Neacomys, Thomas, 1900

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 : 34

Neacomys sp.

Cytotype 1: 2n = 58 and FN = 70. Autosomal complement: seven medium metacentric and submetacentric pairs, and 21 acrocentric pairs. Sex chromosomes: X, a medium submetacentric; Y, a small submetacentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, on two biarmed pairs the heterochromatic blocks were bigger, and other three biarmed were almost heterochromatic. The X chromosome presented the short arm entirely heterochromatic. The Y chromosome was almost entirely heterochromatic ( Silva et al. 2015, pp. 4, Fig. B1 ; Silva et al. 2019).

Cytotype 2: 2n = 58 and FN = 64. Autosomal complement: four small metacentric pairs, and 24 acrocentric pairs. Sex chromosomes: X, a medium submetacentric; Y, a small submetacentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, and three biarmed pairs were almostly heterochromatic. The X chromosome presented the short arm entirely heterochromatic. The Y chromosome was almost entirely heterochromatic ( Silva et al. 2015, pp. 4, Fig. B2 ). These two cytotypes occurs in different localities of Pará, state of Brazil ( Silva et al. 2015; Silva et al. 2019). G-banding was also performed. FISH with 18s rDNA sequences revealed signals of NORs on the distal region of the long arm of three autosomal pairs, one metacentric and two small acrocentric pairs of both cytotypes. FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed in either cytotypes ( Silva et al. 2015). Silva et al. (2019) established maps of chromosomal homology between cytotype 1, and cytotype 2 of Neacomys sp., by using whole chromosome probes of H. megacephalus . The comparative genomic mapping showed that these cytotypes differs by the presence of blocks of constitutive heterochromatin on the short arms of metacentric chromosomes 22, 23, and 26 of cytotype 1, that was absent on acrocentric chromosomes 22, 24, and 23 of cytotype 2. Di-Nizo et al. (2017) also reported a diploid number of 58 for a Neacomys species from Mato Grosso, state of Brazil, with a different fundamental number of 66 ( Di-Nizo et al. 2017, pp. 859, Fig. 1 ).

Figures

FIGURE 1. Collection localities of Oryzomyini species analyzed in this work. (1) Claúdia, Mato Grosso state; (2) and (3) Rio Japurá, Amazonas state; (4) and (5) Rio Içá, Amazonas state.

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.