Chiasma localization and incomplete synapsis in two species of Tetrigidae (Orthoptera).
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Chromosomal polymorphism, morphometric traits and mating success in Leptysma argentina Bruner (Orthoptera).
The South-American species Leptysma argentina Bruner is polymorphic for a centric fusion between chromosomal pairs 3 and 6 (fusion 3/6). Cytogenetic and morphological studies revealed that fusion 3/6 significantly increases some morphometric variables in males. A selection components study showed that the fusion is positively selected for longevity, the direct effect being exerted on thorax height. Moreover, a unisexual approach revealed that sexual male selection acts by increasing third femur length. In the present study the effect of fusion 3/6 on morphometric variables and the effect of body size and karyotype on mating success in both males and females were analysed through a bisexual approach. Total body length (TL) and third femur length (FL) were significantly larger amongst the fusion carrier females. Besides, the largest females and the carriers of the fusion have increased mating success. The selection differential suggests that directional sexual selection favours the females with increased TL and fusion dosage; however, the selection gradient revealed that none of the variables here analysed is a direct target of sexual selection. The male sexual selection study agrees with previous results, showing the importance of the third pair of legs in male mating success among grasshoppers.
Animals↗
Pitch discrimination in Orthoptera (Insecta) demonstrated by responses of central auditory neurones.
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Inversion polymorphisms in Trimerotropis pallidipennis (Orthoptera): clinical variation along an altitudinal gradient.
Six populations of Trimerotropis pallidipennis located along an altitudinal gradient in the Antinaco-Los Colorados valley (La Rioja, Argentina), were cytologically analysed. The male karyotype consists of 23 chromosomes (22 + XO) with three long pairs submetacentric, the X-chromosome metacentric and the remaining ones basically acrocentric. Populations from La Rioja were polymorphic for seven pericentric inversions. Correlations between chromosome frequencies and altitude were statistically tested. In most cases, variables were either positively or negatively related in a significant fashion. As a consequence, mean populational heterozygosis (measured as the mean number of heteromorphic bivalents per individual per population) was also positively correlated with altitude. These results suggest that altitude (or other correlated environmental variable) may exert a differential selective pressure on coadapted gene blocks in the mutually inverted sequences. The possible relation of these results with the central-marginal model is discussed.
Altitude↗
Are solitary and gregarious Mormon crickets (Anabrus simplex, Orthoptera, Tettigoniidae) genetically distinct?
Phase polyphenisms are usually thought to reflect plastic responses of species, independent of genetic differences; however, phase differences could correlate with genetic differentiation for various reasons. Mormon crickets appear to occur in two phases that differ in morphology and behaviour. Solitary individuals are cryptic and sedentary whereas gregarious individuals form bands, migrate, and are aposematically coloured. These traits have been thought to be phenotypically plastic and induced by environmental conditions. However, there has been no previous investigation of the extent of genetic differences between solitary and gregarious populations of this widespread North American species. We sequenced two mitochondrial genes, COII and COIII, in samples of Mormon crickets from gregarious populations west of the continental divide and solitary mountain populations primarily east of the divide. Sequencing revealed two genetically distinct clades that broadly correspond with the solitary eastern populations and the mainly gregarious western populations. We used coalescent modelling to test the hypothesis that the species consists of two deep genetic clades, as opposed to a series of equally distinct populations. Results allowed us to reject the null hypothesis that a radiation independent of phase produced these clades, and molecular clock estimates indicate the time of divergence to be approximately 2 million years ago. This work establishes that the solitary populations found in the mountains on the eastern slope are part of a clade that is genetically distinct from the western populations, which are primarily gregarious, and the implications of this apparent correlation between phase and genetic differentiation are discussed.
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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.
Adaptation, Physiological↗
[SUPPLEMENTARY DESCRIPTION OF GREGARINA DAVINI LEGER AND DUBOSCQ 1899 (EUGREGARINA, GREGARINIDAE), A PARASITE OF GRYLLOMO RPHA DALMATINA OCSK (ORTHOPTERA, GRYLLOIDEA)].
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Electron microscope studies on the cells of the malpighian tubules of the grasshopper (Orthoptera, Acrididae).
For purposes of description, the cells of the Malpighian tubules of the grasshopper may be divided into basal, intermediate, and apical zones. The basal zone of the cell contains what appears to be an elaborate infolding of the cell membrane at the base. This condition results in the basal cell cytoplasm being divided into many compartments. The compartments contain mitochondria that are often arranged in rows. Other small bodies which possess relatively dense outer borders and less dense cores were observed within the compartments. These bodies are unidentified. The brush border of the apical zone contains a multitude of vertically arranged protoplasmic processes. Stages were found which suggest that the filamentous mitochondria migrate from the cell body to the base of the protoplasmic processes, where they enter them and move apically. Some of the mitochondria were observed at the very tips of the processes where they enlarge producing an accompanying bulging of the tips. This condition is interpreted as a stage in the pinching off of the mitochondria-laden tips of the protoplasmic processes.
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A cytological survey of wild populations of Trimerotropis and circotettix (Orthoptera, Acrididae). II. Racial differentiation in T. Sparsa.
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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.
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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.
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Inversion polymorphisms and natural selection in Trimerotropis pallidipennis (Orthoptera).
Grasshoppers have been much less studied than Drosophila when it comes to inversion polymorphisms, despite the occurrence of this rearrangement in several species of grasshoppers. In the present study, 354 males from a natural population of the New World species Trimerotropis pallidipennis, polymorphic for 6 pericentric inversions in 4 chromosome pairs, were sampled at the beginning and at the end of the adult life span. This sampling, along with the fact that generations in this grasshopper are annual and discrete, was done to detect differential adult male longevity among karyotypes and departures from formal null models, such as gametic phase equilibrium. These methods allow the detection of natural selection taking place in the wild. The comparison between age classes showed that some inversions were significantly more frequent in one sample, thus revealing the operation of natural selection. Gametic phase disequilibrium was detected in the sample of aged males but not in the sample of young ones. Furthermore, here we aim to detect the phenotypic targets of longevity selection by examining morphometric characters, in order to have a clearer idea of the relation between inversions and natural selection in this species. These results corroborate previous studies that suggested that the inversions are involved in natural selection, and an adaptive model has been proposed for the pattern of inversion frequencies throughout several populations at different altitudes and latitudes.
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Telomeric and interstitial telomeric-like DNA sequences in Orthoptera genomes.
A (TTAGG)n-specific telomeric DNA probe was hybridized to 11 orthopteroid insect genomes by fluorescence in situ hybridization. Nine different genera, mainly distributed within two evolutionary branches with male chromosome numbers 2n = 23 and 2n = 17 were included in the analysis. Telomere sequences yielded positive signals in every telomere and there was a considerable number of interstitial telomeric-like sequences, mainly located at the distal end of some, but not all, subterminal chromosome regions. One of the species, Pyrgomorpha conica, showed massive hybridization signals associated with constitutive heterochromatin. The results are discussed along two lines: (i) the chromosomal evolutionary trends within this group of insects and (ii) the putative role that ITs may play in a genome when they are considered telomere-derived, but not telomere-functional, DNA sequences.
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Behavioral fever and therapy in a rickettsia-infected Orthoptera.
Gryllus bimaculatus were infected with an intracellular prokaryote, Rickettsiella grylli, then reared either at fixed temperatures or in a temperature gradient (22-36 degrees C) where they could select the temperature they preferred. Only 50% of the infected insects reared at 28 degrees C or less survived after 20 days, against 75% of those reared at 30 degrees C or more and 90% of those in the temperature gradient. Examination of smears of insect tissue showed that all (100%) of the infected insects reared between 23 and 29 degrees C had developed a strong rickettsial infection. Only 20% of the insects reared in a gradient of temperature showed signs of strong infection. Body temperature of crickets in the temperature gradient, recorded using thin thermocouples, was 33 degrees C in infected crickets and 26.6 degrees C in controls. It is concluded that thermoregulatory behavior was used by the insects to produce a fever when infected with Rickettsiella grylli. This protected them and increased survival capacity.
Animal Husbandry↗
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.
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Molecular cytogenetic characterization and chromosomal distribution of the satellite DNA in the genome of Oxya hyla intricata (Orthoptera: Catantopidae).
The genomic DNA of the grasshopper (Oxya hyla intricata) was subjected to electrophoresis after digestion with HaeIII, and the result showed two bands of highly repetitive DNA, approximately 200 and 400 bp in length. The 200-bp HaeIII-digested fragment was cloned and characterized by sequencing and fluorescence in situ hybridization (FISH). The results showed the presence of two distinct satellite DNA (stDNA) families: one consisting of a 169-bp repeated element having an A+T content of 60.9% and the other consisting of a 204-bp repeated element having an A+T content of 53.9%. No significant homology between the two stDNA families was observed. FISH showed that the chromosomal locations of these families are different from each other. The 169-bp element was located in the C-band-positive regions of the short arms of most of the chromosomes, whereas the 204-bp element was located in the centromeric regions of three chromosome pairs. These results imply that the origins of these two DNA families are different. The results of zoo-blot hybridization to the genomic DNA from four Oxya species, O. hyla intricata, O. japonica japonica, O. chinensis formosana, and O. yezoensis, suggest that the two stDNA families found in the present study are species-specific for O. hyla intricata.
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Localization of the circadian pacemakers of Hemideina thoracica (Orthoptera; Stenopelmatidae).
The location of the circadian pacemakers of the orthopteran Hemideina thoracica (White) has been investigated through observation of the effects of surgical removal of brain tissues (principally optic lobes and tracts) on free-running and entrained locomotor rhythms. Bilobectomy and severance of optic tracts invariably resulted in arrhythmicity, whereas rhythmicity was sustained following unilateral lobectomy, generally with increases in the free-running period (FRP) and decreases in both the active-phase lengths and activity-to-rest ratios of the rhythm. Bilobectomized subjects could be entrained by temperature cycles, but exhibited no transients or residual rhythmicity, indicating that temperature brought about a direct response or masking effect. These results support the hypothesis that the circadian locomotor pacemakers of Hemideina are located within each optic lobe, and that there are no extraoptic centers for the control of the timing of locomotor activity. Although confirmation of the pacemaker role of the optic lobes requires transplantation of the tissues, the conclusion may be drawn by inference from other studies (e.g., Leucophaea maderae--Page, 1983; Gryllus bimaculatus--Tomioka and Chiba, 1986). Light entrainment continued after surgical binding and blackening of the compound eyes and ocelli, supporting the view that direct illumination of neural tissue through the cuticle may be one possible pathway for light entrainment.
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Control systems models for the circadian clock of the New Zealand weta, Hemideina thoracica (Orthoptera: Stenopelmatidae)
The New Zealand weta, Hemideina thoracica, is a nocturnal orthopteran insect which emerges from holes in trees or from under bark soon after sunset to forage for several hours on plant and animal material before returning to its refuge before dawn. In tests of the internal clock hypothesis it exhibits clear circadian locomotor rhythms in which the period is initially somewhat less than 24 h, but frequently spontaneously increases to over 25 h. The rhythms are entrainable by light and temperature cycles, obey Aschoff's Law and are temperature compensated. A single oscillator feedback model accounts for these basic properties of the weta clock, but does not explain a variety of examples of rhythm lability, such as day skipping, spontaneous change in period, scalloping and desynchrony typically found in the real data. To account for these characteristics the model is expanded into two linked populations of oscillators, which retain the basic properties of the simple model and in addition interact through their coupling to show the various types of free-run lability. To make these control systems models compatible with the molecular interpretation of circadian biology, each of the components in the feedback loop is matched with molecular function and structure.
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