Phyllotis xanthopygus (Waterhouse, 1837) is an Andean rodent endemic to South America. Despite its wide geographical distribution in Argentina, few individuals have been studied on the cytogenetic level and only through conventional staining. In this work, chromosome characterization of Argentine samples of this species was performed using solid staining, C-banding and base-specific fluorochromes. Twenty two specimens were analyzed, collected in the provinces of Jujuy, Catamarca, and the north and south of Mendoza. All studied specimens showed 2n=38, having mostly the bi-armed autosomes, metacentric or submetacentric. Fundamental Number varied between 70 and 72. These changes were due to the presence of chromosome heteromorphisms in individuals from southern Mendoza and Jujuy. C-banding revealed pericentromeric blocks of constitutive heterochromatin in most chromosomes. Acrocentric chromosomes involved in heteromorphisms showed high variation in the amount of heterochromatin within and among populations. Additionally, banding with fluorochromes (DAPI and chromomycin A3) revealed homologous localization of AT and GC rich regions among chromosomes of the different populations analyzed. Comparisons among heteromorphic pairs suggested, however, that the variation might be the result of complex chromosome rearrangements, involving possibly amplifications and/or deletions of heterochromatic segments. These results are in accordance with molecular studies that indicate genetic variability within and among the populations of this taxon.

Phyllotines are sigmodontine rodents endemic to South America with broad genetic variability, Robertsonian polymorphisms being the most frequent. Moreover, this taxon includes a species with multiple sex chromosomes, which is infrequent in mammals. However, molecular cytogenetic techniques have never been applied to phyllotines to elucidate their karyotypic evolution. We studied the chromosomes of 4 phyllotine species using FISH with a pantelomeric probe (TTAGGG)_n. Graomys griseoflavus, Eligmodontia puerulus, and E. morgani are polymorphic for Robertsonian translocations, whereas Salinomys delicatus possesses XX/ XY₁Y₂ sex chromosomes. Telomeric signals were detected at both ends of all chromosomes of the studied species. In S. delicatus interstitial telomeric sequences (ITS) were observed in the 3 major chromosome pairs, which are equidistant from one of the telomeres in these chromosomes. These results suggest that ITS are important in the reshuffling of the highly derived karyotype of S. delicatus. Considering the phylogeny of phyllotines, the Robertsonian rearrangements of G. griseoflavus, E. puerulus, and E. morgani possibly represent chromosome fusions which have occurred independently. The pericentromeric regions of the biarmed chromosomes of these species do not contain telomeric sequences characteristic for strict fusions of recent origin, suggesting a common pattern of telomeric repeat loss during chromosomal evolution of these rodents.

The genus Ctenomys comprises about 70 species with great chromosome diversity. The Corrientes group is one of the most chromosomally variable lineages in the genus, where the diploid number (2n) varies from 41 to 70. In this group, three nominal species and numerous polymorphic and polytypic populations have been described. In order to get insight into the chromosomal evolution of this species complex, we applied different banding and molecular cytogenetic techniques. The results were interpreted in an evolutionary context, based on mitochondrial cytochrome b analyses. Studied samples are representative of the broad chromosomal variability in the group, including specimens with 2n = 42 to 2n = 70. Heterochromatin was scarce but concentrated in a few chromosomes. Centromeric DAPI-negative heterochromatin was observed in some autosomal pairs, which differed among populations. Location and amount of DAPI-neutral heterochromatin within the Y chromosome varied among populations. The variable distribution of heterochromatin indicates its dynamic behavior. NORs were detected in one pair of autosomes, which also differed among some populations. Telomeric FISH signals were observed in all complements only at the chromosome ends. The Corrientes group belongs to a clade that also includes C. pearsoni, C. lami, C. minutus, C. ibicuiensis and C. torquatus. Almost all of these species are variable at the chromosomal level, suggesting that this is the ancestral condition of the clade. Within the Corrientes group, the observed low genetic divergence, in contrast with its high chromosomal variability, is indicative of decoupling between the rates of chromosomal and mitochondrial evolution.

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Glyphonycteris is a poorly known genus of bats that inhabit lowlands and forested mountains of Central and South America. This genus comprises three nominal species, with G. sylvestris being the most widely distributed species in South America. The karyological data previously available for this genus are restricted to those resulting from conventional staining techniques applied to a few specimens from Surinam. Here, we report the rst record of G. sylvestris in Argentina extending its southern distribution. Moreover, our new locality represents the seventh record from the Atlantic Forests Biome and the rst from Araucaria Moist Forest ecoregions. Our specimen overall exhibits the diagnostic characteristics described for the species except for some di erences in the distribution of hairs on the wings and limbs. The fecal sample obtained from our specimen contained only seeds of Piper aduncum. The karyotype was 2n = 22 with a FN = 42; the analysis of uorochrome banding patterns in the chromosomal pericentromeric regions shows DAPI (4,6-diamidino-2-phenylindole) positive blocks in pairs 5 and 8, whereas pericentromeric regions stained with CMA3 (Chromomicine A3) are positive in pairs 1, 2, 3, 4 and 11. Moreover, the interstitial region of chromosomes shows DAPI and CMA3 positive blocks in pairs 1, 2, 3, 4 and 5. These karyological data are novel to G. sylvestris, contributing to the scarce knowledge of the genus. Thus, lling blanks of information and enabling further comparative chromosome analysis.RESUMEN. Primer registro de Glyphonycteris sylvestris Thomas, 1896 (Chiroptera: Phyllostomidae: Glyphonycterinae) para Argentina, con comentarios sobre su cariotipo. Glyphonycteris es un género poco conocido de murciélago que habita los bosques de tierras bajas y de montañas de Centroamérica y Sudamérica. Este género incluye tres especies nominales; donde G. sylvestris es la más ampliamente distribuida al sur de Sudamérica. Los datos de cariotipo para este género están restringidos a técnicas de tinción convencional realizadas sobre unos pocos especímenes de Surinam. En este trabajo se presenta el primer registro de G. sylvestris en Argentina extendiendo su distribución sur. Además, esta nueva localidad representa el séptimo registro para el Bioma del Bosque Atlántico y el primero para la ecorregión de los Bosques Húmedos de Araucaria. Nuestro espécimen exhibe los caracteres diagnósticos para la especie excepto por algunas diferencias en la distribución de los pelos en alas y miembros. La muestra fecal obtenida de nuestro espécimen solo contenía semillas de Piper aduncum. El cariotipo tuvo un 2n = 22 y FN = 42; los patrones de bandeo con uorocromos en la región pericentromérica muestra bloques de DAPI (4,6-diamino-2-fenilindol) positivo en los

Eligmodontia is a genus of phyllotine rodents adapted to arid environments with seven recognized species. The sister species E. puerulus and E. moreni are distributed in the adjacent highland Puna and lowland Monte deserts respectively, and show remarkable morphological and chromosomal differences. However, analyses of the cytochrome b gene showed important variability, without reciprocal monophyly between them. In order to study the evolutionary processes involved in the diversification of both taxa, we analyzed 1161 bp of the mitochondrial control region and flanking sequences (N=60), as well as 759 bp of the first exon of the nuclear gene IRBP (N=14). Individuals of both species from Jujuy, Catamarca and Mendoza Provinces of Argentina were previously karyotyped.Results showed that the mitochondrial sequences present high haplotype and nucleotide diversity within all population, and no haplotype was shared between both species. FST indicated that populations of both species were moderately structured. The network was constituted by two major haplogroups, one composed by E. puerulus samples from Jujuy, and the other composed of sequences of all studied populations. The Bayesian analysis showed three clusters, matching the network. Phylogenetic analysis recovered two clades with high support, in coincidence with the network groups. There was only one close join between sequences of both species, corresponding to samples from Catamarca. Thus, mitochondrial data suggested hybridization between both species in Catamarca, with asymmetric introgression. The IRBP showed low variability and, in the phylogenetic analysis, the sequences of E. puerulus form a monophyletic group with intermediate support, whereas those of E. moreni collapse into a basal polytomy. Our data indicated a recent divergence and absence of introgression in the nuclear genomes. The results at the population level with mitochondrial sequences, together with integrative taxonomy at the species level in a biogeographic context, suggest that climatic and geologic changes could have had an important role in the determination of genetic variability patterns observed in these rodents.

The genus Akodon Meyen, 1833 is one of the most species-rich among sigmodontine rodents and has great chromosome variability. Akodon montensis has a relatively broad distribution in South America, and Argentine populations are located in the southernmost region of its range. Brazilian populations have important chromosomal variability, but cytogenetic data from Argentina are scarce. We performed a chromosome characterization of natural populations of Akodon montensis using conventional staining, C-banding, Ag-NORs and base-specific fluorochromes. A total of 31 specimens from five localities of Misiones Province, in Argentina, were analyzed. The 2n=24 chromosomes was the most frequently observed karyotype. However, five individuals presented 25 chromosomes due to a supernumerary B-chromosome; and one individual had 2n=26 due to one B plus a trisomy for chromosome 11. Additionally, two XY females and two variants of the X chromosomes were found. C-positive centromeric bands occurred in all chromosomes; additional C-bands were observed in some autosomes, the X, Y and B chromosomes. Ag-NORs were observed in five autosomes, and the B chromosome was frequently marked. Fluorochrome banding was similar among karyotypes of the analyzed populations. Comparisons of cytogenetic data among populations of Argentina and Brazil showed the presence of high intraspecific variability in Akodon montensis and some differences among regions.

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