Meiotic studies in Lygaeus alboornatus Blanchard 1852 (Heteroptera, Lygaeidae, Lygaeinae)

The subfamily Lygaeinae comprises 58 genera with about 500 species distributed world-wide. Despite the great biodiversity of the taxon, cytogenetic data of the group is scarce. To date, only 26 species belonging to 12 genera have been cytogenetically described. As it is the rule for the order Heteroptera, all the species possess holokinetic chromosomes, and a pre-reductional type of meiosis, namely at anaphase I the autosomal bivalents divide reductionally while the sex chromosomes are achiasmatic and divide equationally. Available data reveal that all the Lygaeinae are characterised by a modal diploid number of 14 and an XY/XX sex chromosome determining system. In the present study the male meiotic development of Lygaeus alboornatus from Argentina is analysed. The results demonstrate that the species, though sharing the basic chromosomal features from Lygaeinae, has a diploid number of 12 (10+XY), being this chromosome number the lowest reported so far for the subfamily.Facultad de Ciencias Naturales y Muse

Meiotic studies in Lygaeus alboornatus Blanchard 1852 (Heteroptera, Lygaeidae, Lygaeinae)

The subfamily Lygaeinae comprises 58 genera with about 500 species distributed world-wide. Despite the great biodiversity of the taxon, cytogenetic data of the group is scarce. To date, only 26 species belonging to 12 genera have been cytogenetically described. As it is the rule for the order Heteroptera, all the species possess holokinetic chromosomes, and a pre-reductional type of meiosis, namely at anaphase I the autosomal bivalents divide reductionally while the sex chromosomes are achiasmatic and divide equationally. Available data reveal that all the Lygaeinae are characterised by a modal diploid number of 14 and an XY/XX sex chromosome determining system. In the present study the male meiotic development of Lygaeus alboornatus from Argentina is analysed. The results demonstrate that the species, though sharing the basic chromosomal features from Lygaeinae, has a diploid number of 12 (10+XY), being this chromosome number the lowest reported so far for the subfamily.Facultad de Ciencias Naturales y Muse

Estudos de toxidez de alumínio em genótipos de soja e milho cultivados em bioensaios,

A soja (Glycine max) e o milho (Zea mayz) são culturas importantes para o desenvolvimento sócio-econômico do Rio Grande do Sul. Um fator que pode afetar a produtividade destas culturas é a presença de alumínio em níveis tóxicos que ocorre, principalmente, em solos ácidos. A utilização de genótipos adaptados é uma estratégia para o manejo integrado dos cultivos em solos ácidos. O presente estudo teve como objetivo determinar as concentrações de cálcio e aluminio adequadas a realização de bioensaios para a classificação de genótipos de soja e milho quanto a tolerância à toxidez de aluminio. Foram utilizados três genótipos de soja (6001, 8100 e AL 72.) e dois genótipos de milho (P3081 e TRAKTOR). Os genótipos foram cultivados, pela técnica de bioensaios, em diferentes concentrações de cálcio e alumínio. A concentração de 2,5 mmol dm-3 de cálcio foi adequada para a realização de estudos em bíoensaios nos genótipos de soja e milho, não promovendo restrições no crescimento da raiz principal. A concentração de 0,005 mmol dm-3 de alumínio para soja e 0,025 mmol dm-3 de alumínío para milho, combínadas com 2,5 mmol dm-3 de cálcio permitem diferenciar os genótipos de soja e milho em uma escala de tolerância ao alumini

Behaviour of ring bivalents in holokinetic systems : Alternative sites of spindle attachment in Pachylis argentinus and Nezara viridula (Heteroptera)

Heteropteran chromosomes are holokinetic; during mitosis, sister chromatids segregate parallel to each other but, during meiosis, kinetic activity is restricted to one pair of telomeric regions. This meiotic behaviour has been corroborated for all rod bivalents. For ring bivalents, we have previously proposed that one of the two chiasmata releases first, and a telokinetic activity is also achieved. In the present work we analyse the meiotic behaviour of ring bivalents in Pachylis argentinus (Coreidae) and Nezara viridula (Pentatomidae) and we describe for the first time the chromosome complement and male meiosis of the former (2n=12+2m+X0, pre-reduction of the X). Both species possess a large chromosome pair with a secondary constriction which is a nucleolus organizer region as revealed by in-situ hybridization. Here we propose a new mode of segregation for ring bivalents: when the chromosome pair bears a secondary constriction, it is not essential that one of the chiasmata releases first since these regions or repetitive DNA sequences adjacent to them become functional as alternative sites for microtubule attachment and they undertake chromosome segregation to the poles during anaphase I.Facultad de Ciencias Naturales y Muse

Meiotic studies in Lygaeus alboornatus Blanchard 1852 (Heteroptera, Lygaeidae, Lygaeinae)

The subfamily Lygaeinae comprises 58 genera with about 500 species distributed world-wide. Despite the great biodiversity of the taxon, cytogenetic data of the group is scarce. To date, only 26 species belonging to 12 genera have been cytogenetically described. As it is the rule for the order Heteroptera, all the species possess holokinetic chromosomes, and a pre-reductional type of meiosis, namely at anaphase I the autosomal bivalents divide reductionally while the sex chromosomes are achiasmatic and divide equationally. Available data reveal that all the Lygaeinae are characterised by a modal diploid number of 14 and an XY/XX sex chromosome determining system. In the present study the male meiotic development of Lygaeus alboornatus from Argentina is analysed. The results demonstrate that the species, though sharing the basic chromosomal features from Lygaeinae, has a diploid number of 12 (10+XY), being this chromosome number the lowest reported so far for the subfamily.Facultad de Ciencias Naturales y Muse

Meiotic studies in Lygaeus alboornatus Blanchard 1852 (Heteroptera, Lygaeidae: Lygaeinae)

Fil: Bressa, María José. Facultad de Ciencias Naturales y Museo, Universidad Nacional de La PlataFil: Papeschi, Alba G.. Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Buenos AiresFil: Larramendy, Marcelo Luis. Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plat

Heterochromatin characterization and ribosomal gene location in two monotypic genera of bloodsucker bugs (Cimicidae, Heteroptera) with holokinetic chromosomes and achiasmatic male meiosis

Abstract Members of the family Cimicidae (Heteroptera: Cimicomorpha) are temporary bloodsuckers on birds and bats as primary hosts and humans as secondary hosts. Acanthocrios furnarii (2n = 12 = 10 + XY, male) and Psitticimex uritui (2n = 31 = 28 + X 1 X 2 Y, male) are two monotypic genera of the subfamily Haematosiphoninae, which have achiasmatic male meiosis of collochore type. Here, we examined chromatin organization and constitution of cimicid holokinetic chromosomes by determining the amount, composition and distribution of constitutive heterochromatin, and number and location of nucleolus organizer regions (NORs) in both species. Results showed that these two bloodsucker bugs possess high heterochromatin content and have an achiasmatic male meiosis, in which three regions can be differentiated in each autosomal bivalent: (i) terminal heterochromatic regions in repulsion; (ii) a central region, where the homologous chromosomes are located parallel but without contact between them; and (iii) small areas within the central region, where collochores are detected. Acanthocrios furnarii presented a single NOR on an autosomal pair, whereas P. uritui presented two NORs, one on an autosomal pair and the other on a sex chromosome. All NORs were found to be associated with CMA 3 bright bands, indicating that the whole rDNA repeating unit is rich in G + C base pairs. Based on the variations in the diploid autosomal number, the presence of simple and multiple sex chromosome systems, and the number and location of 18S rDNA loci in the two Cimicidae species studied, we might infer that rDNA clusters and genome are highly dynamic among the representatives of this family

Meiotic studies in Dysdercus Guerin Meneville 1831 (Heteroptera: Pyrrhocoridae) : I. Neo-XY in Dysdercus albofasciatus Berg 1878, a new sex chromosome determining system in Heteroptera

The genus Dysdercus Guerin Meneville 1831 represents the only taxon within the family Pyrrhocoridae in the New World. Based on morphological features, it has been suggested that American species derived from immigrants from the Old World, most probably from the Ethiopian Region. So far, 10 species from Dysdercus, including six species from the Old World and four species from the Neotropical Region have been cytogenetically analyzed. As is characteristic of Heteroptera, they possess holokinetic chromosomes and a prereductional type of meiosis. While the X1X20 sex chromosome system has been reported in all cytologically analyzed species of Dysdercus from the Old World, the system X0 has been found in all but one species from the New World, regardless of the number of autosomes in the complement. In the present study the male meiosis of D. Albofasciatus Berg 1878 was studied in specimens from four different populations from Argentina. The diploid chromosome number was found to be 2n = 10 + neo-XY. The neo-X shows at each subterminal region a positively heteropycnotic and DAPI-bright segment which corresponds to the ancestral X-chromosome. The origin of this neo-XY system involved, most probably, a subterminal insertion of the ancestral X chromosome in an autosome, followed by a large inversion, which included part of the original X chromosome.Facultad de Ciencias Naturales y Muse

Meiotic studies in Dysdercus Guerin Meneville 1831 (Heteroptera: Pyrrhocoridae) : I. Neo-XY in Dysdercus albofasciatus Berg 1878, a new sex chromosome determining system in Heteroptera

The genus Dysdercus Guerin Meneville 1831 represents the only taxon within the family Pyrrhocoridae in the New World. Based on morphological features, it has been suggested that American species derived from immigrants from the Old World, most probably from the Ethiopian Region. So far, 10 species from Dysdercus, including six species from the Old World and four species from the Neotropical Region have been cytogenetically analyzed. As is characteristic of Heteroptera, they possess holokinetic chromosomes and a prereductional type of meiosis. While the X1X20 sex chromosome system has been reported in all cytologically analyzed species of Dysdercus from the Old World, the system X0 has been found in all but one species from the New World, regardless of the number of autosomes in the complement. In the present study the male meiosis of D. Albofasciatus Berg 1878 was studied in specimens from four different populations from Argentina. The diploid chromosome number was found to be 2n = 10 + neo-XY. The neo-X shows at each subterminal region a positively heteropycnotic and DAPI-bright segment which corresponds to the ancestral X-chromosome. The origin of this neo-XY system involved, most probably, a subterminal insertion of the ancestral X chromosome in an autosome, followed by a large inversion, which included part of the original X chromosome.Facultad de Ciencias Naturales y Muse

Meiotic studies in Largus rufipennis (Castelnau) (Largidae, Heteroptera). II: reciprocal translocation heterozygosity

Specimens of Largus rufipennis (Castelnau) (Largidae, Heteroptera) from three different populations from Argentina (Itaembe, Misiones Province; Tornquist and Ciudad Universitaria, Buenos Aires Province) were cytogenetically studied. Meiotic characteristics of these populations are compared with previous reports on the species. In the population from Itaembe, heterozygosity for a reciprocal translocation was encountered; this finding is the first report for this type of chromosome rearrangement in the order Heteroptera. The role of reciprocal translocations in karyotype evolution in organisms with holokinetic chromosomes is analyzed and discussed.Facultad de Ciencias Naturales y Muse