute-like ones Xy(p) and XY(p) clearly prevailing (79.0%), but with the XO well represented too (19.75%). The modal haploid number for chrysomelines is n = 12 (34.2%) although it is not probably the presumed most plesiomorph for the whole subfamily, because in tribe Timarchini the modal number is n = 10 (53.6%) and in subtribe Chrysomelina n = 17 (65.7%). Some well sampled genera, such as Timarcha, Chrysolina and Cyrtonus, are variable in diploid numbers, whereas others, like Chrysomela, Paropsisterna, Oreina and Leptinotarsa, are conservative and these differences are discussed. The main shifts in the chromosomal evolution of Chrysomelinae seems to be centric fissions and pericentric inversions but other changes as centric fusions are also clearly demonstrated. The biarmed chromosome shape is the prevalent condition, as found in most Coleoptera, although a fair number of species hold a few uniarmed chromosomes at least. A significant negative correlation between the haploid numbers and the asymmetry in size of karyotypes (r = -0.74) has been found from a large sample of 63 checked species of ten different genera. Therefore, the increases in haploid number are generally associated with a higher karyotype symmetry.     

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.     

Sex chromosome differences among the three races (alpha, beta, gamma) of the snail intermediate host of Schistosoma mekongi, Neotricula aperta

Chromosome analyses were performed on three races (alpha, beta, gamma) of Neotricula aperta which were previously reported to show variation in the chromosome number and pairing in meiosis. We used an air-drying method, which was more reliable for chromosome preparations from fresh animal tissues than a squash method. Each of the races had the same number of chromosomes, 2n=33 for males, and 2n=34 for females. The sex determination system was XO type (male: 32+X, female: 32+XX). The sex chromosome of each race was distinct in its morphology, but not in its length. Karyotyping revealed that the X-chromosome of the alpha race was metacentric (M), whereas it was acrocentric (A) in the beta and the gamma races. An association between the X-chromosome and a small autosome in meiosis suggested that a neo-Y chromosome probably lies in the terminal region of the small autosome.     

Lack of mitochondrial DNA divergence between chromosome races of the common shrew, Sorex araneus, in Sweden. Implications for interpreting chromosomal evolution and colonization history

The common shrew, Sorex araneus, has one of the most variable karyotypes among mammals, displaying numerous chromosome races throughout its distribution. The six chromosome races present in Sweden can be categorized in two different karyotypic groups, the west and north European karyotypic groups (western and northern). Three races belonging to the western group are considered to have arisen through whole arm reciprocal translocations (WARTs). Race formation through this process requires a bottleneck event. In the present study we sequenced a part of the mitochondrial DNA (mtDNA) genome to investigate molecular differences between the chromosome races in Sweden. We found no mtDNA differentiation between the mainland chromosome races or the karyotypic groups. Genetic variation is as large between populations within a race as between populations among the races or karyotypic groups, suggesting that the karyotypic groups might have originated in a common glacial refugium. The noticeable exception is the Oland race, which shows higher mtDNA diversity compared to the other Swedish races, indicating a divergent origin difficult to explain. Mitochondrial DNA variation in Sweden suggests that most haplotypes arose in situ and that the populations has undergone a rapid size expansion. Altogether, the mtDNA data are in agreement with the WART hypothesis, which still holds as the most plausible variant of karyotype evolution for three of the chromosome races of the common shrew in Sweden.     

横断山区四种湍蛙的细胞遗传学研究

通过染色体组型分析,C带(BSG技术)分析及一种简便的Ag-NORs带分析,对四川湍蛙、理县湍蛙、棕点湍蛙和棘皮湍蛙的种间关系、染色体的演化及其性染色体等问题进行了初步探讨。结果表明:(1)四川湍蛙、理县湍蛙和棕点湍蛙之间的亲缘关系较近,而它们与棘皮湍蛙的亲缘关系较远;(2)在近缘种的分化中,染色体结构异染色质的变化和臂间倒位是重要的因素之一,这在小型染色体上表现得尤为突出;(三)四川湍蛙具有在形态上分化很明显的性染色体。C带分析表明,此性染色体主要由常染色质构成,但在其Y染色体的长臂上存在明显的中间C带,推测尚处于性染色体分化的初期阶段。     

Analysis of chromatin-associated fiber arrays

The distribution of constitutive heterochromatin has been investigated in four chromosomal races of the grasshopper Caledia captiva (2n= 23 /24 ) by the C-banding technique. Each of the four races was found to have a distinctive banding pattern which is associated with the inter-racial differences in chromosomal rearrangements. — The Ancestral race has a telocentric chromosome complement with large procentric C-bands which are structurally double on six pairs of chromosomes. The centromeres are unstained. — The General Purpose race has a C-banding pattern very similar to that seen in other Acridine grasshoppers with the majority of its chromosomes showing a centromeric localisation of the bands. — The two southern races, which show a complex polymorphism for presumed pericentric inversions on all twelve chromosomes, also show an unusually high level of interstitial and terminal C-bands. The different locations and numbers of these bands allow unambiguous identification of all the chromosome pairs within the complement. — In two cases, there is good evidence to indicate that a C-band redistribution between acrocentric and metacentric chromosomes has occurred by pericentric inversion. Furthermore, C-band variation on the long arm of the metacentric X-chromosome indicates the presence of a large paracentric inversion. This double inversion system has involved over 95% of the X-chromosome. — The interstitial and terminal C-bands probably have not resulted from heterochromatin movement within the complement but, more likely, have arisen by saltatory duplication of pre-existing sequences on the chromosome. — A new nomenclature system for banded chromosomes is proposed which allows most kinds of chromosomal restructuring and rearrangement to be adequately enumerated.     

Karyotypic evolution and phylogeny of Mexican Passalidae (Coleoptera: Polyphaga: Scarabaeoidea)

The chromosomes of 26 taxa from Mexico of the tribes Passalini (three species) and Proculini (23 species) have been studied, increasing the karyotypically known species of the family Passalidae to 56. Karyotypic dynamism is high since the diploid number varies from 18 to 44 in the tribe Proculini. and from 25 to 31 in the tribe Passalini. In addition, supernumerary chromosomes, chromosome heteromorphism, translocations and possible sex multivalents have been found. These results contrast with the numerical conservatism found in related families of the superfamily Scarabaeoidea. However, both tribes are conservative with regard to sex determination, as all species of Proculini have male XY chromosomes whereas species of the Passalini have male XO chromosomes. It is postulated that differences in patterns shown by these two tribes are mainly due to population structure, because many species of Proculini are endemic to restricted areas of Meso and South America, favouring the settlement of karyotypic changes, whereas species of Passalini are distributed over large areas in the lowlands. It is also postulated that the ancestral karyotypic formula of the family is close to 12–14 pairs of autosomes although the ancestral male sex determination may be either XY or XO. At present only a weak relationship between morphological and karyotypic evolution has been found, which together with the marked numerical variability found within and between genera make it difficult to obtain phylogenetic conclusions from karyotypic results.     

B chromosomes of the Podisma sapporensis Shir. (Orthoptera, Acrididae) analysed by chromosome microdissection and FISH

The analysis of the distribution of repetitive DNA of the B chromosomes of Podisma sapporensis in the A and B chromosomes of the natural populations and in A chromosomes of three other species of the Podismini grasshoppers were made. DNA-libraries of the B chromosome and the euchromatic segment of the A chromosome of P. sapporensis were generated by meiotic chromosome microdissection followed by degenerated oligonucleotide primed polymerase chain reaction (DOP-PCR). Paints based on these DNA-libraries were used for FISH analysis to detect localization of homologous sequences in A and B chromosomes of P. sapporensis from different natural populations. On the basis of the FISH analysis the authors suggest that evolution of the B chromosomes in Podisma sapporensis was associated mainly with the insertions of "alien DNA sequences" into ancestral A chromosome and their further amplification. The number of initial sites of amplifications differed in the different Bs, the distance between these sites also varying. Karyotype evolution in P. sapporensis was associated partly with the insertion of "alien DNA sequences" into pericentromeric chromosomal regions. Insertion into the small short arms of the acrocentric chromosomes followed, with the DNA amplification leading to the formation of the additional C-heterochromatic arms or euchromatic-like regions of different size.     

New karyotypes and somatic and germ-cell banding in Akodon arviculoides (Rodentia, Cricetidae).

Chromosomal polymorphism resulting from three autosomal pericentric inversions and a complex rearrangement involving the largest chromosome of the complement (pair 1) in Akodon arviculoides (2n= 14, 15) is reported. G- and C-banding patterns in somatic and meiotic cells allowed the precise identification of all chromosomes and rearrangements. In meiosis of male specimens with 2n = 15, a large trivalent reflecting the complex rearrangement in autosomal pair 1 was observed. Two possible explanations for it are discussed. G- and C-bands in diplotene cells in heterozygotes for the inversions showed different configurations depending on the pairing in the inverted segments. Chiasma frequency data fro three specimens are analyzed.     

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.     

Karyotype differentiation between two stickleback species (Gasterosteidae)

The stickleback family (Gasterosteidae) of fish is less than 40 million years old, yet stickleback species have diverged in both diploid chromosome number (2n) and morphology. We used comparative fluorescence in situ hybridization (FISH) on 2 stickleback species, Gasterosteus aculeatus (2n = 42) and Apeltes quadracus (2n = 46), to ascertain the types of chromosome rearrangements that differentiate these species. The A. quadracus karyotype contains more acrocentric and telocentric chromosomes than the G. aculeatus karyotype. By using bacterial artificial chromosome probes from G. aculeatus in our FISH screen, we found that 6 pericentric inversions and 2 chromosome fusions/fissions are responsible for the greater number of acrocentric and telocentric chromosomes in A. quadracus. While most populations of G. aculeatus have an XX/XY sex chromosome system, A. quadracus has a ZZ/ZW sex chromosome system, as previously reported. However, we discovered that a population of A. quadracus from Connecticut lacks heteromorphic sex chromosomes, providing evidence for unexpected sex chromosome diversity in this species.     

Comparative FISH analysis of distribution of B chromosome repetitive DNA in A an d B chromosomes in two subspecies of Podisma sapporensis (Orthoptera, Acrididae)

FISH analysis of B chromosome repetitive DNA distribution in A and B chromosomes of two subspecies of Podisma sapporensis (P. s. sapporensis and P. s. krylonensis) was performed. In the B chromosomes, C-positive regions contained homologous DNA repeats present also in some C-positive A chromosome regions. Most C-negative regions contained DNA repeats characteristic of A chromosome euchromatic regions. The two subspecies analyzed differed in the location of A chromosome regions enriched with repeats homologous to repeats of B chromosomes. The only common region enriched with these B chromosome repeats in both subspecies was the X chromosome pericentromeric region. The origin of B chromosomes in P. sapporensis is discussed.     

Cytogenetical studies in five Atlantic Anguilliformes fishes

The order Anguilliformes comprises 15 families, 141 genera and 791 fish species. Eight families had at least one karyotyped species, with a prevalence of 2n = 38 chromosomes and high fundamental numbers (FN). The only exception to this pattern is the family Muraenidae, in which the eight species analyzed presented 2n = 42 chromosomes. Despite of the large number of Anguilliformes species, karyotypic reports are available for only a few representatives. In the present work, a species of Ophichthidae, Myrichthys ocellatus (2n = 38; 8m+14sm+10st+6a; FN = 70) and four species of Muraenidae, Enchelycore nigricans (2n = 42; 6m+8sm+12st+16a; FN = 68), Gymnothorax miliaris (2n = 42; 14m+18sm+10st; FN = 84), G. vicinus (2n = 42; 8m+6sm+28a; FN = 56) and Muraena pavonina (2n = 42; 6m+4sm+32a; FN = 52), collected along the Northeastern coast of Brazil and around the St Peter and St Paul Archipelago were analyzed. Typical large metacentric chromosomes were observed in all species. Conspicuous polymorphic heterochromatic regions were observed at the centromeres of most chromosomes and at single ribosomal sites. The data obtained for Ophichthidae corroborate the hypothesis of a karyotypic diversification mainly due to pericentric inversions and Robertsonian rearrangements, while the identification of constant chromosome numbers in Muraenidae (2n = 42) suggests a karyotype diversification through pericentric inversions and heterochromatin processes.     

Sex, not genotype, determines recombination levels in mice

Recombination, the precise physical breakage and rejoining of DNA between homologous chromosomes, plays a central role in mediating the orderly segregation of meiotic chromosomes in most eukaryotes. Despite its importance, the factors that control the number and placement of recombination events within a cell remain poorly defined. The rate of recombination exhibits remarkable species specificity, and, within a species, recombination is affected by the physical size of the chromosome, chromosomal location, proximity to other recombination events (i.e., chiasma interference), and, intriguingly, the sex of the transmitting parent. To distinguish between simple genetic and nongenetic explanations of sex-specific recombination differences in mammals, we compared recombination in meiocytes from XY sex-reversed and XO females with that in meiocytes from XX female and XY male mice. The rate and pattern of recombination in XY and XO oocytes were virtually identical to those in normal XX females, indicating that sex, not genotype, is the primary determinant of meiotic recombination patterns in mammals.     

Oogenesis and the Chromosomes of the Parthenogenic Root-knot Nematode Meloidogyne incognita

220 populations of Meloidogyne incognita and related forms from 46 countries reproduced by mitotic parthenogenesis (apomixis). Determination of somatic chromosome numbers from oogonia and oocytes revealed the existence of a predominant, possibly triploid race A with 3n = 40 to 46 and a rare, diploid race B with 2n = 32 to 36 chromosomes. There is no correlation between cytological races and the four recognized host races of this species. The characteristic behavior of prophase I chromosomes of maturing oocytes, which results in a prolonged prophase stage, is a unifying feature of all forms of M. incognita and supports monophyletic evolution, distinct from that of other Meloidogyne species. Extensive chromosomal polymorphism detected among populations can be helpful in elucidating the cytological pathway of evolution of the species.