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Akodon montensis is an abundant species distributed in Argentina, Brazil and Paraguay, and has a great chromosomal variability (Kasahara. J Parasitol. Apr;83(2) Besnoitia sp. (Protozoa:Toxoplasmatinae) from Akodon montensis (Rodentia:Cricetidae) in Santa Catarina State, Brazil. Range Description. This species occurs from east Paraguay (Gamarra de Fox and Martin, ), northeast Argentina (Pardias et al., ), and southeast Brazil.

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Individuals from 1 to 10 had no supernumerary chromosome and from 11 to 14 had the B chromosome. The genus Akodon Meyen, is one of the most species-rich among sigmodontine rodents and has great chromosome variability.

Montane grass mouse

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.

Additionally, two XY females and two variants of the X montsnsis 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 qkodon regions. The genus Akodon Meyen,with about 41 species, is considered one of the most species-rich group within the subfamily Sigmodontinae. Its species are widely distributed in South America and inhabit a variety of habitats, among subtropical and tropical moist forest as well as desert regions Musser and Carleton From a taxonomic point akofon view, the genus includes morphologically very similar species, and cytogenetic data is valuable for identifying them, such as Akodon cursor Winge, and Akodon montensis Yonenaga-Yassuda et al.

Akodon montensis is an abundant species distributed in Argentina, Brazil and Paraguay, and has a great chromosomal variability Kasahara and Yonenaga-Yassuda ; Musser and Carleton However, for animals from Brazil, Kasahara and Yonenaga-Yassuda described a morphological variation for the X chromosome, which was present in both sexes.

Additionally the presence of supernumerary or B chromosomes was reported for specimens from Brazil Yonenaga-Yassuda et al. Cytogenetic data on natural populations of Akodon montensis in Argentina are scarce. A total of 31 specimens of Akodon montensis 18 females and 13 males were collected from five localities of Misiones Province, Argentina Fig.

Chromosome preparations were obtained from bone marrow and testes Ford and Hamerton ; Evans et al.

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Ten metaphase spreads were counted for each specimen, except in the individual with trisomy in which we counted The distribution of constitutive heterochromatin C-bands was determined according to Sumner method. Map indicating a collection sites of Akodon montensis in the province of Misiones, Argentina analyzed in this work: All individuals of Akodon montensis had an autosome complement composed of nine pairs of large to medium size metacentric chromosomes, and two small-sized pairs, one acrocentric and one metacentric.

Mitotic chromosomes of Akodon montensis: Five specimens four females and one male had 25 chromosomes in all analyzed cells due to the presence of a small submetacentric B chromosome Fig. The supernumerary chromosome was found in the five localities, representing Sampling localities of Akodon montensis analyzed in this work.


The Y chromosome was small acrocentric. The X was a medium-sized chromosome and showed two morphological variants: From eighteen females, nine Variants of sex chromosomes in the females of Akodon montensis with Giemsa staining: Acrocentric and subtelocentric variants of X chromosome had positive C-bands in the pericentromeric regions Fig. Additionally, the subtelocentric X chromosome presented a large positive C-band, which covered its short arm Fig.

The Y chromosome was completely heterochromatic Fig. B chromosome of Akodon montensis: Ag-NORs were evident in the distal position of pairs 2, 4, 6, 7 and 10 Fig.

However, the number of positive signals varied between two and seven in different cells See Suppl. The total number of positive Ag-NORs was different between cells with B four specimens, 36 cells, mean 5. The exclusion of the supernumerary chromosome from the analysis resulted in no statistically significant difference in the number of active NORs in autosomes in cells with mean 4.

In addition, we observed a cell in which the X and Y chromosome were dissociated Fig. Diakinesis cells of an individual with trisomy and one B chromosome: The studied populations of Akodon montensis from Brazil showed high chromosome variability Kasahara and Yonenaga-Yassuda ; Fagundes et al. However in Argentina, with a low sample size, no karyotype variation had been detected previously Liascovich and Reig In this work we found the same variability described in Brazil, which involve the presence of a B chromosome, X chromosomes variants and seeming XY females.

Constitutive heterochromatin CH is in mammals, and particularly in rodents, an important source of karyotype variability Graphodatsky et al.

Akodon montensis has small positive C-bands in the pericentromeric regions of all chromosomes Kasahara and Motnensis ; this workwhich is common in Akodon species, and in rodents in general Ortiz et al. Our results of DAPI staining showed high homology among karyotypes of specimens from Argentina and those for Brazil studied with G-banding method Fagundes and Yonenaga-Yassuda ; Silva and Yonenaga-Yassudawhich indicates a high conservation in the standard karyotype of this abundant and widely distributed species.

However, certain species depart from this pattern Graphodatsky et al. In our sample akkodon females presented heteromorphic sex chromosomes XY. In Akodon montensis from Brazil the occurrence of XY female was confirmed with molecular cytogenetic techniques Fagundes et al.

Even though, in Akodon montensis this condition has a relative low frequency Fagundes et al. In Brazil and Argentina, two morphologies for the X chromosome were observed: This polymorphism has three possible combinations in females: The XsXs found in one female is reported for the first time. Females with XaXa were the most frequent in specimens studied here Additionally, XY females with different types of X chromosomes were detected in both countries Fagundes et al.

In males, we observed only the Xa; but in Brazilian populations males with both X types were found Kasahara and Yonenaga-Yossuda Thus, the data suggest differences in the frequencies of X chromosome variants among populations, but larger sample sizes are needed to validate these observations. Sex chromosomes of several rodents showed variation in the amount and distribution of heterochromatin Patton and Sherwood In this work both Xa and Xs presented CH in the pericentromeric regions.

Additionally, the short arms of Xs had positive Montensix. However, the data from different localities of Brazil are akkodon. Some authors detected the same pattern described here Fagundes et al. The Y chromosome of Akodon montensis from Argentina was completely heterochromatic.


The same pattern was observed in several mammals, and particularly in individuals of Akodon montensis from Brazil Kasahara and Yonenaga-Yassuda ; Waters et al. Although, Fagundes et al. The B of Akodon montensis studied here had identical morphology to those detected in Brazil Yonenaga-Yassuda et al. However, the described C- and G-banding patterns varied in different studies. Some authors akodpn the B chromosome as slightly heterochromatic and uniformly G-banded Kasahara and Yonenaga-Yassuda ; Silva and Yonenaga-Yassuda ; while others reported it as almost heterochromatic with conspicuous pericentromeric C-bands Kasahara CH patterns on Bs have been extensively studied in some species of rodents, in which most often appear as almost completely heterochromatic.

In Akodon montensisthe described patterns suggest that different polymorphisms for B chromosomes may be coexisting in this species. In Akodon montensis the B chromosome showed NORs at the end of both arms, which are also coincident with the location of rDNA detected by fluorescent in situ hybridization Kasahara These observations support the hypothesis that different B chromosomes can be present in Akodon montensis. In Akodon montensis the frequency of individuals with Bs appears to vary among localities, but several populations were studied with low sample size.

In this work individuals with more than one B were not identified. This chromosome was stable in mitoses and meioses, since no evidence for accumulation or elimination were detected. Finally, in the present paper we report for the first time a trisomy of chromosome 11 in a single individual. In Akodon cursor also were observed an individual with trisomy for chromosome 7 Fagundes et al. No phenotypic malformations were detected in both cases.

However the frequency of trisomies in natural populations and the biological consequences of monfensis condition have not been investigated yet. In conclusion, chromosome data for Akodon montensis showed high variability in all studied populations throughout its geographic range. However, additional data are needed to understand the dynamic of the multiple chromosome polymorphism observed in this species of sigmodontine rodents.

We thank to Marcelo Cavicchia and to several members of the LGE for the cooperation in the fieldwork. We are grateful to the reviewers for a critical revision of an early version of this paper.

Aodon Cytogenetics 10 1: National Center for Biotechnology InformationU. Journal List Comp Cytogenet v. Published online Feb 2. Author information Article notes Copyright and License information Disclaimer. Carolina Alicia Labaroni moc. Received Aug 31; Accepted Nov 5. This article has been cited by other articles in PMC.

Associated Data Supplementary Materials Supplementary material 1: This dataset is made available under the Open Database License http: The Open Database License ODbL is a license agreement intended to akoon users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author s are credited. Abstract The genus Akodon Meyen, is one of the most species-rich among sigmodontine rodents and has great chromosome variability.

Rodents, karyotype variability, chromosome banding, heterochromatin, Ag-NORs. Introduction The genus Akodon Meyen,with about 41 species, is considered one of the most species-rich group within the subfamily Sigmodontinae.