Parallel polymorphism for supernumerary segments inChorthippus parallelus (zetterstedt)

A complex and parallel pattern of polymorphism for heterochromatic supernumerary segments in the M₇ and S₈ chromosomes has been found in 14 populations of the meadow grasshopperChorthippus parallelus. Nine distinct karyotype classes for these two chromosome pairs occur though they are not equally represented in different populations. Populations differ also with respect to the frequency of supernumerary segments they contain. In all populations the presence of supernumerary segments leads to a significant elevation of mean cell chiasma frequency compared to individuals from the same population lacking such segments. The extent of the effect appears to differ in different populations. The observed frequencies of S₈ karyotypes conform to the expectations of a Hardy-Weinberg distribution. Those of the M₇, however, do not, and in all but one of the 14 populations there is a significant excess of homokaryotypes. In the Ashurst population 26% of the individuals sampled were characterised by germ-line polysomy for the M₄ chromosome, either in the form of entire tetrasomics or more usually as mosaics ranging from tri- to hepta-somics. In all these polysomics the M₄ chromosomes in excess of two were regularly heteropycnotic at first meiotic prophase from zygotene to diakinesis. As a consequence of this multivalents are rare. Extra M₄ chromosomes do not modify the chiasma characteristics of the other chromosomes in the complement. Nor do they modify the action of the supernumerary segments in any way.     

The supernumerary segment system of Stethophyma

Three species of the genus Stethophyma carry supernumerary heterochromatic segments. The European species, S. grossa, has segments located close to the centromere on the S₁₁ chromosome pair, while the North American species, S. lineatum and S. gracile, have both interstitial and terminal segments on the S₁₀ and S₁₁ chromosomes. The latter species show a high degree of segment variation between individuals and the interstitial segments also show variation in size. The presence of segments on the S₁₀ and S₁₁ chromosomes, whether homozygous or heterozygous, modifies the pattern of chiasma distribution in these chromosomes when compared with that found in the basic homozygotes. When interstitial, they also lead to a high frequency of ring bivalents.Two points suggest that interstitially located supernumerary segments may prove to be more common than has previously been accepted. Firstly, combined equational and reductional segregation in unequal bivalents is only otherwise explicable in terms of chiasma formation in a short arm. Secondly the rod chromosomes of many Acridids may well be telocentric as in the case under study.It is proposed that these segments have arisen through a process of duplication with no evidence of interchromosomal movement.On educational leave from the Forest Research Laboratory, Canadian Forestry Service, Fredericton, New Brunswick, Canada.     

Spontaneous chromosome mutations in Truxaline grasshoppers

Three distinct mutant conditions are described in single male individuals from three species of short horn grasshopper. Of these, one is an entire germ line mutant of Myrmeleotettix maculatus, heterozygous for a centric fusion between single M₄ and M₅ telocentric chromosomes. In contrast, the remaining two mutants are present in mosaic form. One is heterozygous for an L₁-M₄ interchange in Omocestus viridulus, the other tetrasomic for the M₄ chromosome in Chorthippus parallelus which in addition is characterised by the inclusion of a supernumerary heterochromatic segment on one S₈ homologue. Centric fusion in Myrmehotettix maculatus has neither disturbed the chiasma potential of the elements constituting the fusion multiple nor, has it apparently influenced the production of balanced gametes. The pattern of chiasma formation in the L₁-M₄ interchange multiple lends support to the contention that the process of chiasma formation originates near the distal end of chromosome arms in Omocestus viridulus. There is no interaction between the two mutant conditions of tetrasomy and the presence of supernumerary segments in Chorthippus parallelus. Moreover, because of the precocious nature of two of the four M₄ homologues there is little tendency to form multivalents. The two M₄ bivalents share a similar mean chiasma frequency.     

The supernumerary segment system of Stethophyma

Three species of the genus Stethophyma have been cytologically examined and all three show variation both for supernumerary heterochromatic segments and for the distribution of standard heterochromatin among the autosomes. The European species, S. grossum, for example, shows considerable interpopulation variation for standard heterochromatin while two of the populations, from Spain and Austria, show supernumerary segment polymorphism. The segments are located interstitially on the S₁₁ chromosome but occupy different positions in the different populations. — In all species, the presence of the extra heterochromatic segments increases the mean chiasma frequency. Moreover, the influence of the segments upon mean chiasma frequency is different in different populations and in different species. In the Spanish population, the increase is both intra- and interchromosomal whereas in Austria the influence of the segment is completely interchromosomal. — In the American species, S. gracile and S. lineatum, where supernumerary heterochromatic segments are carried on both S₁₀ and S₁₁ chromosomes, the effect on chiasma frequency shows a dosage relationship, an increase in the number of segments per individual being correlated with an increase in mean chiasma frequency. It is suggested that the interstitial segments found in all species have originated by direct duplication of chromosome material. By contrast the terminal segments in S. lineatum and S. gracile may be derived by translocation from a B-chromosome since such a chromosome has been found in one individual of the former species. — The variation in segment structure and the distribution of standard heterochromatin, among the European species of S. grossum suggests that these systems have evolved independently in different populations.On educational leave from the Forest Research Laboratory, Fredericton, N. B. Canada.     

Parallel polymorphism for supernumerary segments in Chorthippus parallelus (Zetterstedt)

Heterochromatic supernumerary segments, present in either or both the M₇ and the S₈ chromosomes of the Ashurst (AS) population of Chorthippus parallelus, lead to a significant elevation in mean cell chiasma frequency. This effect appears to be dosage independent within both the S₈ and the M₇ karyomorphs when these are considered separately. Neither is there any marked interaction between the two systems when they are combined with one another. The selective factors controlling the distribution of S₈ karyomorphs within the population appear, however, to act quite independently of those which regulate the M₇ karyomorph pattern. This is revealed in two ways. First, whereas the frequency of S₈ karyomorphs conform to the expectations of a Hardy-Weinberg distribution those of the M₇ do not. Secondly, though the pattern of distribution of S₈ types is uniform throughout the AS population that of the M₇ is not. This heterogeneity of M₇ karyomorphs implies that the population is in some way internally stratified in terms of its breeding structure.     

Parallel polymorphism for supernumerary segments in Chorthippus parallelus (Zetterstedt)

French populations of Chorthippus parallelus like those from Britain are polymorphic with respect to supernumerary segments on the M₇ and S₈ chromosomes. The pattern of polymorphism parallels that of British material on both morphological and behavioural grounds. It agrees also in its effect on mean cell chiasma frequency and the absence of any effect on between cell variance. Finally the agreement extends also to the distribution of karyotypes within populations, those of the S₈ showing a Hardy-Weinberg distribution whereas those of the M₇ show a deficiency of structurally heterozygous types. All these parallels imply a common origin for the British and French material, an origin which, so we must suppose, antedated the physical separation of Britain and France some 8,000 years ago.     

Parallel polymorphisms for supernumerary heterochromatin in Dichroplus elongatus (Orthoptera):

Natural populations of Dichroplus elongatus often exhibit diverse forms of supernumerary heterochromatin. In Tafi Viejo, Tucumán (Argentina), parallel polymorphisms for extra segments on pairs M₆, S₉ (proximal) and S₁₀ (distal) and a mitotically unstable B chromosome were detected. The segments produce intrachromosome effects excluding chiasmata from their neigbourhood and displacing them to regions distal to the extra heterochromatin. The individuals bearing simultaneously the B and the segment on M₆ show a decrease in the frequency of interstitial chismata (X_i) while those carrying only segments on M₆ or S₁₀ have an increase of this variable when compared with standard males. The between cell variance of X_i is also higher in M₆ segment carriers. B individuals present an increase of abnormal spermatid frequency which may be explained by the simultaneous occurrence of two mechanisms: 1) lagging of supernumeraries and 2) physiological effects of B's affecting the meiosis even in cells lacking them. The intra and interchromosome effects may be important for the plasticity of populations allowing recombination to explore new chromosome regions. The B polymorphism seems to be stable which points to an advantage of B carriers and/or the occurrence of accumulation mechanisms counterbalancing their negative effects on fertility.     

SUPERNUMERARY CHROMOSOMES IN SAXIFRAGA VIRGINIENSIS (SAXIFRAGACEAE)

Acetocarmine squashes of root tips have demonstrated that 2n = 20 and 38 in Saxifraga virginiensis. These contrast with the earlier reported count of 2n = 28 for this species. In several populations supernumerary chromosomes were detected. Both intrapopulational and interpopulational variation in supernumerary chromosome number were detected, with the largest number of supernumerary chromosomes observed being six. Because these supernumerary chromosomes are equal in size to many of the smaller A chromosomes during mitotic metaphase, the presence of supernumerary chromosomes in this species could not be ascertained by analysis of mitotic metaphase preparations alone. During mitotic prophase, however, the supernumerary chromosomes of S. virginiensis are highly heterochromatic, appearing more densely coiled and darkly stained than the A chromosomes. This characteristic facilitated the recognition of supernumerary chromosomes in this species. The similarity in size of A and supernumerary chromosomes during mitotic metaphase and the observation of six supernumerary chromosomes in one population suggest that the count of 2n = 28 reported earlier for S. virginiensis may actually be a misinterpretation of 2n = 20 plus 8 supernumerary chromosomes. Furthermore, these findings and the observation of this same supernumerary chromosome phenomenon in other species of Saxifraga raise the possibility that some of the many disparate chromosome counts attributed to aneuploidy in the large genus Saxifraga may also be the result of misinterpretations of supernumerary chromosomes as A chromosomes.     

Non-random segregation during anaphase II in an individual of Arcyptera tornosi (Bol.) (Orthoptera) heterozygous for three supernumerary heterochromatic segments

An individual of Arcyptera tornosi heterozygous for distal heterochromatic segments affecting M₆, S₁₀ and S₁₁ chromosomes has been analyzed during all the meiotic stages in order to establish the pattern of meiotic segregation in anaphase I and II. S-bivalents invariably show an equational separation during anaphase I and the anaphase II separation is non-random, both chromatids with heterochromatic segments often segregating to the same pole. Differences are significant if compared with the expected segregation. Some aspects of this particular chromosome behaviour are briefly discussed.     

Extra heterochromatin in natural populations of Gomphocerus sibiricus (Orthoptera: Acrididae)

Two types of extra heterochromatin, in the form of either supernumerary segments or B-chromosomes, have been observed in natural populations of Gomphocerus sibiricus. The presence of a heterochromatic supernumerary segment affecting the M₇ pair in a population from the Valle de Arán disturbs the normal separation of this bivalent at anaphase I of meiosis and non-disjunction products, respectively deficient or duplicate for the M₇, are present at metaphase II.A stable B_m chromosome has been detected in a second population from Formigal. In a single individual where a B_m is present together with a small unstable B_s supernumerary chromosome both the B_m and the M₅ are unstable in the germ line and in the case of the M₅ this unstability leads to a state of germ line polysomy.     

Supernumerary segments in five species of grasshoppers (Orthoptera: Acridoidea)

Supernumerary segments have been observed in five species of grasshoppers: Calliptamus barbarus, Oedipoda fuscocincta, Acrotylus insubricus, Omocestus raymondi and Chorthippus ariasi. In four cases they are located in the S-chromosomes, but in A. insubricus they are carried by the megameric pair (M₉). In C. barbarus and O. fuscocincta we have observed non-homologous association during diplotene between the extra segments and the X-chromosome. The supernumerary segments of these two species are distally located. However, in anaphase-I the unequal bivalents divide reductionally in 30% and 20% of the cells, respectively. Finally, the supernumerary segments of C. barbarus do not produce any effect on mean chiasma frequency, but they decrease significantly the between-cell variance of chiasmata in males carrying them.     

Effects of different supernumerary segments on chiasma distribution of the polymorphic species Chorthippus jucundus (Orthoptera: Acrididae)

The analysis of 18 wild populations of the polymorphic species Chorthippus jucundus has revealed the presence of five distal extra segments. They differ in location, size and staining properties. Two of them (L₁H and L₁h) are located in the largest element and do not C-band, while the remainder (S₈H, S₈h and S₈h₁) appear in the shortest chromosome and show positive C-banding. Those located in the same chromosome differ basically in their size. However, any of these blocks induce a similar change in the pattern of chiasma distribution within the affected bivalent. Additionally four patterns of C-banding as regards the presence of distal bands in some autosomes have been detected in the different populations.     

Response of Barley Lines with Structural Rearrangements in Chromosomes 5, 6 and 7 to Limited Nitrogen Nutrition

The responses of barley (Hordeum vulgare L.) lines with rebuilt chromosomes 5, 6 and 7 to reduced nitrogen nutrition were evaluated in juvenile growth stages. The material included two series of duplications (D) produced in the short arm of chromosome 6 and of chromosome 7, and in the long arm of chromosome 5 and of chromosome 6; their parental translocation lines (T) - from which analyzed duplications were derived and a standard karyotype cv. Bonus as a control. The translocation lines have break points located in 6_S and 7_S, or 5_L and 6_L. Only the lines with duplicated segments of the short arms of satellited (6 and 7) chromosomes exhibited an improved tolerance to reduced nitrogen supply. No changes relative to cv. Bonus were observed in the T-lines. More tolerant D-lines showed lower stimulation of the root development. Obtained results suggests that the adaptability factors for the low N tolerance at the vegetative growth stage of barley are located in the short arms of 6 and 7 chromosomes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Meiotic drive against an autosomal supernumerary segment promoted by the presence of a B chromosome in females of the grasshopper Eyprepocnemis plorans

Twenty-seven out of 50 progeny analyses performed with specimens of the grasshopper Eyprepocnemis plorans were informative about the transmission of a supernumerary heterochromatic chromosome segment. The simultaneous presence of a B chromosome in some of the parents involved in the crosses permitted us to test the relationship between both types of supernumerary heterochromatin with respect to their transmission. The results demonstrated that the supernumerary segment is partly eliminated through females possessing B chromosomes. The implications of this in relation to the occurrence of the extra segment in natural populations are discussed.by S.A. Gerbi     

A cytogenetic analysis in Psophus stridulus (L.) (Orthoptera: Acrididae): B-chromosomes and abnormal spermatid nuclei

The male chromosome complement of Psophus stridulus (L.) (Orthoptera: Acrididae) has been analyzed by using orcein staining, C-banding and silver impregnation. During spermatogenesis only one pair of autosomes (M₉) shows an active nucleolar organizer region located in a C-banded constriction. There are other chromosome pairs with constrictions but these do not show nucleolar activity. The relationship between these constrictions and the C-banding pattern exhibited by this species is analyzed.In a sample of 83 males from five populations, two different supernumerary chromosomes were observed. Four males had a metacentric B-chromosome (B^m) similar in size to the sex chromosome and mitotically stable. Its meiotic behaviour indicates that it is an isochromosome. An additional small B-chromosome (B⁸) was also found in a single follicle of one individual carrying the B^m.A high rate of abnormal spermatids (macrospermatids) was scored in the individuals carrying B's. This proportion is notably higher in the follicle containing both the B^m and the B⁸.     

Fragment chromosomes in Myrmeleotettix maculatus (Thunb.)

Structural changes involving fragmentation and the deletion of chromosome material have resulted in the production of morphological variants of the standard B chromosomes of Myrmeleotettix maculatus. Three distinct types are described — a considerably reduced B^st chromosome with a sub-terminal centromere and a large and small telocentric fragment. In addition, the B^st chromosome can itself give rise to a small telocentric fragment. The fact that such telocentric fragments have been found only in mosaic germ lines implies a lack of stability and an inability to perpetuate themselves between generations. The non-reciprocal translocation of one such fragment onto the short arm of a metacentric autosome does little to improve the efficiency of its transmission from one generation to another. The behaviour of autosomal fragments, discovered in both the M₆ and S₈ chromosomes of this species, parallels that of B fragments. Only the B^st chromosomes appear both mitotically and meiotically stable.     

Comparative analysis of rDNA location in five Neotropical gomphocerine grasshopper species

We report here, for the first time, the chromosome complement, number and location of the nucleolar organizer regions (NORs) revealed by silver staining (AgNO₃) and fluorescent in situ hybridization (FISH) in five Neotropical gomphocerine species: Rhammatocerus brasiliensis, R. brunneri, R. palustris, R. pictus and Amblytropidia sp. The objective of this study was to summarize available data and propose a model of chromosome evolution in Neotropical gomphocerines. All five species studied showed chromosome numbers consisting of 2n = 23,X0 in males and 2n = 24,XX in females. Amblytropidia sp. was the only species showing a bivalent (M₈) with megameric behavior during meiosis. The rDNA sites were restricted to autosomal pairs, i.e. the pericentromeric region of the S₉ chromosome, the consensus NOR location in all five species. R. brasiliensis was the only species showing additional NORs on M₄ and M₆ pairs which, likewise the S₉ NOR, were active in all cells analyzed. Comparison of these results with those reported previously in Palearctic gomphocerine species suggests higher resemblance of Neotropical species with the Old World species also possessing 23/24 chromosomes. Evolutionary mechanisms responsible for the observed interspecific variation in NOR location in this group are discussed.     

A polymorphism for heterochromatic supernumerary segments in Chorthippus parallelus

Supernumerary heterochromatic segments have been found in the S₈ bivalent of two populations of Chorthippus parallelus. These segments occur both in the heterozygous and the homozygous states. In both populations the frequencies of basic homozygotes, structural heterozygotes and structural homozygotes conform to a Hardy-Weinberg distribution. In the structurally heterozygous and homozygous states there is a significant increase in the chiasma frequency of the bivalents other than the S₈ itself. It is suggested that the adaptive role of these supernumerary segments can be explained in terms of this interchromosomal effect.To Professor J. Seiler in commemoration both of his 80th birthday and his many distinguished years of cytological service.     

Analysis of Linkage Between Biochemical and Morphological Markers of Rye Chromosomes 1R, 2R,and 5R and Mutations of Self-Fertility at the Main Incompatibility Loci

In F₂ hybrids between self-sterile plants of the Volkhova cultivar and self-fertile lines with established self-fertility mutations (sf mutations) at the major incompatibility loci S (1R), Z (2R), and T (5R), the effect of sf mutations on the inheritance of secalin-encoding, isozyme, and morphological markers located on the same chromosomes was investigated. Linkage between loci Prx7 and Sand locus Sec3 coding for high-molecular-weight secalins on chromosome 1R was shown for the first time. The frequency of recombination between Prx7andSec3and between S and Sec3was 29.1 ± 4.8% and 30.9 ± 7.0%, respectively. Independent inheritance of locus Z and isozyme markers of chromosome 2R, Est3/5 and -Glu, from locus Sec2 encoding 75-kDa -secalins was shown; in hybrids, the recombination frequency between Est3/5 and locus Z varied from 19.2 ± 8.1 to 50%. Independent inheritance of morphological (Ddw and Hs) and isozyme markers (Est4, Est6/9,and Aco2) of chromosome 5R from locus Tlocated on the same chromosome was demonstrated.