Changes in NOR activity pattern in the presence of supernumerary heterochromatin in the grasshopper Eyprepocnemis plorans

Nucleolus organizer region (NOR) activity was analysed in four types of males of the grasshopper Eyprepocnemis plorans, possessing two kinds of supernumerary heterochromatin: a B chromosome and a supernumerary chromosome segment proximally located on the smallest autosome (S11). In males lacking extra heterochromatin, the four active NORs located on the S9, S10, S11, and X chromosomes showed independent activity patterns, but several kinds of dependence appeared in the presence of supernumerary heterochromatin. Furthermore, temporal changes in NOR activity were observed during the first 2 weeks of adult life in standard males but not in males carrying supernumerary heterochromatin. It is suggested that all these effects are related to the DNA content of both types of extra heterochromatin.     

Male and female segregation distortion for heterochromatic supernumerary segments on the S8 chromosome of the grasshopper Chorthippus jacobsi

The mode of inheritance of supernumerary segments located on three different chromosome pairs was investigated in controlled crosses with specimens of the grasshopper Chorthippus jacobsi. While extra segments located on chromosomes M₅ and M₆ showed Mendelian inheritance, that on S₈ did not. Thus, the two supernumerary heterochromatic chromosome segments located distally on the S₈ chromosome accumulated through non-Mendelian transmission through both sexes. The observed transmission patterns may be explained by gametic selection for spermatozoa carrying segmented S₈ chromosomes, in addition to meiotic drive for segmented S₈ chromosomes in heterozygous females. The significance of these findings for the maintenance of these polymorphisms in natural populations is discussed.by S.A. Gerbi     

A rare variant of chromosome 1 in the house mouse: the presence of 2 supernumerary heterochromatin segments

An abnormal chromosome 1 with two extra interstitial heterochromatin segments was found in the karyotype of a house mouse from the Maritime Territory. Until recently, variants of the abnormal chromosome 1 with the only extra C-block were known in house mouse of some European populations. Sizes of the abnormal chromosome 1 in a house mouse of the Maritime Territory are increased almost by 50%, in comparison with the normal homologue. C-banding showed that extra segments were localized in the area of D and F segments of the standard karyotype in house mouse, and stained homogeneously.     

Chiasma formation in duplicated segments of the haploid rye genome

In meiosis of haploid rye associations of two or more chromosomes are observed. In order to investigate whether these associations are chiasmate, metaphase I and anaphase I associations were analysed after Giemsa banding. — At anaphase I chromatid exchanges between differently marked chromosome arms were observed, which proved the presence of real chiasmata. The association between banded and unbanded arms shows that the heterochromatic telomeres do not act as secondary pairing sources. Different statistical approaches were used to test randomness of chiasma formation. It appeared to be non-random, which showed that the segments involved were non-randomly located and probably limited in number. The nature of these segments is discussed.     

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     

Effects of B chromosomes and supernumerary segments on morphometric traits and adult fitness components in the grasshopper, Dichroplus elongatus (Acrididae)

The South American species, Dichroplus elongatus, is polymorphic for B chromosomes and supernumerary segments in chromosome pairs M6 (SS6), S9 (SS9) and S10 (SS10). Both forms of supernumerary heterochromatin shape chiasma frequency and distribution and B chromosomes also affect male fertility. Here, we analysed the effects of these polymorphisms on morphometric traits (total, 3rd femur, 3rd tibia, thorax and tegmen lengths) and several adult fitness components, including male and female mating success, and female reproductive potential. B chromosomes tend to decrease, and SS6 segments to increase the body size of carriers. The analysis of reproductive potential suggested that B chromosome carrying females have higher numbers of embryos per clutch and ovarioles per ovary. The uni- and multivariate analysis of mating success revealed that sexual selection favours larger individuals of both sexes and males with standard karyotype. B chromosomes may have accumulation mechanisms, which involve preferential transmission of B chromosomes to germ cells or functional gametes. The maintenance of Bs might be explained by interactions among accumulation mechanisms and trade-offs between detrimental and favourable effects on different fitness components.     

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.     

Undertransmission of a supernumerary chromosome segment through heterozygous females possessing B chromosomes in the grasshopper Eyprepocnemis plorans.

The transmission ratio (ks) for a supernumerary chromosome segment was studied in a total of 54 heterozygous females collected from two Spanish natural populations of the grasshopper Eyprepocnemis plorans. Our analysis clearly demonstrated that ks is negatively dependent on the number of B chromosomes in the female. The possible mechanisms by which B chromosomes may cause undertransmission of the supernumerary segment, and the implications of this phenomenon for the maintenance of this extra chromosome segment, are discussed.     

Molecular cytogenetic analysis of supernumerary heterochromatic segments in Rumex acetosa.

The dioecious plant Rumex acetosa shows intraspecific karyotype variation, caused by supernumerary heterochromatic segments or DAPI (4',6-diamidino-2 phenylindole)-bands at the ends of the short arms of three pairs of autosomes. A DNA sequence (RAE730) specific to the supernumerary heterochromatic segments was cloned and sequenced. RAE730 was about 730 bp and AT-rich (71% AT-content). Using fluorescence in situ hybridization (FISH), RAE730 was localized in the supernumerary DAPI-positive heterochromatic segments on several mitotic chromosomes and chromocenters in interphase nuclei, but not in the DAPI-bands of Y or B chromosomes. RAE730 was tandemly arranged in the genome, and the copy number varied between plants from 40000 to 304000 copies per 2C, corresponding to the relative amount of supernumerary heterochromatic segments per genome. These results indicate that the karyotype variation caused by the supernumerary heterochromatic segment was generated by amplification or reduction of the tandem repeats of RAE730.     

Meiotic mutants of rye Secale cereale L. II. The nonhomologous synapsis in desynaptic mutants sy7 and sy10

We studied the expression and inheritance of two spontaneous mutations found in different populations of rye Secale cereale L. that cause high univalent frequency in meiosis and low fertility. Both mutations were inherited as monogenic recessives. For each of the mutations the corresponding gene symbols (sy7 and sy10) were suggested although their allelism has not been studied. These mutants differ in chiasma frequency and in the number of univalents per meiocyte. Electron microscopy of the wholemount surface-spread synaptonemal complexes (SCs) from microsporocytes of both mutants revealed that during meiotic prophase I random synapsis began and progressed that involved not only homologous but also nonhomologous chromosomes. SCs were formed with frequent changes of pairing partners (switches) and intrachromosomal foldbacks of unpaired axial elements. As a result, incompletely synapsed, non-homologous and multivalent SCs were formed in mutants by the stage analogous to pachytene in normal plants. In sy7 a maximum in the number of switches and foldbacks were observed at zygotene, whereas in sy10 this occurred at pachytene. We suggest that it is the process of recognition of homology that is impaired in both mutants. This leads to indiscriminate synapsis and prevents chiasma formation. Both mutants may be classified as desynaptic.     

Distortional meiotic segregation of a supernumerary chromosome producing differential frequencies in the sexes in the short-horned grasshopper Phaulacridium vittatum

Samples of males reveal the presence of a large, mitotically stable supernumerary chromosome in five populations examined. A stable frequency (11.22±0.3%) of male carriers has been observed over nine years in one population. The supernumerary follows closely the condensation cycle and behaviour of the sex chromosome in spermatogonial mitosis and meiosis. A structure simulating a terminalized chiasma frequently joins the precocious sex and supernumerary chromosomes during meiotic prophase; these two chromosomes move preferentially (70%) to opposite poles during the subsequent stages producing a differential transmission of the supernumerary to the two sexes. It is possible that the stable frequency in the population is maintained by a conserved balance between the two sexes without the need of an elimination system. The evidence supports the interpretation that the supernumerary chromosome is partially homologous with the sex chromosome. The possibility that the supernumerary might evolve into a neo-Y chromosome is suggested.     

Limited condition dependence of male acoustic signals in the grasshopper Chorthippus biguttulus

In many animal species, male acoustic signals serve to attract a mate and therefore often play a major role for male mating success. Male body condition is likely to be correlated with male acoustic signal traits, which signal male quality and provide choosy females indirect benefits. Environmental factors such as food quantity or quality can influence male body condition and therefore possibly lead to condition-dependent changes in the attractiveness of acoustic signals. Here, we test whether stressing food plants influences acoustic signal traits of males via condition-dependent expression of these traits. We examined four male song characteristics, which are vital for mate choice in females of the grasshopper Chorthippus biguttulus. Only one of the examined acoustic traits, loudness, was significantly altered by changing body condition because of drought- and moisture-related stress of food plants. No condition dependence could be observed for syllable to pause ratio, gap duration within syllables, and onset accentuation. We suggest that food plant stress and therefore food plant quality led to shifts in loudness of male grasshopper songs via body condition changes. The other three examined acoustic traits of males do not reflect male body condition induced by food plant quality.     

Condition‐dependence and sexual ornamentation: Effects of immune challenges on a highly sexually dimorphic grasshopper

Sexual ornaments contribute substantially to phenotypic diversity and it is particularly relevant to understand their evolution. Ornaments can assume the function of signals‐of‐quality that the choosy sex uses to evaluate potential mating partners. Often there are no obvious direct benefits and investment into mate choice is primarily rewarded by beneficial alleles that are inherited to the offspring. Inter‐sexual communication via sexual ornaments requires honesty of the sexual signal, yet the question of what maintains honesty remains only partially solved. One solution is that honesty is maintained by trait expression being dependent on individual condition, since condition‐dependent trait expression offers an effectively inexhaustible source of genetic variability. Here we test in the highly sexually dimorphic club‐legged grasshopper Gomphocerus sibiricus if putative sexual ornaments, in particular the striking front‐leg clubs, are more strongly affected by a lipopolysaccharide (LPS) immune challenge than putatively not sexually selected traits. Our results show overall little condition‐dependent expression of morphological and song traits, with sexually selected traits exhibiting effects comparable to nonsexually selected traits (with the possible exception of stridulatory file length and syllable‐to‐pause ratio in advertisement songs). Interestingly, field observations of individuals of lethally parasitized individuals suggest that a very strong environmental challenge can specifically affect the expression of the front‐leg clubs. The presence of 1% of males in natural populations with missing or heavily deformed clubs plus 5% with minor club deformations furthermore indicate that there are risks associated with club development during final ecdysis and this might act as a filter against deleterious alleles.     

Rhinovirus multistranded RNA: dependence of the replicative form on the presence of actinomycin D.

The multistranded and double-stranded RNAs synthesized in HeLa cells infected with rhinovirus in the presence and in the absence of actinomycin D have been characterized by polyacrylamide gel electrophoresis and hybridization studies. The replicative form is only found in infected cells treated with actinomycin D, whereas the replicative intermediate is found in both the presence and the absence of the drug. The significance of these results is discussed.     

Temporal frequency stability and absence of effects on mating behaviour for an autosomal supernumerary segment in two natural populations of the grasshopper Eyprepocnemis plorans.

Interannual evolution of a polymorphism for a supernumerary segment in the smallest autosome of the grasshopper Eyprepocnemis plorans has been analysed in two natural populations. The polymorphism seemed to be stable in both populations, despite its undertransmission through heterozygous females carrying B chromosomes. Analyses of the effects of the extra segment on mating behaviour failed to show differential mating success in any sex or consistent effects on mating pattern. These results are discussed in relation to the maintenance of this polymorphism in natural populations.     

Genetic control of chromosomal synapsis in Secale cereale L. rye meiosis: sy19 gene, causing heterologous synapsis

Analysis of manifestation and inheritance of a new mutation inducing irregular synapsis in rye showed that abnormal phenotype is determined by a recessive allele of the sy19 gene. In the homozygotes for this mutation, even at the light microscopic level, abnormal formation of bivalents is already observed at pachytene-diakinesis. At metaphase I, the univalent frequency varies from 0 to 14; in a few cells, multivalent associations of chromosomes, which are not clearly oriented in the spindle, are detected. Electron microscopy of synaptonemal complexes revealed both homologous and heterologous synapsis in homozygotes for sy19, namely partial loss of the ability to stringent homology search. Analysis of joint inheritance of sy19 and asynaptic sy1 mutations showed that they are nonallelic, inherited independently, and interact by recessive epistasis. The phenotype of double sy1sy19 mutants indicates that the sy19 gene conditioning heterologous synapsis operates at meiosis later than the synaptic gene sy1. The epistatic group of mutations, sy9 > sy1 > sy19 and sy3, was determined.