Oecomys, Thomas, 1906

Moreira, Camila Do Nascimento, Ventura, Karen, Percequillo, Alexandre Reis & Yonenaga-Yassuda, Yatiyo, 2020, A review on the cytogenetics of the tribe Oryzomyini (Rodentia: Cricetidae: Sigmodontinae), with the description of new karyotypes, Zootaxa 4876 (1), pp. 1-111 : 56

Oecomys sp. 1

Karyotype: 2n = 54 and FN = 84. Autosomal complement: 16 biarmed pairs large to small decreasing in size, and 10 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a large acrocentric; Y, a medium submetacentric ( Fig. 14A ). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of autosomal pairs. One medium submetacentric pair presented a pericentromeric heterochromatin block that extend to the short arm and one small acrocentric pair presented an interstitial C-band on its long arm. The X chromosome presented a conspicuous pericentromeric heterochromatic block and an interstitial lightly stained C-band on its long arm. The Y chromosome was almost entirely heterochromatic ( Fig. 14B ). Gbanding was performed to allow the correct identification of all homologous pairs ( Fig. 14C ). FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed ( Fig. 14D ). We compare the karyotype of Oecomys sp. 1 (2n = 54, FN = 84) with O. rutilus (2n = 54, FN = 90) from Rio Negro, Amazonas state of Brazil. These two complements differ mainly by the presence of three medium to small acrocentric pairs in Oecomys sp. 1, instead of three biarm pairs in O. rutilus , and by the morphology of X chromosome. Also, the karyotype of Oecomys sp. 1 presents more conspicuous heterochromatic C-band than O. rutilus . The G-band patterns between the two karyotype were equally distinct. Based on these comparative analyses, we suggested that the species mentioned here as Oecomys sp. 1 was distinctly from O. rutilus . In addition, the same diploid and fundamental number of Oecomys sp. 1 was mentioned by Gomes-Júnior et al. (2016) (unpublished data from T. Lira). However, as these authors provided no additional information, a more thorough comparison was not possible. Nevertheless, as the karyotype mentioned by Gomes-Júnior et al. (2016) were from populations from Rio Cuieiras, Amazonas state of Brazil, it was likely that they may belong to the same species.

Figures

FIGURE 14. Karyotype of Oecomys sp. 1, male with 2n = 54 and FN = 84. (A) Conventional staining (ICA 238); (B) C-banding (ICA 238); (C) G-banding (ICA 238); (D) Metaphase plate after fluorescent in situ hybridization with telomeric probe (left) and DAPI staining (right) (ICA 238).