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 : 57

Oecomys sp. 2

Karyotype: 2n = 64 and FN = 92. Autosomal complement: 15 biarmed pairs large to small decreasing in size, and 16 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a large subtelocentric; Y, a medium acrocentric ( Fig. 15A ). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of autosomal pairs. The X chromosome presented the short arm entirely heterochromatic. The Y chromosome was almost entirely heterochromatic ( Fig. 15B ). G-banding was performed to allow the correct identification of all homologous pairs ( Fig. 15C ). FISH with telomeric sequences revealed signals at the ends of all chromosome arms, and additional telomeric sequences was found on the pericentromeric region of one medium submetacentric pair ( Fig. 15D ). We compare the karyotype of Oecomys sp. 2 (2n = 64, FN = 92) with O. auyantepui (2n = 64, FN = 110) from Rio Jatapú, Amazonas state of Brazil. These two complements were distinct mainly by the presence of nine acrocentric pairs in Oecomys sp. 2, instead of nine biarm pairs in O. auyantepui , and by the morphology of sex chromosome. Also, the karyotype of Oecomys sp. 2 presents more conspicuous heterochromatic C-band than O. auyantepui . The G-band patterns between the two karyotypes were equally distinct. In addition, Oecomys sp. 2 presented an interstitial telomeric sequence on the pericentromeric region of one medium submetacentric pair, while O. auyantepui presented an interstitial telomeric sequence on the centromeric region of the X chromosome. Based on these comparative analyses, we suggested that the species mentioned here as Oecomys sp. 2 was distinctly from O. auyantepui .

Figures

FIGURE 15. Karyotype of Oecomys sp. 2, female with 2n = 64 and FN = 92. (A) Conventional staining (JAP 150) (inset: sex chromosomes of a male (JAP 96)); (B) C-banding (JAP 150) (inset: sex chromosomes of a male (JAP 96)); (C) G-banding (JAP 150); (D) Metaphase plate after fluorescent in situ hybridization with telomeric probe (left) and DAPI staining (right) (JAP 150), arrows indicate the hybridization of interstitial telomeric sequence.