Comparative allozyme analysis of two geographic populations of Pararcyptera microptera meridionalis in China

The genetic structure of the two populations of Pararcyptera microptera meridionalis (Ikonn.) from Hebei and Liaoning in China was analyzed with horizontal starch gel electrophoresis. Among 15 loci of 11 enzymes identified in zymograms, Adk-1, Fbp-1, Mdh-2 and G3pd-1 showed low variability with few alleles. Higher allelic polymorphisms were observed at Fbp-2, Mdh-1 and Me-1. The two populations demonstrated high percentage of polymorphic loci (93.3% and 100.0%) but low observable overall heterozygosity (0.061 and 0.086), that could be attributed to heterozygote deficiencies, which led to the genotype frequency deviating from Hardy-Weinberg expectations. It is reasoned that the strong movement capability of the insect makes the individuals likely to be exposed to drastically varied environments, which tends to maintain dynamic equilibrium of genetic polymorphisms. The F-statistics between the two populations was comparatively smaller ( F(st) = 0.084), but larger when compared with those in migratory locusts like Locusta migratoria manilensis. Nei's genetic identity (I) and Roger's genetic distance (D) also showed close genetic relationship of the two populations by their high genetic identity (I = 0.904) and small genetic distance (D = 0.256). However,considerably qualitative and quantitative differences were noted at loci Acp-1 (F(st) = 0.462) and Pgi-1 (F(st) = 0.182).

[Molecular phylogeny of some species of the acridoidea based on 16S rDNA]

Based on the 16S rDNA of 8 species (belonging to 8 families of Acridoidea) from China and keyed to 8 relative species of Orthoptera from GenBank, the homologus sequences were compared. The used frequency of nucleotide was calculated and the molecular phylogenetic tree constructed by MEGA microsoft. In the 480 bp fragment of mitochondial 16S rDNA, A + T was about 70.7% and G + C only 29.3%. The sequence data revealed considerable variation in 188 nucleotide sites among the analyzed individuals from 8 different families. The variation rate of transversion was larger than or approach to transition. The results showed that the ranges of the 16S rDNA nucleotide divergence within species, among species of a genus, among genera of a family, and among the same family and suborder were 1.5%, 3.5%-3.6%, 4.8%-15.8% and 15.2%-25.6%, respectively. The members of the same genus and family were grouped together. The phylogenetic relationships of 8 families were Pyrgomorphidae-->Chrotogonidae-->Pamphagidae-->Oedipodidae-->Acrididae--> Arcypteridae-->Gomphoceridae-->Catantopidae. Pyrgomorphidae had closer relationships with Chrotogonidae as well as being the most ancestral group. Arcypteridae and Gomphoceridae were the sister groups and had closer relationships with most evolutionary Catantopidae. Tridactylidae was divided firstly as a suborder, which differs from the recent taxonomy distinctly. Haglidae (Tettigonoidea) and Gryllidae were grouped into suborder Ensifera, Tetrigidae and 8 families of Acridoidea were grouped into suborder Caelifera, as same as recent taxonomy.

Cytological and morphological differences between two species of the genus Tettigonia (Orthoptera, Tettigoniidae) from Korea

Tettigonia ussuriana and T. dolichopoda maritima differ in the length of tegmina, details in venation, and in females in details of the subgenital plate. The two species of the genus Tettigonia have the same number and morphology of autosomes but a different morphology of the X chromosome: in T. ussuriana it is metacentric, whereas in T. dolichopoda maritima acrocentric. In both species, euchromatic zones and breaks of one or to chromatids during meiosis and mitosis in the X chromosome were observed. Additionally, B chromosomes were noted in most individuals of both species.

A comparison of five hybrid zones of the weta Hemideina thoracica (Orthoptera: Anostostomatidae): degree of cytogenetic differentiation fails to predict zone width

Tension zones are maintained by the interaction between selection against hybrids and dispersal of individuals. Investigating multiple hybrid zones within a single species provides the opportunity to examine differences in zone structure on a background of differences in extrinsic factors (e.g., age of the zone, ecology) or intrinsic factors (e.g., chromosomes). The New Zealand tree weta Hemideina thoracica comprises at least eight distinct chromosomal races with diploid numbers ranging from 2n = 11 (XO) to 2n = 23 (XO). Five independent hybrid zones were located that involve races differing from one another by a variety of chromosomal rearrangements. The predicted negative correlation between extent of karyotypic differentiation (measured in terms of both percent of genome and number of rearrangements) and zone width was not found. Conversely, the widest zones were those characterized by two chromosome rearrangements involving up to 35% of the genome. The narrowest zone occurred where the two races differ by a single chromosome rearrangement involving approximately 2% of the genome. The five estimates of chromosomal cline width ranged from 0.5 km to 47 km. A comparative investigation of cline width for both chromosomal and mitochondrial markers revealed a complex pattern of zone characteristics. Three of the five zones in this study showed cline concordance for the nuclear and cytoplasmic markers, and at two of the zones the clines were also coincident. Zones with the widest chromosomal clines had the widest mitochondrial DNA clines. It appears that, even within a single species, the extent of karyotypic differentiation between pairs of races is not a good predictor of the level of disadvantage suffered by hybrids.

Fission or fusion? Mitochondrial DNA phylogenetics of the chromosome races of Hemideina crassidens (Orthoptera: Anostostomatidae)

The weta Hemideina crassidens has two chromosomal races that differ by two centric fusions or fissions. The mitochondrial DNA of weta from both chromosomal races and a sister species were sequenced for a 750-bp region of the gene coding for cytochrome oxidase I. The average pairwise genetic distance among the 15 (XO)-chromosome race weta was almost four times greater than the average distance among the 19 (XO)-chromosome race weta. The weta from the 19-chromosome race formed a well-supported monophyletic clade in all shortest maximum parsimony trees. Maximum likelihood and neighbor-joining trees suggested that the 15-chromosome karyotype was paraphyletic with respect to the 19-chromosome karyotype, but this was not supported by maximum parsimony analyses. Although phylogenetic analysis could not exclude chromosome fusion as the rearrangement responsible for the karyotype differentiation, the level of sequence variation and pattern of distribution appear to implicate fission as the more likely event.

C-heterochromatin pattern of ten species of tetrigids (Tetrigidae, Orthoptera)

The karyotypes of species belonging to the Tetrigidae is characterised by structural conservatism. The standard chromosome set of T. japonica, T. simulans, T. bolivari, P. meridionalis, U. depressus, and F. robustus consists of 2n = 13 acrocentric chromosomes in males and 2n = 14 in females, with a sex determining mechanism of X0 male and XX female. C-bands distribution often species belonging to 4 genera were studied. Differences in the position of C-bands and number of chiasma between species are discussed.

Centrosome dynamics and inheritance in related sexual and parthenogenetic Bacillus (Insecta Phasmatodea)

In animals, some general features of centrosome dynamics and inheritance have been widely recognized. The most acknowledged model assigns to sperm the contribution of a centriole to the fertilized egg, which in turn provides the pericentriolar materials, including gamma-tubulin, recruiting them from the cytoplasm: the main zygote microtubule organizing center (MTOC) is thus reconstituted to organize first the spermaster and then the full first embryonic spindle. Obviously the model cannot apply to parthenogenetic systems, which actually rely on egg components alone. In stick insects of the Bacillus genus, the spindle of both somatic and germ cells is clearly anastral, therefore we have been investigating their centrosome in sexual and parthenogenetic taxa by analyzing its component dynamics and transmission through the use of monoclonal beta- and gamma-tubulin antibodies and transmission electron microscopy (TEM). It has been shown that in sexually reproducing species the spermatozoon does not contribute the centriole, so that the egg wholly provides the MTOC and the ensuing anastral spindle of the embryo: MTs appear to derive from pronuclear chromatin surroundings and no asters are observed. The parthenogenetic embryo development is the same as the sexual one if syngamy is excepted. The parthenogenetic mechanism realized by these panoistic insects appears to differ from that observed in the meroistic hymenopteran and drosophilid species, where the embryo spindle derives from asters formed in the egg cortex. In stick insects, the lack of sperm contribution to embryonic centrosome appears to be a major trait accounting for the widespread occurrence of facultative and obligate parthenogenesis within the order.

Chromosome inversion polymorphisms influence morphological traits in Trimerotropis pallidipennis (Orthoptera)

Trimerotropis pallidipennis is a New World grasshopper whose South-American populations are polymorphic for six pericentric inversions. Previous work has demonstrated that the frequences of these inversions correlate with climatic variables, and hence a possible adaptive pattern was put forward. In the present work we analysed a sample of a natural population of T pallidipennis to ascertain whether the chromosomal inversions have effects on exophenotypes. Two hundred and sixty-eight males coming from a natural population at Uspallata, Mendoza Province, Argentina were analysed, and it was observed that most inversions had significant effects on phenotypes. Furthermore, some body size-related characteristics (such as tegmina length) were correlated with the number of inversions. Individuals from populations at higher altitude or latitude (i.e., at lower minimum temperatures), along with higher frequencies of standard sequences, were significantly smaller, and this coherence between interpopulational with intrapopulational results may indicate that the diminished body size of the standard sequence-carrying individuals may be caused by an effect of the inversions, or genes within the inversions, on body size. We finally put forward the hypothesis that reduced body size in a context of reduced minimum temperature may be a response to shortened development season, and so smaller individuals may be advantageous.

Chromosomal polymorphism, morphological traits and male mating success in Leptysma argentina (Orthoptera)

Leptysma argentina (Acrididae: Orthoptera) is polymorphic for a centric fusion between pairs 3 and 6 of its basic chromosomal complement. With the aim of carrying out an analysis of selection components in this species, male mating success, in relation to karyotype and three morphometric traits, was assessed by using experimental contests with four males and one female per mating cage. Karyotype was assessed in terms of fused chromosome 3/6 dosage and coded as "0", "1" and "2" for unfused homozygotes, heterozygotes and fusion homozygotes, respectively. The individual ANOVA showed significant differences between "successful" and "unsuccessful" males in all four measured characters. Fusion carriers showed a higher relative fitness. Since the phenotypic correlations among traits were significant, the selective effects were assessed by means of a multivariate analysis, which demonstrated that selection acted significantly on femur length only, selection on karyotype being indirect. Given that the fusion frequency has been constant since 1985, the presence of selective trade-offs cannot be ruled out.

Estimating genetic correlations in natural populations in the absence of pedigree information: accuracy and precision of the Lynch method

Usually, genetic correlations are estimated from breeding designs in the laboratory or greenhouse. However, estimates of the genetic correlation for natural populations are lacking, mostly because pedigrees of wild individuals are rarely known. Recently Lynch (1999) proposed a formula to estimate the genetic correlation in the absence of data on pedigree. This method has been shown to be particularly accurate provided a large sample size and a minimum (20%) proportion of relatives. Lynch (1999) proposed the use of the bootstrap to estimate standard errors associated with genetic correlations, but did not test the reliability of such a method. We tested the bootstrap and showed the jackknife can provide valid estimates of the genetic correlation calculated with the Lynch formula. The occurrence of undefined estimates, combined with the high number of replicates involved in the bootstrap, means there is a high probability of obtaining a biased upward, incomplete bootstrap, even when there is a high fraction of related pairs in a sample. It is easier to obtain complete jackknife estimates for which all the pseudovalues have been defined. We therefore recommend the use of the jackknife to estimate the genetic correlation with the Lynch formula. Provided data can be collected for more than two individuals at each location, we propose a group sampling method that produces low standard errors associated with the jackknife, even when there is a low fraction of relatives in a sample.

Some aspects of karyotype of Liarina (Orthoptera: Tettigoniidae, Agraeciini) from Vietnam

Karyotypes (chromosome number and shape) of four species of the subtribe Liarina were studied. The chromosome numbers and NF (Fundamental Number) in this group of species range from 2n Male = 33 (34) to 27(30): Liaromorpha buonluoiensis 2n Male = 33 (34), Sialaiana transiens 2n Male = 29 (34), Liara tramlapensis 2n Male = 29 (32), and Anelytra (Perianelytra) propria 2n Male = 27 (30). Cyto-taxonomy analysis indicates an intensive karyotype evolution among species belonging to three different groups of the genera. Differences of karyotypes are connected with Robertsonian fusion and tandem fusion in autosomes. Additionally, C-banding distribution and location of the NORs were studied.

Chromosome evolution in the genus Poecilimon (Orthoptera, Tettigonioidea, Phaneropteridae)

Cytotaxonomic analysis of 20 species and subspecies of the genus Poecilimon using C-banding pattern, chiasma frequency, and morphometric characteristics of the chromosomes were described. Using a cladistic analysis the chromosome data provided a basis to produce a phylogenetic tree which was compared with a tree based on morphological characters and DNA sequence data. There are important differences in the grouping of data sets to species obtained on the basis of morphology/DNA analyses and that based on chromosomes. The explanation of the differences between C-banding patterns and taxonomic proximity is probably that the C-banding pattern changes quickly as the result of the high degree of variation of constitutive heterochromatin.

Chromosome races with Pliocene origins: evidence from mtDNA

There are eight distinct chromosomal races of the New Zealand weta Hemideina thoracica. We used mtDNA sequence data to test the hypothesis that these races originated on islands during the early Pliocene (7--4 million years ago). Nine major mitochondrial lineages were identified from 65 cytochrome oxidase I sequences. Phylogenetic analysis of these lineages suggests that they arose at approximately the same time. The geographical distribution of some lineages coincides with areas that were islands during the Pliocene. Overall, hierarchical AMOVA analysis shows that chromosomal races and Pliocene islands describe only 28% and 24%, respectively, of the total current mtDNA variation. However, removing one widespread (A) and one putatively introgressed (F) lineage increases these estimates to 65% and 80%, respectively. Intraspecific sequence divergence was very high, reaching a maximum of 9.5% (uncorrected distance) and GC content was high compared to other insect mtDNA sequences. Average corrected distance among mtDNA lineages supports the Pliocene origins of this level of genetic diversity. In the southern part of the species range there is reduced mtDNA variation, probably related to local extinction of H. thoracica populations from recent volcanic activity and subsequent re-colonization from a leading edge. In contrast, in this southern part there are five chromosome races, suggesting that chromosome races here may be younger than those in the north.

Pondering the procephalon: the segmental origin of the labrum

With accumulating evidence for the appendicular nature of the labrum, the question of its actual segmental origin remains. Two existing insect head segmentation models, the linear and S-models, are reviewed, and a new model introduced. The L-/Bent-Y model proposes that the labrum is a fusion of the appendage endites of the intercalary segment and that the stomodeum is tightly integrated into this segment. This model appears to explain a wider variety of insect head segmentation phenomena. Embryological, histological, neurological and molecular evidence supporting the new model is reviewed.

Characterization of a hybrid zone between two chromosomal races of the weta Hemideina thoracica following a geologically recent volcanic eruption

Two chromosomal races (2n=17 and 2n=15; XO) of the weta Hemideina thoracica meet at the centre of a volcanic region in North Island, New Zealand. Five independent polymorphic genetic markers showed broadly coinciding, steep frequency clines from north to south across this zone beside the flooded crater, Lake Taupo. Three unlinked nuclear gene markers provide estimates of zone width that are at least twice the width of the chromosomal and mitochondrial clines, with cline centres displaced at least 2.5 km. The different zone widths and centres suggest that this hybrid zone is a semipermeable barrier reducing the introgression of the chromosomal markers more than genic markers. We estimate that this species of weta must have a dispersal rate of at least 100 m per generation using the time since the last Taupo eruption (1850 years ago), which covered an area of about 20 000 km2 with pyroclastic flow.

Analysis of a contact zone in the Forficula auricularia L. (Dermaptera: Forficulidae) species complex in the Pyrenean Mountains

The taxon Forficula auricularia L. (Dermaptera: Forficulidae) is a complex of two sibling species that differ in life history (number of clutches per year and imaginal diapause) and that have diverged at the molecular level. The study of a contact zone in the Pyrenean Mountains, using the PCR-RFLP method on two mitochondrial regions (the 16S rRNA and the Cytochrome Oxidase intergenic region), revealed the coexistence of the sibling species at intermediate altitude (1200 m) whereas at lower and higher altitudes only one species was found. An allozyme study, conducted simultaneously and based on four polymorphic loci (PGI1, AAT1, Est-P1 and Est-P2), showed no sign of nuclear introgression. The apparent lack of hybridization in the field is consistent with a postzygotic barrier observed in the laboratory (a nearly complete failure to produce F(1) hybrids). This contact zone is probably a sympatric zone between two genetically differentiated species.

Robertsonian translocations and B chromosomes in the Wellington tree weta, Hemideina crassidens (Orthoptera: Anostostomatidae)

Two karyotypes within the species Hemideina crassidens are described, 2n = 15 (XO) and 2n = 19 (XO). These two karyotypes have a NF of 28. The 19-karyotype was found exclusively in the southern part of the species range and the 15-karyotype was found in the north. The differences between the two karyotypes are interpreted as arising from two Robertsonian translocations (fission/fusion). Laboratory matings between weta with the two karyotypes produced viable offspring. During meiosis in F1 intraspecific hybrids metacentric and acrocentric autosomes aligned to form two trivalents, confirming homologies predicted by Robertsonian translocations. The subspecies H. c. crassicruris, (confined to Stephens Island) was found to be polymorphic for a metacentric B chromosome. An unusual association of sex and presence of B chromosome was observed in this island population with Bs found only in male weta.

Molecular phylogenetic analysis of the Pneumoroidea (Orthoptera, Caelifera): molecular data resolve morphological character conflicts in the basal acridomorpha

A key transition in the evolution of the insect suborder Caelifera (Orthoptera; Insecta) was from predominantly non-angiosperm-feeding basal lineages to the modern acridomorph fauna (grasshoppers and related insects). However, because of conflicts in the distribution of several complex morphological characters, the relationships of the presumed intermediates, and in particular of the superfamily Pneumoroidea, are presently unclear. We undertook a phylogenetic study of representatives of all of the transitional acridomorph families using mitochondrial and nuclear DNA sequences. No support for pneumoroid monophyly was obtained from nonparametric bootstrap analysis. Furthermore, adopting a maximum-likelihood approach, specific hypotheses of relationships within the Pneumoroidea were firmly rejected using parametric bootstrapping and Kishino-Hasegawa tests. The results indicate that the Pneumoroidea are at best a grade. This distinction implies that the evolution of the proposed pneumoroid synapomorphies, femoro-abdominal stridulation and simple male genital structure, might previously have been misinterpreted as cases of single character gains or losses within lineages. Reconstructions of character states for the femoro-abdominal stridulation indicate that, in fact, multiple losses or gains are equally likely. An important implication of our findings is that, in grasshoppers, auditory tympana may have evolved before stridulation, supporting the argument that the original function of tympana may have been related not to conspecific communication but to predator detection. Overall, the results of this study emphasize the high information content of these minor groups (in this case, the four intermediate families under consideration contain only 0.2% of extant orthopteran species diversity). Our analyses also demonstrate the advantages of model-based methods in analyzing systematic problems and, in particular, of the importance of testing specific phylogenetic hypotheses when a priori support for groupings (e.g., from nonparametric bootstrapping) is marginal.

Phylogeographical pattern correlates with pliocene mountain building in the alpine scree weta (Orthoptera, anostostomatidae)

Most research on the biological effects of Pleistocene glaciation and refugia has been undertaken in the northern hemisphere and focuses on lowland taxa. Using single-strand conformation polymorphism (SSCP) analysis and sequencing of mitochondrial cytochrome oxidase I, we explored the intraspecific phylogeography of a flightless orthopteran (the alpine scree weta, Deinacrida connectens) that is adapted to the alpine zone of South Island, New Zealand. We found that several mountain ranges and regions had their own reciprocally monophyletic, deeply differentiated lineages. Corrected genetic distance among lineages was 8.4% (Kimura 2-parameter [K2P]) / 13% (GTR + I + Gamma), whereas within-lineage distances were only 2.8% (K2P) / 3.2% (GTR + I + Gamma). We propose a model to explain this phylogeographical structure, which links the radiation of D. connectens to Pliocene mountain building, and maintenance of this structure through the combined effects of mountain-top isolation during Pleistocene interglacials and ice barriers to dispersal during glacials.

Satellite DNA variation in parental and derived unisexual hybrids of Bacillus stick insects (Phasmatodea)

The Bag320 sequence family of satellite DNA (satDNA) has been found in some stick insect taxa: the bisexual Bacillus grandii, the related parthenogen B. atticus and their hybrids with B. rossius. However, under the same experimental conditions, the Bag320 sequences were not found in B. rossius. Bag320 sequences of the clonal hybrid B. whitei (= B. rossius/grandii grandii) intermingled with those of B. grandii in all plotted dendrograms. On the whole, satDNA features (restriction pattern, sequence variation, fluorescent in situ hybridization (FISH)), allozymes and karyology support a relatively recent origin of B. whitei. Our investigations on unisexual hybrids of Bacillus also suggested that their origin and clonal reproduction allow the occurrence of different sequence subsets of limited variability in isolated populations stemming from the hybridization focus.

Combined molecular phylogenetic analysis of the Orthoptera (Arthropoda, Insecta) and implications for their higher systematics

A phylogenetic analysis of mitochondrial and nuclear rDNA sequences from species of all the superfamilies of the insect order Orthoptera (grasshoppers, crickets, and relatives) confirmed that although mitochondrial sequences provided good resolution of the youngest superfamilies, nuclear rDNA sequences were necessary to separate the basal groups. To try to reconcile these data sets into a single, fully resolved orthopteran phylogeny, we adopted consensus and combined data strategies. The consensus analysis produced a partially resolved tree that lacked several well-supported features of the individual analyses. However, this lack of resolution was explained by an examination of resampled data sets, which identified the likely source of error as the relatively short length of the individual mitochondrial data partitions. In a subsequent comparison in which the mitochondrial sequences were initially combined, we observed less conflict. We then used two approaches to examine the validity of combining all of the data in a single analysis: comparative analysis of trees recovered from resampled data sets, and the application of a randomization test. Because the results did not point to significant levels of heterogeneity in phylogenetic signal between the mitochondrial and nuclear data sets, we therefore proceeded with a combined analysis. Reconstructing phylogenies under the minimum evolution and maximum likelihood optimality criteria, we examined monophyly of the major orthopteran groups, using nonparametric and parametric bootstrap analysis and Kishino-Hasegawa tests. Our analysis suggests that phylogeny reconstruction under the maximum likelihood criteria is the most discriminating approach for the combined sequences. The results indicate, moreover, that the caeliferan Pneumoroidea and Pamphagoidea, as previously suggested, are polyphyletic. The Acridoidea is redefined to include all pamphagoid families other than the Pyrgomorphidae, which we propose should be accorded superfamily status.

Evolution of the interaction between Hox genes and a downstream target

Segmental identities along the insect body depend on the activities of Hox genes [1,2]. In Drosophila melanogaster, one well-studied Hox regulatory target is Distal-less (Dll), which is required for the development of distal limb structures [3]. In abdominal segments, Dll transcription is prevented when Hox proteins of the Bithorax Complex (BX-C) bind to cis-regulatory elements upstream of the Dll transcription start site [4,5]. Previous evolutionary comparisons of gene expression patterns suggest that this direct repression is conserved between Diptera and Lepidoptera, but is absent in the Crustacea [6,7]. We examined gene expression patterns in three orders of hexapods, all of which develop abdominal appendages, in order to determine when the strong repressive interaction between BX-C proteins and Dll appeared during evolution. In each of the species examined, Dll expression was initiated in abdominal cells despite the presence of high levels of BX-C proteins. It appears that the strong repressive effects of BX-C proteins on Dll expression arose relatively late in insect evolution. We suggest that the regulatory interaction between the BX-C genes and Dll has evolved within the hexapods in a complex, segment-specific manner.

Inferences about orthopteroid phylogeny and molecular evolution from small subunit nuclear ribosomal DNA sequences

We determined DNA sequences of SSU rRNA genes in twenty-nine polyneopteran insect species and aligned these with homologues from eight other insects. In a phylogenetic analysis we recovered the classic divisions of Palaeoptera and Neoptera, with the latter divided into monophyletic Paraneoptera and Polyneoptera. The polyneopterans divided into three lineages: one includes the Grylloblattodea, Dermaptera and Plecoptera, the second contains the Blattodea, and the third (Orthopteroidea sensu Hennig) contains the Embiidina, Phasmida, and Orthoptera, in that order. The monophyly of the Orthoptera is supported by the analyses, as is the separation between taxa from its suborders Caelifera and Ensifera. The Caelifera are not always supported as a monophyletic group; the basal Tridactyloidea are separated from the rest of the Caelifera in some analyses. Inside of Tridactyloidea, the Acridoidea, Pamphagoidea, Pneumoroidea and Trigonopterygoidea are always recovered as a monophyletic group. We also examined the basal orthopteran relationships, with the specific aim of assessing the antiquity of the Ensifera. Character state reconstructions indicated that the ancestral ensiferan sequence is very similar to the ancestral orthopteran sequence. However, likelihood ratio tests rejected the null hypothesis of a molecular clock and we conclude that a change in substitution rate has occurred within the Orthoptera and several of the other polyneopteran orders. Similar observations have been made in holometabolous insects, suggesting that variation in substitution rate is a general feature of insect nuclear rRNA evolution.

Synaptonemal complex analysis of the X1X2Y trivalent in Mantis religiosa L. males: inferences on the origin and maintenance of the sex-determining mechanism

Characterization of sex chromosomes in males of Mantis religiosa L. (2n = 24 + X1X2Y) was carried out by C-banding, silver staining and fluorescence in situ hybridization. They are meta- or submetacentric, their arms being designated as X1L, X1R, X2R, X2L, YL and YR. Meiotic behaviour of the sex trivalent was examined through the analysis of synaptonemal complexes (SCs), prometaphase I (metaphase I) and metaphase II nuclei. On the basis of the SC analysis, chromosomal length measurements at mitosis and prometaphase I and data from several orthopteran species, it is proposed that the breakpoints of the reciprocal translocation that originated this complex sex-determining mechanism were close to the centromeres of the X and the largest autosome, and that the asynapsed X1L and X2R regions observed in the sex trivalent at pachytene represent the original X chromosome. The X centromere being probably that of the X2 element because it lacks a partner in the SC pachytene trivalent. The relationship among synaptic pattern, chiasma localization and balanced segregation of the sex trivalent is also discussed.

The Bag320 satellite DNA family in Bacillus stick insects (Phasmatodea): different rates of molecular evolution of highly repetitive DNA in bisexual and parthenogenic taxa

The Bag320 satellite DNA (satDNA) family was studied in seven populations of the stick insects Bacillus atticus (parthenogenetic, unisexual) and Bacillus grandii (bisexual). It was characterized as widespread in all zymoraces of B. atticus and in all subspecies of B. grandii. The copy number of this satellite is higher in the bisexual B. grandii (15%-20% of the genome) than in the parthenogenetic B. atticus (2%-5% of the genome). The nucleotide sequences of 12 Bag320 clones from B. atticus and 17 from B. grandii differed at 13 characteristic positions by fixed nucleotide substitutions. Thus, nucleotide sequences from both species cluster conspecifically in phylogenetic dendrograms. The nucleotide sequences derived from B. grandii grandii could be clearly discriminated from those of B. grandii benazzii and B. grandii maretimi on the basis of 25 variable sites, although all taxa come from Sicily. In contrast, the Bag320 sequences from B. atticus could not be discriminated accordingly, although they derive from geographically quite distant populations of its three zymoraces (the Italian and Greek B. atticus atticus, the Greek and Turkish B. atticus carius, and the Cyprian B. atticus cyprius). The different rate of evolutionary turnover of the Bag320 satDNA in both species can be related to their different modes of reproduction. This indicates that meiosis and chromosome segregation affect processes in satDNA diversification.