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Caryologia
International Journal of Cytology, Cytosystematics and Cytogenetics
ISSN: 0008-7114 (Print) 2165-5391 (Online) Journal homepage: https://www.tandfonline.com/loi/tcar20
Chromosome Studies on the Silky Anteater
Cyclopes Didactylus L. (Myrmec Ophagidae:
Xenarthra, Edentata)
Wilham Jorge, Robin C. Best & Ralph M. Wetzel
To cite this article: Wilham Jorge, Robin C. Best & Ralph M. Wetzel (1985) Chromosome Studies on the Silky Anteater Cyclopes�Didactylus L. (Myrmec Ophagidae: Xenarthra, Edentata), Caryologia, 38:3-4, 325-329, DOI: 10.1080/00087114.1985.10797756
To link to this article: https://doi.org/10.1080/00087114.1985.10797756
Published online: 31 Jan 2014.
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CHROMOSOME STUDIES ON THE SILKY ANTEATER
CYCLOPES DIDACTYL US
L.
(MYRMECOPHAGIDAE: XENARTHRA, EDENTATA)
WILHAM JORGE, ROBIN C. BEST * and RALPH M. WETZEL **
Department of Genetics, UNESP, Campus of Botucatu, 18600 Botucatu, Sao Paulo, Brazil; * Institute Nacional de Pesquisas da Amazonia (INPA), 69000 Manaus, Amazonia, Brazil; **Biological Sciences Group, University of Connecticut, Storrs, Connecticut 06268, and Florida State Museum, Univ. Florida, Gainesville, FL 32611, USA.
SUMMARY- The karyotype of the silky anteater Cyclopes didactylus, the smallest of
the anteaters is described. A notable difference in karyotypes exists between C. didactylus (2n = 64) and the other species of the family Myrmecophagidae. Both fusion/fission as well as other mechanisms are probably involved in the reduction of the chromosome number of 64 chromosome in Cyclopes to 60 and 54 in Tamandua and Myrmecophaga, respectively.
INTRODUCTION
The xenarthrans or edentates are by definition toothless, however in actual fact only the anteaters are characterized by this description. Armadillos have molariform teeth and the sloths present both canines and molars (Choloe-pus) or only molars (Brady(Choloe-pus).
Mammalian cytogenetics has made great progress in recent years in general, yet the published works on xenarthrans are contained in a handful of papers. In 1969, the karyotypes of five species of armadillos were published by
BENIRSCHKE et al. (1969). More recently, JoRGE (1982) and JoRGE et al. (1985)
present the karyotypes of 13 species of edentates of the families Bradypodidae (the three-toed sloths), Megalonychidae (two-toed sloths), Dasypodidae (arma-dillos) and Myrmecophagidae (anteaters). Taxonomy follows that of WETZEL
(1982, 1985).
The difficulty of capturing and maintaining anteaters in captivity is the primary reason for the lack of studies of these species. Hsu (1965) described the karyotypes of the two larger species of anteaters, the tamandua (Tamandua tetradactyla) and the giant anteater (Myrmecophaga tridactyla). JoRGE et al.
(1977) confirmed karyotypically the conclusions of WETZEL (1975) that T.
326 JORGE, BEST and WETZEL has been reduced to synonomy. The karyotype of the giant anteater 2n = 60, is quite distinct from the one of Tamandua (2n =54). In the present study, the karyotype of the silk anteater, Cyclopes didactylus, is presented and discussed in relation to the reduction in chromosome number in the Myrmecophagidae.
MATERIAL AND METHODS
A female Cyclopes didactylus was obtained in the region of Lago Amana, Rio
Jupura, Amazonas State, Brazil (2°46'S, 64°39'W) on the 8 August, 1982. The skin and skull of this specimen are preserved in the collection of the Aquatic Mammal Department N° 20 RMW of the «lnstituto Nacional de Pesquisas da Amazonia», Brazil. The animal was inoculated with 1 ~g/g body weight of colchicine and sacrificed 2h later using ether. A suspension of cells was made by mixing the bone marrow in 5 ml 0.075M KCI. Hypotonic treatment was carried out with 0.075M KCl for 20 min and stained with Giemsa. A total of 40 metaphases were analysed and 6 karyotypes were mounted.
RESULTS
The modal number of chromosome for Cyclopes was 64 as shown in Fig. 1. As the individual analysed was a female the sexual chromosomes could not be identified. The chromosomes were divided in two groups according to centro-meric position and decreasing size, one groups of 19 pairs and the other containing 13 pairs of chromosomes. The sex chromosomes were not identifi-able.
DISCUSSION
Cytogenetic analysis has shown that there are three distinct karyotypes associated with each of the genera of Myrmecophagidae. This permits the assumption that there are only three distinct karyotypic patterns, perfectly identifiable with the genera Myrmecophaga, Tamandua and Cyclopes.
Some compilers (CABRERA 1957; MoRRIS 1965) considered the genus Tamandua to have two species in South America, while VIEIRA (1955) only one.
WETZEL (1975) found the genus Tamandua to have a northern species in Central America and NWSouth America (T. mexicana) and a southern species confined to South America east of the Andes (T. tetradactyla), including T. longicaudata within the latter species.
Cytogenetic analysis (JoRGE et al. 1977) has shown that Tamandua longi-caudata and T. tetradactyla have the same karyotype (2n = 54). In contrast, Myrmecophaga tridactyla (2n
=
60) and Cyclopes didactylus (2n=
64) differFig. 1. - Karyotype of a female specimen of Cyclopes didactylus (2n = 64). The karyotype is composed of two groups of chromosomes according to centromeric position and decreasing size. The sex chromosomes are not identifiable (pair n. 3?).
markedly in chromosome complement. The species in the genus Tamandua do not exhibit acrocentric chromosomes and have similar karyotypes, a fact that favors the idea of systematic affinity between these two species despite their striking geographical gradient in body size weight and pelage. According to Hsu (1965), M. tridactyla has 2n = 60 chromosomes, with six acrotelocentric pairs. On the other hand, Cyclopes didactylus (Fig. 1), with 2n = 64 chromo-somes, has 13 acrotelocentric pairs.
On the basis of the model presented by HoLMQUIST and DANCIS (1980)
Robertsonian translocation between two acrotelocentric chromosomes leads to the formation of a metacentric through reversible processes and according to three different possibilities: a) reciprocal translocation between two acrocen-trics with the formation of a metacentric and a small centric fragment; b)
328 JORGE, BEST and WETZEL TABLE 1 - Comparison of the karyotypes of four species of the genera «Tamandua», «Myrmecophaga» and
«Cyclopes».
Acrotelo-
Submeta-Species 2n centric centric X y FN Reference pairs pairs
Tamandua tetradactyla 54 27 submet. submet. 108 Hsu (1965).
Tamandua longicaudata 54 27 submet. ? 108 JoRGE et al. (1977).
Myrmecophaga tridactyla 60 6 24 metac. subtel. 108 Hsu (1965).
Cyclopes didactylus 64 13 19 ? ? 100 Present paper.
reversible fusion-fission between two telocentrics, with the production of a metacentric; and c) reversible fusion-fission of two acrocentric with the pro-duction of a metacentric with two centromeres. The cytologic transformation of the karyotype in the family Myrmecophagidae can be interpreted as a simple fusion - fission mechanism in the genera Tamandua and Myrmecophaga. No alterations in arm number (FN = 108) occur in either genus (Table 1), and the increase in the number of submetacentric pairs corresponds to a decrease in the number of acrotelocentric chromosomes. This process consists of the joining of two acrocentric or telocentric chromosomes to form a meta-submetacentric (fusion), or the dissociation of a submetacentric (fission).
In Cyclopes, the increase in diploid number does not correspond to a decrease in the supposed meta-submetacentric number (pairs 1-19) and in increase in acrocentric number (pairs 20-32). Furthermore, the arm number is lower (FN = 100), demonstrating that other mechanisms in addition to fusion-fission must be involved, such as inversions, translocations, shift, etc.
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