Cariotipo de un marsupial suramericano raro, zarigueya de cola peluda, del genero Glironia (Didelphidae, Didelphimorphia).
The karyotypes of didelphid marsupials are characterized by a relatively low number of chromosomes, with diploid numbers of 2n = 22 in the larger species of opossums (Didelphis, Philander, Chironectes and Lutreolina) and one species of "mouse-opossum" Tlacuatzin canescens (Engstrom and Gardner, 1988; Zarza et al., 2003), 2n = 18 in the shorttailed opossums of the genus Monodelphis and 2n = 14 (by far the most common diploid number) in Metachirus, Caluromys and five genera of small-bodied "mouse opos sums" (Gracilinanus, Marmosa, Marmosops, Micoureus and Thylamys; Carvalho et al., 2002, and references cited therein).
The bushy-tailed opossum Glironia venusta (Didelphidae, Didelphimorphia) is considered one of the rarest South American marsupials and is listed as "Vulnerable" in the 2006 IUCN Red List of Threatened Species (IUCN, 2006). Very little is known about its habits and natural history. It is considered to be arboreal and has a highly developed hallux (Marshall, 1978; Emmons and Feer, 1997). In addition to its abilities for arboreal locomotion, the postcranial morphology of Glironia venusta also indicates some capacities for terrestrial habits (Flores and Diaz, 2009). Indeed, G. venusta has also been observed to use the lower strata of the forest (MNF da Silva, pers. obs.), has been captured with live traps in the forest understory (Diaz and Willig, 2004; Santos-Filho et al., 2007) and has also been captured in pitfall traps on the ground (Bernarde and Rocha, 2003).
Known originally from Bolivia, Ecuador and Peru (Marshall, 1978; Diaz and Willig, 2004), its occurrence in Brazil has now been documented at nine widely separated localities in the Amazon and Paraguay basins (da Silva and Langguth, 1989; Patton et al., 1996; Nogueira et al., 1999; Bernarde and Rocha, 2003; Santos-Filho et al., 2007; Calzada et al., 2008, Rossi et al., 2010). Voucher specimens from Brazil are deposited in the mammal collection at the National Institute for Amazonian Research (INPA 699, 2570, 4577, 5237), in the Museu de Zoologia da Universidade de Sao Paulo (MZUSP 34664), and in the mammal collection of the Universidade Federal de Mato Grosso (UFMT 696) (Santos-Filho et al., 2007; Rossi et al., 2010). The sites in Rondonia (Bernarde and Rocha, 2003), Manaus (Calzada et al., 2008) and in southeastern Para (Rossi et al., 2010) do not have voucher specimen. According to Barkley (2007), the total number of known specimens of G. venusta is under 25.
In this report, the description of the karyotype of the bushy-tailed opossum Glironia venusta is presented for the first time.
The single specimen available for cytogenetic analyses (INPA 4577; skull and body in fluid) represents a young female from Teotonio, on the right bank of the Rio Madeira, 19 km SW of Porto Velho, Rondonia, Brazil (8[degrees]52'27"S 64[degrees]0'28" W).
A suspension of mitotic metaphase bonemarrow cells was obtained in the field from this single available specimen employing a slightly modified version of Patton's (1967) colchicinehypotonic salt and Carnoy's fixative protocol using a hand-operated centrifuge. Air-dried slides were subsequently prepared and stained with Wright's stain; a total of 30 cells were examined and five of those were photographed under oil immersion using bright-field optics. Chromosomes were sorted by decreasing size and classified according to Levan et al. (1964). C-banding (in a total of 10 cells) and silver staining of the nucleolar organizer regions (Ag-NORs--in 20 cells) were performed following protocols described by Sumner (1972) and Howell and Black (1980), respectively.
The diploid number of chromosomes in the female bushy-tailed opossum Glironia venusta is 18. The karyotype (Fig. 1) consists of 2 large pairs of metacentric/submetacentric (pairs 1 and 2), 1 pair of subtelocentric (pair 5) and 5 pairs of acrocentric autosomes (pairs 3, 4 and 6 to 9). We presume that the smallest pair of acrocentrics represents the X chromosomes, as this pattern has been found for many didelphid species (Palma and Yates, 1996; Svartman and Vianna-Morgante, 1999, 2003; Carvalho et al., 2002). The number of autosomal chromosomal arms (FN) is 22.
Silver-staining analysis revealed the activity of nucleolar organizer regions (NORs) on the short arms of both acrocentric chromosomes of autosomal pair number 6; the presumptive sex chromosomes did not show NOR activity (Fig. 2A and B).
Constitutive heterochromatin was not observed in the autosomes of G. venusta. C-bands are restricted to sex chromosomes where they are revealed as diffusely stained blocks in the pericentromeric region of both presumptive X chromosomes (Fig. 2C; Table 1).
G-banding and treatment with CMA3 were performed but we did not yield reliable results. These trials were probably hampered by the high condensation of the chromosomes and by limited suitable material in the cell suspensions. When additional materials become available, a new trial of both sets of analyses should be performed.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
In general, the distribution and expression of NORs in marsupials has been reported on one or more autosomal pairs, alone or in association with the sex chromosomes; in the latter case, NORs are either restricted to the X chromosome or they are found on both X and Y chromosomes (Svartman and ViannaMorgante, 2003). According to Svartman and Vianna-Morgante (1999, 2003), pair 7 in species with 2n = 22, corresponds to pair 5 in species with 2n = 18 and pair 6 in species with 2n = 14 and these homeologous pairs are NOR-bearing chromosomes. Although pairs 5 and 6 are of similar size in the Glironia karyotype, pair 5 is approximately 9.0% larger then the NOR-bearing pair 6. This pattern contrasts to the pattern found in the 2n = 18 karyotype but fits with that of the 2n = 14 species, including its presence on the short arms, reinforcing the idea that the presence of NORs on this chromosome is a conserved condition in Didelphidae.
The only other didelphid genus previously reported to have a diploid number of 18 is Monodelphis. The fundamental number among species of Monodelphis varies considerably from 22 to 32 (Carvalho et al., 2002). Among these karyotypes (e.g., by Palma and Yates, 1996; Carvalho et al., 2002; Svartman and Vianna-Morgante, 2003), that of M. glirina from Bolivia (reported as M. brevicaudata; see Voss et al., 2001) by Palma and Yates (1996) is very similar to that of Glironia, despite differences between our respective classifications of chromosomes (compare op. cit.: Figure 4 and Table 1 with our Fig. 1 and the karyotypic description above). Additional work such as chromosome banding and in-situ hybridization may determine the degree of similarity between these two karyotypes.
The similarity in diploid number and karyotype between these two genera is somewhat surprising since Glironia is often classified with Caluromys (2n=14) and Caluromysiops (diploid number unknown) in a distinct subfamily or family (Hershkovitz, 1992; Kirsch et al., 1995; Kirsch and Palma, 1995; McKenna and Bell, 1997; Gardner, 2005). However, the phylogenetic work of Voss and Jansa (2009), based on cladistic analyses of both molecular sequences and morphological characters, supports an alternative hypothesis, namely that Glironia is sister to all other opossums and is not the sister group of a Caluromys+Caluromysiops clade. The separation of Glironia from Caluromys and Caluromysiops is also reinforced by the distinctiveness of the skeletal morphology of Glironia when compared to these two genera (Flores and Diaz, 2009). If Glironia is sister to all other opossums, then the 2n=18 karyotype could either be ancestral for didelphimorphs, or the similarity in diploid number of Glironia and Monodelphis resulted from convergent evolution. The validity of these hypotheses can be examined in future analyses of cytogenetic and molecular markers once such are available.
Recibido 25 enero 2010. Aceptado 17 marzo 2011. Editor asociado: E Lessa
Acknowledgements. The specimen used for this study was obtained during a consulting project funded by Furnas Centrais Eletricas S.A. We are grateful to Dr. Antonia Franco, project coordinator, and to the project field biologists Barbara A. Costa, Carla G. Bantel, Manoel dos Santos Filho, Dionei Jose da Silva and Carlos Leonardo G. Vieira who collected the Glironia specimen and prepared the cell suspension in the field. We thank Drs. James L. Patton and Robert S. Voss for reviewing the manuscript and Dr. Marta Svartman for helpful criticisms, but any errors of fact or interpretation are our responsibility. We also thank Dr. Eliana Feldberg for providing support and permission to work on her laboratory at INPA. Thanks also to Glenn H. Shepard Jr for editorial assistance on the final draft and figures. MNFS research is partly funded by CNPq and FAPEAM, Brazil.
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Cleiton Fantin (1) and Maria Nazareth F. da Silva (2)
(1) Universidade do Estado do Amazonas, Departamento de Biologia. Av. Djalma Batista, 2470, 69050010, Manaus, AM, Brazil. (2) Instituto Nacional de Pesquisas da Amazonia, Colecao de Mamiferos, Caixa Postal 478, Manaus-AM, CEP 69060-000, Brazil. [Correspondence: Maria Nazareth F. da Silva <email@example.com>]
Table 1 Karyotype and C-banding patterns of didelphid marsupials. Species 2n FN C-banding positive Autossomes Caluromys 14 22 Pericentromeric lanatus in all Caluromys 14 20 Pericentromeric philander in all Didelphis 22 20 Centromeric in albiventris all Distal portion Didelphis 22 20 of long arms of marsupialis some chromosomes Glironia 18 22 venusta Gracilinanus 14 24 Pericentromeric microtarsus in all Gracilinanus 14 24 Pericentromeric emiliae in all Marmosa 14 20 Centromeric cinerea in all Marmosa 14 20 Pericentromeric murina in all Marmosops 14 24 Pericentromeric incanus in all Metachirus 14 20 Pericentromeric in nudicaudatus pairs 5 and 6 Large pericen-tromeric blocks Micoureus 14 20 pairs1-4; blocks in demerarae distal long arms of 5 and 6 Monodelphis 18 22 americana Monodelphis 18 30 Pericentromeric brevicaudata in all Monodelphis 18 32 Pericentromeric dimidiata in all Monodelphis 18 20 Pericentromeric domestica in all Monodelphis 18 30 Pericentromeric kunsi in all Philander 22 20 Pericentromeric opossum in all Thylamys 14 20 Pericentromeric elegans in all Species C-banding positive Reference X Y Caluromys Pericentromeric Rofe and Hayman, lanatus 1985 Caluromys Pericentromeric Total Souza et al., philander and distal regions 1990. in the long arms Didelphis Long arms Total Casartelli et al., albiventris 1986 Didelphis Pericentromeric Total Svartman and Vianna marsupialis -Morgante, 1999 Glironia Pericentromeric This article venusta Gracilinanus Pericentromeric Carvalho et al., microtarsus 2002 Gracilinanus Pericentromeric Carvalho et al., emiliae 2002 Marmosa Long arms Total Casartelli et al., cinerea 1986 Marmosa Pericentromeric Souza et al., murina 1990. Marmosops Pericentromeric Svartman and Vianna incanus and distal blocks -Morgante, 1999 in the arms Metachirus Pericentromeric Total Svartman and Vianna nudicaudatus -Morgante, 1999 Micoureus Pericentromeric Total Svartman and Vianna demerarae and distal regions -Morgante, 1999 of long arms Monodelphis Pericentromeric Total Pagnozzi et al., americana 2002 Monodelphis Pericentromeric Total Carvalho et al., brevicaudata 2002 Monodelphis Pericentromeric Total Carvalho et al., dimidiata 2002 Monodelphis Pericentromeric Total Merry et al, 1983; domestica Svartman and Vianna -Morgante, 1999 Monodelphis Pericentromeric Total Carvalho et al., kunsi 2002 Philander Pericentromeric and Svartman and Vianna opossum lag blocks in -Morgante, 1999 long arm Thylamys Pericentromeric Spotorno et al., elegans 1997
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|Author:||Fantin, Cleiton; da Silva, Maria Nazareth F.|
|Date:||Jun 1, 2010|
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