On the Origin of Neo-Sex Chromosomes in the Neotropical Dragonflies Rhionaeschna bonariensis and R. planaltica (Aeshnidae, Odonata).

Odonata have holokinetic chromosomes. About 95% of species have an XX/X0 sex chromosome system, with heterogametic males. There are species with neo-XX/neo-XY sex chromosomes resulting from an X chromosome/autosome fusion. The genus Rhionaeschna includes 42 species found in the Americas. We analyzed the distribution of the nucleolar organizer region (NOR) using FISH with rDNA probes in Rhionaeschna bonariensis (n = 12 + neo-XY), R. planaltica (n = 7 + neo-XY), and Aeshna cyanea (n = 13 + X0). In R. bonariensis and A. cyanea, the NOR is located on a large pair of autosomes, which have a secondary constriction in the latter species. In R. planaltica, the NOR is located on the ancestral part of the neo-X chromosome. Meiotic analysis and FISH results in R. planaltica led to the conclusion that the neo-XY system arose by insertion of the ancestral X chromosome into an autosome. Genomic in situ hybridization, performed for the first time in Odonata, highlighted the entire neo-Y chromosome in meiosis of R. bonariensis, suggesting that it consists mainly of repetitive DNA. This feature and the terminal chiasma localization suggest an ancient origin of the neo-XY system. Our study provides new information on the origin and evolution of neo-sex chromosomes in Odonata, including new types of chromosomal rearrangements, NOR transposition, and heterochromatin accumulation.

High karyotypic variation in Orthemis Hagen, 1861 species, with insights about the neo-XY in Orthemisambinigra Calvert, 1909 (Libellulidae, Odonata).

The American dragonfly genus Orthemis Hagen, 1861 is mainly found in the Neotropical region. Seven of 28 taxonomically described species have been reported from Argentina. Chromosome studies performed on this genus showed a wide variation in chromosome number and a high frequency of the neoXY chromosomal sex-determination system, although the sexual pair was not observed in all cases. This work analyzes the spermatogenesis of Orthemisdiscolor (Burmeister, 1839), O.nodiplaga Karsch, 1891 and O.ambinigra Calvert, 1909 in individuals from the provinces of Misiones and Buenos Aires, Argentina. Orthemisdiscolor has 2n=23, n=11+X and one larger bivalent. Orthemisnodiplaga exhibits the largest chromosome number of the order, 2n=41, n=20+X and small chromosomes. Orthemisambinigra shows a reduced complement, 2n=12, n=5+neo-XY, large-sized chromosomes, and a homomorphic sex bivalent. Fusions and fragmentations are the main evolutionary mechanisms in Odonata, as well as in other organisms with holokinetic chromosomes. Orthemisnodiplaga would have originated by nine autosomal fragmentations from the ancestral karyotype of the genus (2n=22A+X in males). We argue that the diploid number 23 in Orthemis has a secondary origin from the ancestral karyotype of family Libellulidae (2n=25). The complement of O.ambinigra would have arisen from five autosomal fusions and the insertion of the X chromosome into a fused autosome. C-banding and DAPI/CMA3 staining allowed the identification of the sexual bivalent, which revealed the presence of constitutive heterochromatin. We propose that the chromosome with intermediate C-staining intensity and three medial heterochromatic regions corresponds to the neo-Y and that the neo-system of this species has an ancient evolutionary origin. Moreover, we discuss on the mechanisms involved in the karyotypic evolution of this genus, the characteristics of the neo sex-determining systems and the patterns of heterochromatin distribution, quantity and base pair richness.

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.

Cytogenetic studies of three Lycosidae species from Argentina (Arachnida, Araneae)

Cytogenetic studies of the family Lycosidae (Arachnida: Araneae) are scarce. Less than 4% of the described species have been analyzed and the male haploid chromosome numbers ranged from 8+X1 X 2 to 13+X1 X 2. Species formerly classified as Lycosa were the most studied ones. Our aim in this work was to perform a comparative analysis of the meiosis in "Lycosa" erythrognatha Lucas, "Lycosa" pampeana Holmberg and Schizocosa malitiosa (Tullgren). We also compared male and female karyotypes and characterized the heterochromatin of "L." erythrognatha. The males of the three species had 2n = 22, n = 10+X1X2, all the chromosomes were telocentric and there was generally a single chiasma per bivalent. In "Lycosa" pampeana, which is described cytogenetically for the first time herein, the bivalents and sex chromosomes showed a clustered arrangement at prometaphase I. The comparison of the male/female karyotypes (2n = 22/24) of "Lycosa" erythrognatha revealed that the sex chromosomes were the largest of the complement and that the autosomes decreased gradually in size. The analysis of the amount, composition and distribution of heterochromatin with C-banding and staining with DAPI- and CMA3 - showed that "Lycosa" erythrognatha had little GC-rich heterochromatin in the pericentromeric region of all chromosomes. In addition, the actual occurrence of the genus Lycosa in the Southern Hemisphere is discussed.