Liliana M. Mola

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.

CYTOGENETIC HETEROGENEITY IN COMMON HAPLOGYNE SPIDERS FROM ARGENTINA (ARACHNIDA, ARANEAE)

Abstract The spermatogenesis of four species of haplogyne spiders from Argentina is analyzed. Dysdera crocota (Dysderidae) (n = 5 + X0) has holokinetic chromosomes, achiasmatic male meiosis and a post-reductional division of the sex chromosome. Ariadna boesenbergii (Segestriidae) (n = 4 + X0) also possesses holokinetic chromosomes, but meiosis is chiasmatic and the X chromosome divides pre-reductionally. Kukulcania hibernalis (Filistatidae) (n = 11 + X1X20) and Scytodes globula (Scytodidae) (n = 6 + X0) have metacentric and submetacentric chromosomes, chiasmatic meiosis and the sex chromosomes divide pre-reductionally. Kukulcania hibernalis possesses a bimodal karyotype and a particular chromatin coiling during prophase I, while Scytodes globula has striking proximal localization of chiasmata. These results show that Haplogynae present high cytogenetic heterogeneity: species with holokinetic chromosomes as well as species with monocentric chromosomes (metacentric and submetacentric), and species with low diploid numbers, achiasmatic meiosis and proximal chiasma localization.

CYTOGENETICS IN THREE SPECIES OF POLYBETES SIMON 1897 FROM ARGENTINA (ARANEAE, SPARASSIDAE) I. KARYOTYPE AND CHROMOSOME BANDING PATTERN

Abstract Species of Polybetes are known exclusively from South America. Currently there are 13 described species, 9 occurring in Argentina. Cytogenetic studies in spiders are scarce; the cytogenetics of only about 1% of nearly 39,500 described species are known. Within the Sparassidae, 38 species out of 1,009 (< 4%) have been cytogenetically analyzed; the most frequent chromosome number is 2n = 43/46 (male/female), n = 20 + X1X2X3, present in almost half of the species studied. Female diploid chromosome number is only known for four species: Heteropoda venatoria (Linnaeus 1767) (2n = 44); Pediana regina (L. Koch 1875), Isopeda sp. and Olios sp. (2n = 46). Within the genus Polybetes, only P. pythagoricus (Holmberg 1875) had been previuosly cytogenetically analyzed. In the present work, the karyotype, heterochromatin content and distribution, and silver stained nucleolus-organizer regions of P. pythagoricus, P. rapidus (Keyserling 1880) and P. punctulatus Mello-Leitão 1944 are described and compared. In P. pythagoricus the identification of the chromosome pairs by means of G-banding is also performed. Females of the three species show a chromosome complement of 44 telocentric chromosomes, with a similar karyotype. Males of P. pythagoricus show 42 telocentric chromosomes, the two sex chromosomes being the largest and of different size. In the three species, two pairs of telomeric NORs and small pericentromeric positive C-bands in all chromosomes were detected. This C-banding pattern seems to be characteristic of spiders. Comparative analysis of chromosome complements in Sparassidae indicates that 2n = 42/44 (X1X20/X1X1X2X2) (male/female) may represent the ancestral karyotype for Polybetes.

Intra and Interspecific Karyotype Variability in Five Species of Libellulidae (Anisoptera, Odonata)

SUMMARYChromosome studies were performed on five species of Libellulidae sampled from various Argentine localities. Pantala flavescens (Fabricius), Erythemis attala Selys and Micrathyria hypodydima Calvert have n = 12 + X and present m chromosomes. Brachymesia furcata Hagen also has n = 12 + X, but without m chromosomes and the presence of a clearly heteromorphic autosomal bivalent was a constant feature in all individuals. Micrathyria longifasciata Calvert has n—12, with a neo-XY sex determining system and it presents a larger autosomal bivalent. Comparison of the results obtained for P. flavescens, E. attala, M. hypodydima and B. furcata with studies performed by other authors on non-Argentinian populations showed karyotype differences as well as interspecific differences in the genus Micrathyria.

Sex-Linked Chromosome Heterozygosity in Males of Tityus confluens (Buthidae): A Clue about the Presence of Sex Chromosomes in Scorpions.

Scorpions of the genus Tityus show holokinetic chromosomes, achiasmatic male meiosis and an absence of heteromorphic sex chromosomes, like all Buthidae. In this work, we analysed the meiotic behaviour and chromosome rearrangements of a population of the scorpion Tityus confluens, characterising the cytotypes of males, females and embryos with different cytogenetic techniques. This revealed that all the females were structural homozygotes, while all the males were structural heterozygotes for different chromosome rearrangements. Four different cytotypes were described in males, which differed in chromosome number (2n = 5 and 2n = 6) and meiotic multivalent configurations (chains of four, five and six chromosomes). Based on a detailed mitotic and meiotic analysis, we propose a sequence of chromosome rearrangements that could give rise to each cytotype and in which fusions have played a major role. Based on the comparison of males, females and a brood of embryos, we also propose that the presence of multivalents in males and homologous pairs in females could be associated with the presence of cryptic sex chromosomes, with the male being the heterogametic sex. We propose that the ancestral karyotype of this species could have had homomorphic XY/XX (male/female) sex chromosomes and a fusion could have occurred between the Y chromosome and an autosome.

Cytogenetics of three species of scorpions of the genus Brachistosternus from Argentina (Scorpiones: Bothriuridae)

Abstract Meiotic studies on three phylogenetically distant species of the genus Brachistosternus Pocock from Argentina were conducted. One species is from the subgenus Ministernus Francke 1985, B. ferrugineus Thorell 1876, and two species are from the subgenus Brachistosternus Pocock 1893, B. montanus Roig-Alsina 1977 (Andean species group), and morphologically different populations of B. pentheri Mello-Leitão 1931 (plains species group). All species showed achiasmatic meiosis, absence of heteromorphic bivalents, and bibrachial and monobrachial chromosomes of different sizes. Males of Brachistosternus ferrugineus, B. montanus, and one population of B. pentheri have 2n  =  46. Males of the typical populations of B. pentheri have 2n  =  42. These results suggest that B. pentheri may comprise two species.

Multiple approaches to understanding the taxonomic status of an enigmatic new scorpion species of the genus Tityus (Buthidae) from the biogeographic island of Paraje Tres Cerros (Argentina)

Tityus curupi n. sp., belonging to the bolivianus complex, is described from the biogeographically distinct area of Paraje Tres Cerros in north-eastern Argentina. We also present a molecular species delimitation analysis between Tityus curupi n. sp. and its sister species Tityus uruguayensis Borelli 1901 to confirm species integrity. Furthermore, a cytogenetic analysis is presented for these two species which contain different multivalent associations in meiosis, as a consequence of chromosome rearrangements, and the highest chromosome numbers in the genus.

Meiotic studies in Brachistosternus alienus (Scorpiones; Bothriuridae)

Abstract Brachistosternus Pocock 1893 is the most diverse genus of the scorpion family Bothriuridae. Only four species of the genus have been cytogenetically analyzed so far. We report herein the cytogenetic analysis of Brachistosternus alienus Lönnberg 1898 from Comallo (Río Negro province, Argentina). This species is widely distributed in the Monte phytogeographic province, located in central and northern Argentine Patagonia. Meiotic cells of B. alienus from Comallo show 23 homomorphic achiasmatic bivalents. The karyotype of this species contains scarce AT-rich regions that may be associated with the heterochromatin of centromeric regions. Giacomozzi (1977) reports n  =  14 for B. alienus from Chubut province. Unfortunately, it is not presently possible to determine if those specimens correspond to B. alienus or to a sympatric species, Brachistosternus angustimanus Ojanguren-Affilastro & Roig-Alsina 2001. These different chromosome numbers of the two populations analyzed may reflect the occurrence of a chromosomal polytypism in B. alienus, or they may characterize different species.