Zygodontomys brevicauda

Zygodontomys brevicauda (= Z. b. microtinus)

The karyotype of 2n = 78 was reported by Tranier (1976) based on a sample from French Guiana (Table 11), but the author did not describe or illustrate the karyotype. Another karyotype was reported by Mattevi et al. (2002, pp. 36, Fig. 2) and Bonvicino et al. (2009). Karyotype: 2n = 86 and FN = 96 to 100. Autosomal complement: two large submetacentric and subtelocentric pairs, four or five medium to small biarmed pairs, and the remaining being acrocentric. Sex chromosomes: X, a large submetacentric; Y, a medium subtelocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of the autosomes, being usually absent on the two large autosomal pairs. The short arm of the X and the whole Y chromosomes were heterochromatic. G-banding was also performed. NORs, were localized at the short arms of one medium and one small acrocentric pairs, but in two metaphase plates a third pair, a medium acrocentric, showed a NORs on its long arm.

According to Bonvicino et al. (2009), the Brazilian populations of Zygodontomys presents, at least, three karyotypes reported, indicating that the diversity of this genus was underestimated in Brazil and suggesting the existence of several evolutionary lineages. Molecular phylogenetic analyses recovered three major clades congruent with known karyotypes, indicating the existence of three species, two of which currently undescribed, mentioned by the authors as Zygodontomys sp. 1 and Zygodontomys sp. 2, whose karyotypes were described below. According to Voss (2015), a more comprehensive revisionary work for the genus is still pending.