The chromosomes of the Didelphidae (Marsupialia) and their evolutionary significance |
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| Authors: | OSVALDO A. REIG F.L.S. ALFRED L. GARDNER NESTOR O. BIANCHI JAMES L. PATTON |
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| Affiliation: | Departamento de Estudios Ambientales, Division de Ciencias Biólogicas, Universidad Simon Bolivar, Apartado 80,659, Caracas 108, Venezuela;National Fish and Wildlife Laboratory, Fish and Wildlife Service, National Museum of Natural History, Washington, D.C., U.S.A. 20560;Instituto Multidisciplinario de Biologia Celular (IMBICE), Calle 526 entre 10 y 11, La Plata, Argentina;Museum of Vertebrate Zoology, University of California, Berkeley, California, U.S.A. 94720 |
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| Abstract: | One hundred and seventy-seven specimens of American didelphids, representing 9 genera and 22 species have been studied for their chromosomal constitution. Didelphids are very conservative in chromosomal complements. All of the studied species can be sorted into one of three kinds of karyotypes: 2 n = 14 (three species of Didelphis, one of Lutreolina, two of Philander, and one of Chironectes) , 2 n = 14 (eight species of Marmosa, one of Metachirus, three of Caluromys, and one of Dromiciops), and 2 n = 18 (three species of Monodelphis). These karyotypes are stable, showing only minor variations within each basic pattern. It is concluded that chromosomals evolution in the Didelphidae proceededs from low numbers to higher numbers by a process of centromeric fissioning complemented by some pericentric inversions and/or translocations. The pattern of karyotypic stability is consistent with bradytely at the organismic level of evolution. This is explained by a low rate of regulatory genetic evolution promoted by epistatic selection favouring the retention of chromosomal arrangements highly advantageous for overall adaptation. |
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