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

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

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

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

Cytogenetic analysis of three species of Pseudacteon (Diptera, Phoridae) parasitoids of the fire ants using standard and molecular techniques

Pseudacteon flies, parasitoids of worker ants, are being intensively studied as potentially effective agents in the biological control of the invasive pest fire ant genus Solenopsis (Hymenoptera: Formicidae). This is the first attempt to describe the karyotype of P. curvatus Borgmeier, P. nocens Borgmeier and P. tricuspis Borgmeier. The three species possess 2n = 6; chromosomes I and II were metacentric in the three species, but chromosome pair III was subtelocentric in P. curvatus and P. tricuspis, and telocentric in P. nocens. All three species possess a C positive band in chromosome II, lack C positive heterochromatin on chromosome I, and are mostly differentiated with respect to chromosome III. P. curvatus and P. tricuspis possess a C positive band, but at different locations, whereas this band is absent in P. nocens. Heterochromatic bands are neither AT nor GC rich as revealed by fluorescent banding. In situ hybridization with an 18S rDNA probe revealed a signal on chromosome II in a similar location to the C positive band in the three species. The apparent lack of morphologically distinct sex chromosomes is consistent with proposals of environmental sex determination in the genus. Small differences detected in chromosome length and morphology suggests that chromosomes have been highly conserved during the evolutionary radiation of Pseudacteon. Possible mechanisms of karyotype evolution in the three species are suggested

Meiotic Studies in Largus-Rufipennis (Castelnau) (Largidae, Heteroptera) - II - Reciprocal Translocation Heterozygosity

Fil: Bressa, María José. Cátedra de Citología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Papeschi, Alba G.. Genetica. Departamento de Ciencias Biológicas. Universidad de Buenos Aires; ArgentinaFil: Mola, Liliana. Genetica. Departamento de Ciencias Biológicas. Universidad de Buenos Aires; ArgentinaFil: Larramendy, Marcelo Luis. Cátedra de Citología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Heterochromatin variation in Artemia populations

The genus Artemia is an interesting model organism for evolutionary studies since many factors driving speciation have been observed in the genus. It has been suggested that in this genus heterochromatin content could be a reliable criteria to establish taxonomic identity of populations. In the present work the heterochromatin content was determined in 4 populations of A. franciscana and seven populations of A. persimilis, six from Argentina and one from Chile. Heterochromatin was revealed by C-banding and the heterochromatin content (measured as chromocenter number and C-positive area in nauplii interphase nuclei) was compared. A standardized procedure to evaluate the heterochromatin content is here proposed so that the results from different laboratories could be compared. We analyze the intra and interspecific variation in heterochromatin content in the different Artemia populations and we discuss the value of this trait as a population and/or specific cytogenetic marker.Peer Reviewe