Euryoryzomys macconnelli (Thomas, 1910)

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 : 15-16

Euryoryzomys macconnelli

Karyotype: 2n = 64 and FN = 64, according to Gardner & Patton (1976), who originally described this karyotype for Peruvian samples, the chromosomal preparation from the only specimen examined did not permit unequivocal identification of the morphologies of all the chromosomes. Nevertheless, the diploid number was clearly 64 and the karyotype appears to consists of one small metacentric pair and 31 acrocentric pairs large to small decreasing in size. Since it was unlikely that the small metacentric pair represent the sex chromosome, the X and Y were probably acrocentric and the FN was given as 64 ( Gardner & Patton 1976, pp. 8). The same karyotype was reported some years later by Silva et al. (2000, pp. 224) for samples from Mato Grosso, Brazil.

The same diploid number was described by Musser et al. (1998, pp. 231, Fig. 105) for populations from western Brazil, with a different fundamental number. Karyotype: 2n = 64 and FN = 70. Autosomal complement: four medium to small metacentric and submetacentric pairs, and 27 acrocentric pairs large to small decreasing in size. Sex chromosomes: X, a large subtelocentric; Y, a small acrocentric ( Musser et al. 1998). According to the authors, the karyotype of the Peruvian specimen, reported by Gardner & Patton (1976) has the same diploid number, but because the Brazilian animals have four pairs of biarmed autosomes instead of the single pair reported for the Peruvian animal, the fundamental number was 70 instead of 64. Additional preparations from Peruvian specimens may show the reported differences to be an artefact of the poor quality of original chromosomal slides ( Musser et al. 1998).

The specimens collected in Venezuela by Musser et al. (1998, pp. 231, Fig. 105) presented another different karyotype. Karyotype: 2n = 76 and FN = 85. Autosomal complement: five small metacentric and submetacentric pairs, 31 acrocentric pairs large to small decreasing in size, and two unpaired chromosomes, a medium-sized metacentric and a medium-sized acrocentric. Sex chromosomes: X, a large subtelocentric; Y, a small acrocentric. According to the authors, several pairs of acrocentric autosomes bear discernible second arms and could be classed as biarmed chromosome, thus raising the FN to as high as 107 ( Musser et al. 1998).

Another different karyotype was mentioned by Patton et al. (2000, pp. 143), from samples for Rio Jaú, Amazonas. Karyotype: 2n = 58 and NF = 90, the information was not available in literature, as Patton et al. (2000) informed that this represents unpublished data provided by M.N.F. Silva. These variation in diploid and fundamental number of E. macconnelli occurs in different localities of Amazon rainforest ( Table 3, Fig. 3 ).

Figures

FIGURE 3. Distribution of diploid and fundamental number of karyotyped specimens of genus Euryoryzomys. (■) E. emmonsae; (□) E. lamia; (▲) E. macconnelli; (○) E. nitidus; (l) E. russatus; (r) Euryoryzomys sp. nov.; (ê) Euryoryzomys sp..