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.     

Geographical variability in the pericentric inversion system of the grasshopper Trimerotropis pseudofasciata

Island and mainland populations of Trimerotropis pseudofasciata from California were compared with respect to the nature and extent of their percentric inversion systems. Island populations generally have more chromosomes polymorphic for centromere position than mainland populations and a considerably higher percentage of the genome in these island populations is in a structurally heterozygous state. Thus, although geographically peripheral, the islands provide habitats capable of supporting denser and more chromosomally polymorphic populations than the mainland. Chiasmata are generally localized to terminal positions in all classes of chromosomes and do not occur in the inverted regions of inversion heterozygotes. Chiasma frequency is highest in inversion homozygotes. It is hypothesized that the inversion system in T. pseudofasciata serves the dual synergistic function of preserving allelic sequences in the inversion region intact through inversion heterozygosity and limiting the generation of variability in regions outside the inversion by increasing terminal chiasmata. Additionally, it is argued that it is the gene sequence on only the inversion chromosome that is important in Trimerotropis. This condition contrasts with the co-adapted pattern seen in Drosophila where the gene sequences on both chromosomes in the inversion heterozygote are simultaneously important.     

Genetic and chromosomal polymorphism in hybridizing populations of the grasshopper Podisma pedestris

The grasshopper Podisma pedistris occurs in two chromosome races, which have XO/XX and neo-XY sex chromosome systems. We have studied chromosomal and electrophoretic variation in populations where these two races meet and hybridize, in an area near the town of Seyne, Alpes Maritimes, southern France. Allozyme variation, at 21 loci in 11 populations, does not seem to show any relationship to the underlying cline in the frequency of the two chromosome types. This indicates that the chromosomal cline does not offer a strong barrier to the flow of genes at other loci. The XO/XX race in this area occurs on a single plateau, isolated from other populations with the same karyotype. It is suggested that this form is only able to persist here because the introgression of neo-XY chromosomes is inhibited by steep cliffs, which tend to keep the two races apart.     

Chromosome studies in Orchidaceae from Argentina

The center of diversity of Argentinean orchids is in the northeast region of the country. Chromosome numbers and karyotype features of 43 species belonging to 28 genera are presented here. Five chromosome records are the first ones at the genus level; these taxa are Aspidogyne kuckzinskii (2n = 42), Eurystyles actinosophila (2n = 56), Skeptrostachys paraguayensis (2n = 46), Stigmatosema polyaden (2n = 40) and Zygostates alleniana (2n = 54). In addition, a chromosome number is presented for the first time for 15 species: Corymborkis flava (2n = 56), Cyclopogon callophyllus (2n = 28), C. oliganthus (2n = 64), Cyrtopodium hatschbachii (2n = 46), C. palmifrons (2n = 46), Galeandra beyrichii (2n = 54), Habenaria bractescens (2n = 44), Oncidium edwallii (2n = 42), O. fimbriatum (2n = 56), O. pubes (2n = 84), O. riograndense (2n = 56), Pelexia ekmanii (2n = 46), P. lindmanii (2n = 46) and Warrea warreana (2n = 48). For Oncidium longicornu (2n = 42), O. divaricatum (2n = 56) and Sarcoglottis fasciculata (2n = 46+1B?, 46+3B?), a new cytotype was found. Chromosome data support phylogenetic relationships proposed by previous cytological, morphologic and molecular analyses, and in all the cases cover some gaps in the South American literature on orchid chromosomes.     

Chromosome numbers of Coleoptera from Argentina

A list is presented containing data on chromosome numbers and sex determining mechanisms of 90 species of Argentina beetles, belonging to the families Staphylinidae (2 spp.), Meloidae (3 spp.), Elateridae (1 sp.), Coccinellidae (5 spp.), Tenebrionidae (11 spp.), Scarabaeidae (30 spp.), Cerambycidae (3 spp.), Chrysomelidae (27 spp.), Curculionidae (7 spp.) and Lampyridae (1 sp.), Asphaera t-album (Chrysomelidae) had n=10+X+6y; in Epicauta atomaria (Meloidae) individuals with 2 n=22, 21 and 20 were found.This work was supported by grants of National Research Council of Argentina (CONICET) and SUBSYT.     

Distribution of a 9.1-kb insertion-deletion polymorphism among native and admixed populations from Argentina

We studied five population samples from Argentina, four drawn from Native American groups of the northeast region (Wichí, Pilagá, Toba, and Mbyá-Guaraní) and one from two small villages of the Córdoba province. In this study we report genotypes and allele frequencies of the 9.1-kb insertion-deletion polymorphism located on chromosome 22. The frequency of the deletion allele ranges from 0.276 in the Mbyá-Guaraní to 0.470 in the Pilagá. The coefficient of population differentiation is fairly low (F(ST) = 0.013), does not reflect any geographic or linguistic pattern, and seems to be more related to stochastic processes than to directional forces.     

Chromosome inversion polymorphism in natural populations of Drosophila punjabiensis Parshad and Paika

Drosophila punjabiensis, a member of the montium subgroup of the melanogaster species group is a very common and widespread species of Drosophila in the Indian subcontinent. Analysis of different geographic populations of this species in India has revealed altogether nine paracentric inversions. The relationship between inversions and the different environmental conditions is discussed. The pattern of inversion polymorphism in D. punjabiensis and its sibling species, D. jambulina are compared.     

Paracentric inversion polymorphism in the grasshopper Boonacris alticola

Paracentric inversion heterozygosity can be detected at pachytene by observation of frequent regions of asynapsis and reinforced by observation of the elimination of a chiasma in the region of the inversion at diplotene and by a low level of bridges and fragments at anaphase. We present evidence that paracentric inversion polymorphism can persist in a grasshopper population despite a low level of crossing over within the inverted region in heterozygotes. Lethality resulting from aneuploidy due to limited crossing over within the region of the inversion appears to be more than compensated for by heterosis.     

Chromosome polymorphism in triploid populations of Fritillaria lanceolata Pursh (Liliaceae) in California

A cytological survey of populations of Fritillaria lanceolata in central California reveals thc existence of karyo-ecotypes. Triploids occupy exposed coastal habitats in contrast to the inland woodland habitats characteristic of the diploids. Allocyclic chromosome banding was observed in diploid and triploid individuals from five distinct populations and complete, banded karyotypes were analyzed and assigned. In contrast to diploids, the triploids exhibited extensive chromosome polymorphism in gross morphology and banding as well as significant interclonal karyotype variability. Evidence was obtained from the banding patterns that triploids have arisen repeatedly by the functioning of unreduced gametes in the diploids.     

Aspergillus section Flavi populations from field maize in Argentina

AIMS: Populations of Aspergillus section Flavi were studied from a commercial field of maize in Río Cuarto, Córdoba, Argentina. METHODS AND RESULTS: The Aspergillus species were isolated from soil, debris and insects during three periods: pre-planting, growing maize and post-harvest. The colony count from non-rhizospheric soil in the pre-planting period was higher than in growing maize and the post-harvest period. Debris samples analysed during all periods showed similar infection percentages for Aspergillus section Flavi. The samples of insects collected during the maize-growing period showed a lower percentage of Aspergillus isolates than the samples from soil and debris. Aflatoxigenic strains were present in lower levels in each component of the agroecosystem studied. All the strains that produced sclerotia were L strains. CONCLUSIONS: In this field agroecosystem, the only strains with a high probability for transfer to the storage agroecosystem were L strains with low toxigenic potential. SIGNIFICANCE AND IMPACT OF THE STUDY: Maize pre-harvest contamination with aflatoxigenic inoculum was not significant.     

Inter-population sex chromosome polymorphism in the grasshopper Podisma pedestris

Populations of the alpine grasshopper Podisma pedestris are either completely XO/XX or else completely neo-XY/neo-XX in character. The neo-XY form is limited in its occurrence to near the extreme southwest edge of the present distribution of the species. Both kinds of population also contain B-chromosomes. These are of two types differing with regard to size, stability and origin. Both types can occur in the same population but have not so far been found in the same individual. The pattern of distribution of the larger, mitotically-stable supernumerary suggests that it might be a remnant X-chromosome which became converted into a B in the initial phase of neo-XY evolution. The smaller, partly unstable supernumerary, on the other hand, may well have originated from a heteromorphic S₁₁ pair also found in some of the populations with small B's. The available evidence points to the neo-XY system having evolved following a secondary movement of the species into the higher ground it now occupies after the climatic amelioration at the end of the last ice age.     

Colour polymorphism in the grasshopper Paulinia acuminata

Paulinia acuminata grasshoppers, which are usually green, are found to become darker when feeding on brown Salvinia under natural conditions. In the laboratory the response is not homochromic but is due to melanin deposition, which may be associated with the unfavourable diet and hyperactivity.

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Zusammenfassung Heuschrecken der Art Paulinia acuminata wurden 1971 zur biologischen Bekämpfung des Wasserunkrauts Salvinia molesta auf dem Karibasee importiert. Unter natürlichen Bedingungen scheinen sich die Heuschrecken der Farbe des Nahrungssubstrates anzupassen. Die häufigeren grünen Insekten finden sich auf grünen Pflanzen, olivgrüne bis braune Insekten auf braunen Pflanzen (Homochromie nach Thomas, 1974).Im Laboratorium änderten grüne Paulinia, welche auf braune Salvinia gesetzt wurden, ihre Farbe in dunkelgrün bis fast schwarz, während dunkle Paulinia auf grünen Salvinia hellgrün wurden. Der Farbumschlag erfolgte auch bei absoluter Dunkelheit und bei blinden Insekten. Er war unbeeinflusst von der Farbe des Hintergrundes und deshalb nicht homochrom.Braune Salvinia hatten nachteilige physiologische Effekte auf Paulinia. Die Farbe grüner Paulinia-Morphen beruht auf einer Pigmentmischung eines blauen Pigments, Mesobiliverdin, und eines gelben Karotinoids, wahrscheinlich ß-Carotin. Offenbar benötigen die Insekten für die Mesobiliverdinsynthese eine Diät grüner Salvinia.Die Melanisierung der Kutikula scheint verantwortlich zu sein für die Farbe dunkler Paulinia. Die Farbe verändert sich nur nach Häutungen, da Melanin während der Härtung und des Dunkelwerdens in die frische Kutikula eingelagert wird. Die Melanisierungsintensität wurde verändert nach mindestens fünftägiger Fütterung auf braunen Salvinia. Wie bei gewissen andern Insekten ist die Melanineinlagerung mit Hyperaktivität verbunden. Auf braunen Salvinia gefütterte Paulinia waren viel aktiver als solche von grünen Pflanzen.

     

Inter-population sex chromosome polymorphism in the grasshopper Podisma pedestris

The montane grasshopper Podisma pedestris exists in Europe in two chromosomally distinct kinds of population. One has an XO/XX sex chromosome mechanism and a diploid chromosome number of 23 male, 24 female. The other has a neo-XY/neo-XX system and a diploid number of 22 in each sex. The development of the neo sex system in this instance has resulted from an X/L₃ fusion which has converted the telocentric X element into a metacentric neo-X. In the neo-XY male this has led to a considerable restriction of chiasma formation in the region proximal to the centromere in the L₃ arm of the neo-X. Since this kind of chromosome change must initially have involved a single individual it could only have succeeded in a small population isolate which underwent rapid expansion immediately following the fusion. Such an origin would have been considerably facilitated by either a modification in sex ratio or else some form of meiotic drive.     

Chromosome polymorphism in the yeast Saccharomyces

The variability of chromosomal band patterns was determined by pulse electrophoresis. The natural strains differed by the quantity and electrophoretic mobility of chromosomal DNA bands. The strains of independent genetic stocks originated from the XII race of Saccharomyces cerevisiae showed less significant difference in band patterns than the strains of different species of the Saccharomyces genus. The progeny of among strains with different karyotypes hybrid showed non-regular segregation of parental bands, the occurrence of new bands and the bands with altered mobility. Reverse crosses of hybrid progeny with strains of Peterhoff genetic stocks of S. cerevisiae led to decrease in chromosomal polymorphism. Homozygotization for ski5 allele and selection for increasing the copy number of killer plasmids was accompanied with repeated splash of polymorphism in 1-2 generations of intratetrad and intrafamily crossed hybrid progeny. Subsequent stabilization of electrophoretic karyotype took place, excluding the mendelian dimorphism of chromosome III, with was a stable trait of the last 6 generations of that progeny.     

Chromosome polymorphism of teosinte

Florida teosinte from Honduras and Guanajuato teosinte have most of their knobs internally located and a common inversion in the short arm of chromosome 8. Teosintes from northern Guatemala, Huixta and Monajil, have all their knobs terminally located and do not have any inversions. Therefore, Florida teosinte from Honduras appears to be phylogenetically closer to Guanajuato teosinte than it is to Guatemalan teosintes.——The presence of B chromosomes and an In 8 in Guanajuato teosinte and Florida teosinte from Honduras may constitute evidence of introgression between maize and teosinte.     

Mitotically unstable B chromosome polymorphism in the grasshopper Dichroplus elongatus

Dichroplus elongatus, a widespread South American phytophagous grasshopper, exhibits polymorphisms for supernumerary chromosomes and segments (SS) in natural populations in Argentina. In this paper we review the available information on B chromosome polymorphism in D. elongatus related to geographic distribution, patterns of chromosome variation and influence on sperm formation. In D. elongatus the different forms of supernumerary variants are not independent. The proportion of B-carrying individuals (B prevalence) is negatively correlated with SS10 and positively with SS6 frequencies. The analysis of population structure considering the different supernumerary variants would suggest that the patterns of chromosome variation can not be explained only by random factors. Geographic distribution was analyzed scoring the prevalence of B chromosomes in 13 natural populations collected in three different biogeographical provinces from Northwest (Las Yungas province) and East (Espinal and Pampeana provinces) of Argentina. The detected heterogeneity may be explained by significant differentiation between Northwest and East regions and among populations within Las Yungas and Pampeana provinces. Correlation analysis suggested that B chromosome prevalence is associated with maximum temperature and with latitude. Additional information about the nature of the patterns of B chromosome variation was obtained comparing them with those obtained at the mitochondrial DNA level. The hierarchical analysis of molecular differentiation revealed discrepancy with respect to chromosome differentiation and also suggested that the pattern of B chromosomes may not be explained by historical factors. We also discussed the probable influence on fertility of carriers considering the production of abnormal sperm formation (macro and microspermatids) in relation to the number of Bs per follicle.     

Chromosome polymorphism in Avena ventricosa

The same karyotype which was described previously in A. ventricosa plants from Oran, Algeria was found in plants from Cyprus and in most of the plants from the Apsheron Peninsula, U.S.S.R. This karyotype, which consists of subterminal chromosomes, was designated C_v¹. In the karyotype of about one-third of the Apsheron plants a single pair of submedian chromosomes replaced a pair of long subterminals. This karyotype was designated C_v². The chromosomes formed 7^II at meiosis in both C_v¹C_v¹and C_v¹C_v²hybrids regardless of geographic origin. A heteromorphic bivalent was apparent in PMCs in the C_v¹C_v²hybrids. A pericentric inversion was postulated as the origin of the submedian pair, the C_v²C_v²karyotype being the inversion homozygote. The absence of duplication-deficiency gametes was inferred from the good fertility of the heterozygote. Members of the heteromorphic pair were transmitted in equal proportion and the segregates C_v¹C_v¹, C_v¹C_v²and C_v²C_v²were equally fertile; thus the inversion did not handicap reproduction. The small contemporary colonies of A. ventricosa, with peripheral locations and vast distances between them, because of the full homology and interfertility, are considered remnants of a formerly large central population.Contribution No 282 from the Research Station, Central Experimental Farm, Ottawa, Ontario.This paper is dedicated to the memory of Dr. Barna Györffy, whose untimely death on August 5, 1970 ended a distinguished career that was an example of integrity and scholarship to a troubled generation of Hungarian geneticists.