Nephelomys meridensis (Thomas, 1894)

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 : 46-47

Nephelomys meridensis

Karyotype: 2n = 66 and FN = 104. Autosomal complement: one medium subtelocentric pair, 19 metacentric and submetacentric pairs medium to small decreasing in size, and 12 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X chromosome presented two different morphologies, a medium metacentric, and a medium acrocentric; Y, a small subtelocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, with the exception of four biarmed pairs which little or no centromeric heterochromatin was found, in addition, some acrocentric pairs presented a lightly stained C-band on distal regions of its long arm. The both X chromosome presented two heterochromatic blocks, one pericentromeric and another distal. The Y chromosome was totally heterochromatic in both cases. G-banding was also performed ( Aguilera et al. 1995, pp. 46, Fig. 2B ).

Another karyotype was also presented by Aguilera et al. (1995), for the samples of western Venezuela, from the Páramo de Tamá. Although distinct from N. meridensis on morphological and karyological traits, specimens of this region were provisionally identified as N. meridensis ( Percequillo 2015e) , until subsequent analyses validate or reject this hypothesis. Karyotype: 2n = 66 and FN = 92. Autosomal complement: one medium subtelocentric pair, 13 metacentric and submetacentric pairs medium to small decreasing in size, and 18 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a medium acrocentric; Y, unknown as only a female was examined. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, some acrocentric pairs presented a lightly stained C-band on distal regions of its long arm. The X chromosome presented two heterochromatic blocks, one pericentromeric and another distal. G-banding was also performed ( Aguilera et al. 1995, pp. 46, Fig. 2A ).

Aguilera et al. (1995) analyzed by G-banding these two karyotypes and suggested that the difference in the number of chromosomal arms was possible to be explained due the occurrence of pericentric inversions.

Figures

FIGURE 2. Distribution of diploid and fundamental number of karyotyped specimens of genus Cerradomys. (□) C. akroai; (■) C. goytaca; (ê) C. langguthi; (r) C. maracajuensis; (▲) C. marinhus; (○) C. scotti; (☆) C. subflavus; (l) C. vivoi.