Diferenciacao cromossomica em Kerodon rupestris (Rodentia: Caviidae) da regiao semiarida brasileira.
Kerodon rupestris (Wied, 1820) is the most specialized species among caviid rodents and it is considered endemic to the extensive rocky outcrops that occur in the Caatinga semi-arid region in Brazil, from Piaui State to northern Minas Gerais State (Lacher, 1979, 1981; Alho, 1982; Mares and Ojeda, 1982; Oliveira et al., 2003; Lessa and Pessoa, 2005). Despite its wide distribution and habitat specialization, little effort has been made to examine karyological variation in this species (Maia and Hulak, 1978; Maia, 1984).
Maia (1984) analyzed karyological variation in the three genera of Brazilian caviids, Cavia (Pallas, 1766) Galea (Meyen, 1833) and Kerodon (Cuvier, 1825), and showed that 80% of their chromosomal complement was composed of biarmed chromosomes and considerable karyological symmetry occurred in the genera. In the same study she gave the diploid and fundamental numbers for K. rupestris from Pernambuco as 2n = 52 and FN = 92. C-band results showed that all constitutive heterochromatin was confined to the X chromosome, differing from the pattern observed in Cavia and Galea. No study focusing on karyological variability in K. rupestris has been published since then.
Lessa et al. (2005), studying morphometric characters in K. rupestris, found a clinal increase in cranial size from north to south. The population from Botumirim was completely discriminated in morphometric multivariate space from the other population in the northeastern part of the species range. These authors also suggested that this cranial variation pattern was associated with the distribution of rocky outcrops. Moojen et al. (1997) suggested this association when describing Kerodon acrobata, a new species within this genus.
Central to the understanding of variability in K. rupestris is the inclusion of samples from throughout its range and from places as near as possible to the type locality of the species. The aim of this study is therefore to describe karyological variation in samples from the northern, central and southern parts of the species range, the last area being within 100 km of the type locality, and to compare it with information previously described for a population sample from Pernambuco. A further objective was then to test whether karyological variation corroborated the found morphometric cranial pattern for the species.
We karyotyped one specimen of K. rupestris collected in Itapaje (CE) (03[degrees]41'S-39[degrees]34'W), Ceara State (CE) in November 2003. A second karyotyped sample consisted of two specimens collected in Iraquara (BA), (12[degrees]15'S-41[degrees]36'W), in April 2004. The third sample was composed of six specimens collected in Botumirim (MG) (16[degrees]52'S-43[degrees]01'W), between June 2001 and July 2002 (Fig. 1).
The skins and skulls of the karyotyped specimens are deposited in the mammal collection of Museu Nacional (MN) in Rio de Janeiro: one female from Itapaje (CE), (MN 67469); two males from Iraquara (BA), (MN 68092 and MN 68094); two males and two females from Botumirim (MG), (MN 65151, MN 67465, MN 67466, MN 67467).
Cytogenetic analyses were based on mitotic metaphase chromosomes from bone marrow, following Ford and Harmerton (1956) with modifications. Chromosomes were stained with Giemsa and classified following Levan et al. (1964). Metacentric, submetacentric and subtelocentric chromosomes are considered biarmed and acrocentric ones uniarmed. C-bands were showed by techniques described by Sumner (1972).
[FIGURE 1 OMITTED]
The karyotype of the northern population specimen from Itapaje (MN 67469), had a diploid number (2n) of 52 and a fundamental number (FN) of 92, and was comprised of 21 pairs of metacentric/submetacentric chromosomes, and four pairs of acrocentrics. The X chromosome is a large metacentric, the largest of the karyotype, and the Y is a medium-sized acrocentric (Fig. 2a). The distribution of constitutive heterochromatin (C-banding) in this specimen showed pericentromeric bands in all autosomes. The X chromosome was entirely heterochromatic (with stronger marks in interstitial regions) whereas the Y chromosome was totally hetero chromatic (Fig. 3a).
The karyotype of specimens from the central population, Iraquara (MN 68092 and MN 68094) and distribution of constitutive heterochromatin (C-banding; Fig. 3b), was identical to that of the Itapaje specimen (Fig. 2b).
The karyotype of specimens from Botumirim (MN 65150, MN 65151, MN 67465, MN 67466, and MN 67467), the southern population sample, had 2n = 52 and NF = 94, and was comprised of 22 pairs of metacentric/ submetacentric chromosomes, and three pairs of acrocentrics. As in the Itapaje and Iraquara karyotypes, the X chromosome was a large metacentric, the largest of the complement, and Y was a medium-size acrocentric (Fig. 2c). The distribution of constitutive heterochromatin (C-banding) showed pericentromeric bands in all autosomes. The X chromosome was entirely heterochromatic (with stronger marks in interstitial regions) whereas the Y chromosome was totally heterochromatic, as in the other two populations (Fig. 3c). For all populations, NOR sites were found in the short arms of chromosome pairs 10 and 11.
Karyological examination of these specimens and Maia's (1984) results revealed that the karyotype of the southern population (Botumirim) has conspicuous differences when compared with northern and central populations. Diploid and fundamental numbers described here (2n = 52 and FN = 92) for K. rupestris from Itapaje (north) and Iraquara (central) corroborate Maia's (1984) results from the Pernambuco population, although our results for distribution of heterochromatin differ from Maia's. Maia's study revealed that all heterochromatin was confined to the X chromosome in the Pernambuco population; in contrast, in all samples used here the distribution of constitutive heterochromatin (C-banding) showed pericentromeric bands in all autosomes. The X chromosome was entirely heterochromatic (with stronger marks in interstitial regions) whereas the Y chromosome was totally heterochromatic. In all samples, NOR sites were found in the short arms in metacentric chromosomes 10 and 11. That seems to be constant in all populations of K. rupestris.
Species within Caviinae have a high diploid number (2n = 64) and only three of them differ from this number: Galea musteloides (Meyen, 1833) (2n = 68), K. rupestris (2n = 52) and Cavia aff. C. magna (Ximenez, 1980) (2n = 62) (George and Weir, 1972; Maia, 1984; Gava et al., 1998). Comparisons and more details in diploid and fundamental numbers are shown in Table 1.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
A difference in FN was also observed within K. rupestris: between northern and central population samples (NF = 92) and southern population sample (NF = 94). This difference can be explained by a pericentric inversion in one pair of autosomes. These differences in FN found in other caviomorph rodents have led authors to suggest that a complex of species may be involved. For example there are a number of taxa within Echimyidae which show this pattern. Species in the genus Trinomys have the same 2n but different FNs (Correa et al., 2005). The same occurs within species of Proechimys collected in Brazilian Amazon and Cerrado regions (Weksler et al., 2001) and Isothrix (Vie et al., 1996).
In the case of K. rupestris, the difference in FN found in the southern population sample is congruent to the variability described in cranial morphometric characters for this population (Lessa et al., 2005). These results indicate that southern population sample has probably undergone processes of differentiation in relation to the other two populations. Future studies on other kinds of chromosomal banding and on molecular data will elucidate the level of divergence among these populations. It is noteworthy that the southern population sample is only 100 km from the type locality reported by Wied (1820) as Rio Belmonte, on the border between northern Minas Gerais State and southern Bahia State. We suggest that the karyotype of the K. rupestris should be taken to be 2n = 52, FN = 94/92 as this group is located in the type locality region.
Recibido: 2 octubre 2012. Aceptado: 15 mayo 2013. Editor Asociado: UFJ Pardinas
Acknowledgments. The authors would like to thank Danilo Souza, Marcia Gomide, Maria Somalia Vianna for support and help in fieldwork in Ceara State, as well as the administration of Centro de Recursos Ambientais in State of Bahia represented by Aloisio Cardoso. To Joelma de Lourdes Silva to the material collected in Botumirim, Minas Gerais State. We thank J. A. Oliveira for permission to study specimens and for their hospitality during the visits in Museu Nacional (UFRJ). C. J. Tribe kindly revised an English version of the manuscript. To professors of Citogenetic Laboratory and Vegetal Microscopy (Universidade Federal de Vicosa) for utilization of equipment and some photography used in this study. Work by the authors has been funded by grants from CAPES, Universidade Federal do Rio de Janeiro, and Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ-E-26/170.547/99). L. M. Pessoa has been partially supported by a fellowship from Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq- 302058/2004-4). Licenses for collecting were provided by Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renovaveis (IBAMA).
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Gisele Lessa (1), Margaret M. O. Correa (2), Leila M. Pessoa (2), and Ighor A. Zappes (1)
(1) Museu de Zoologia Joao Moojen, Universidade Federal de Vicosa, 36570-000 Vicosa, Minas Gerais, Brazil [Correspondence: Gisele Lessa <email@example.com>].
(2) Departamento de Zoologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Table 1 Summary of karyotype data of the subfamily Caviinae with data of present study. Acronyms read as follows: 2n = diploid number; FN = fundamental number. Modified from George and Weir (1974), and Kasahara and Yonenaga-Yassuda (1984). Species n FN X Y Reference Cavia aperea 64 118 Small Micro George et al. (1972) C. aperea 64 116 -- -- Kasahara (1981), Mariano et al. (1983), Maia (1984), Maia and Hulak (1974) Cavia 64 118 Small -- Cohen and Pinsk porcellus (1966) Cavia aff. 62 112 Large Large Maia and Hulak C. magna (1978) Cavia 64 104-108 Medium Medium Dunnum and tschudii Salazar-Bravo (2006) Galea 68 130 Medium Small George et al. musteloides (1972) Galea spixii 64 118 Small Small Gava et al. (1998) Kerodon 52 92 Medium Medium Maia (1984) rupestris [Pernambuco] K. rupestris 52 92 Medium Medium Present study [Itapaje; Iraquara] K. rupestris 52 94 Medium Medium Present study [Botumirim]
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|Author:||Lessa, Gisele; Correa, Margaret M.O.; Pessoa, Leila M.; Zappes, Ighor A.|
|Date:||Dec 1, 2013|
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