The Amazonian brown brocket Mazama nemorivaga (Cuvier, 1817) is a small to medium-sized deer from the Amazon rainforest and ecotones. The first karyotype described was 2n=67 to 69 + 2-7 B and FN= 69-72, in which all chromosomes were acrocentric and the X chromosome was the only submetacentric chromosome. However, important aspects of the species chromosome evolution were not resolved because of the lack of information on chromosome banding. The G-banding pattern of Mazama nemorivaga karyotype showed the presence of an XX/XY1Y2 sex chromosome system as a product of an X-autosome tandem fusion, which results in a basic 2n=68, FN=70 in females and 2n= 69, FN=70 in males. The fact that this karyotype only differs from that of Capreolus capreolus pygargus (Pallas, 1771; 2n=70, FN=72+B) by X-autosome tandem fusion may corroborate the basal condition of Mazama nemorivaga and its proximity to the ancestral karyotype of the American Odocoileini. A derived karyotype 2n=67, XY1Y2, FN=70 + 3B from the Brazilian state of Mato Grosso (the western Amazon) may be evidence of differentiation between western and eastern populations.
ABSTRACT. The tendency toward chromosome fragility is one of the theories that may explain chromosome variation in brocket deer species (genus Mazama). We tested doxorubicin as an inducer of chromosome aberrations in lymphocytes of three brocket deer species, Mazama gouazoubira, M. americana and M. nana, compared to the marsh deer, Blastocerus dichotomus. Doxorubicin, at a concentration of 0.25 µg/mL, induced chromosome aberrations and fragile sites in all four species; the highest frequencies were seen in M. gouazoubira; they were lowest in B. dichotomus and intermediate in M. americana and M. nana. These results were expected based on previous karyotypic studies, but they failed to explain the higher sensitivity seen in M. gouazoubira. This may be because not all the aberrations and fragile sites are related to chromosome evolution in brocket deer; other factors, such as environmental influences, may be involved in chromosome fragility.
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