Oecomys auyantepui

Oecomys auyantepui

Two different karyotypes were reported by Gomes-Júnior et al. (2016, pp. 409, Fig. 2, and pp. 410, Fig. 3) who characterized them as karyomorph ‘a’ and karyomorph ‘b’. Karyomorph ‘a’: 2n = 64 and FN = 110. Autosomal complement: eight metacentric pairs large to small decreasing in size, three submetacentric pairs (two large and one small), 13 subtelocentric pairs large to small decreasing in size, and seven small acrocentric pairs. Sex chromosomes: X and Y were medium submetacentrics. Karyomorph ‘b’: 2n = 66 and FN = 112. Autosomal complement: six metacentric pairs (two large and four small), five submetacentric pairs (two large and three small), 13 subtelocentric pairs medium to small decreasing in size, and eight small acrocentric pairs. Sex chromosomes: X, a large metacentric; Y, a medium submetacentric. C-banding metaphases, in both karyotypes, exhibited blocks of constitutive heterochromatin, ranging between subtle and conspicuous, on the pericentromeric region of all autosomes. The X chromosome presented a pericentromeric heterochromatic blocks and a lightly stained C-band on both telomeric regions. The Y chromosome presented the long arm entirely heterochromatic. G-banding was also performed. NORs were localized at the telomeric regions of the short arms of one medium and one small autosomal pair of both karyotypes. FISH with 18S rDNA revealed signals at the telomeric regions of short arms in one medium and one small autosomal pair in both karyotypes, while FISH with 5S rDNA revealed signals at the pericentromeric region of one large pair of karyomorph ‘a’, and one medium pair of karyomorph ‘b’. FISH with telomeric sequences revealed signals at the ends of all chromosomes, and additional telomeric sequences was found on the pericentromeric region of X chromosome in both karyotypes. Another karyotype, with 2n = 72 and FN = 80, was attributed to this species by Gomes-Júnior et al. (2016) (unpublished data from T. Lira) based on molecular data. However, this karyotype was very distinct from that presented by Gomes-Júnior et al. (2016). In addition, the karyotypes presented by Gomes-Júnior et al. (2016) occurs sympatrically on specimens collected in Amazonas, state of Brazil, whereas the karyotype reported by T. Lira (unpublished data) occurs in specimens collected in Pará, state of Brazil (Table 8, Fig. 12). We suggested a more detailed analyses, using morphological and molecular data combined, in the specimen studied by T. Lira, in order to correctly identify this specimen.