Abstract
We investigated the karyotype of 18 didelphid species captured at 13 localities in the Brazilian Amazon, after conventional staining, C-banding, Ag-NOR and fluorescent in situ hybridization (FISH) using the 18S rDNA probe. Variations were found in the X chromosome, heterochromatin distribution and the 18S rDNA sequence. The main variation observed was in the position of the centromere in the X chromosome of Caluromys philander Linnaeus, 1758 and Marmosa murina Linnaeus, 1758. For both species, the X chromosome showed a geographical segregation in the pattern of variation between eastern and western Brazil, with a possible contact area in the central Amazon. C-banding on the X chromosome revealed two patterns for the species of Marmosops Matschie, 1916, apparently without geographic or specific relationships. The nucleolus organizer region (NOR) of all species was confirmed with the 18S rDNA probe, except on the Y chromosome of Monodelphis touan Shaw, 1800. The distribution of this marker varied only in the genus Marmosa Gray, 1821 [M. murina Thomas, 1905 and M. demerarae Thomas, 1905]. Considering that simple NORs are seen as a plesiomorphic character, we conclude that the species Marmosa spp. and Didelphis marsupialis Linnaeus, 1758 evolved independently to the multiple condition. By increasing the sample, using chromosomal banding, and FISH, we verified that marsupials present intra- and interspecific chromosomal variations, which suggests the occurrence of frequent chromosomal rearrangements in the evolution of this group. This observation contrasts with the chromosomal conservatism expected for didelphids.
Highlights
In the Americas, subclass Metatheria Huxley, 1880 is represented by the three marsupial orders: Didelphimorphia Gill, 1872, Paucituberculata Ameghino, 1894 and Microbiotheria Ameghino, 1889
The largest of the three American orders is Didelphimorphia, which is represented by the family Didelphidae Gray, 1821, whose species are widely distributed throughout the continent
In the species with 2n=14, we observed a very similar structure among the autosomes. These karyotypes include six autosome pairs (Fig. 2), three large submetacentric pairs, one metacentric pair and two small pairs that varied in morphology in the different species, resulting in differences in the chromosomal formulas and fundamental numbers (FNa)
Summary
In the Americas, subclass Metatheria Huxley, 1880 is represented by the three marsupial orders: Didelphimorphia Gill, 1872, Paucituberculata Ameghino, 1894 and Microbiotheria Ameghino, 1889. The largest of the three American orders is Didelphimorphia, which is represented by the family Didelphidae Gray, 1821, whose species are widely distributed throughout the continent. Didelphidae is the only marsupial group present in Brazil. Together with rodents, they make up an important part of the mammalian fauna of the Amazon region (Voss and Jansa 2009, Wilson and Reeder 2011). 14 genera and 39 species are recorded in the Amazon basin. Moderate in terms of species richness, didelphids are abundant in the region (Brandão et al 2015)
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