Karyotypic analyses and morphological comments on the endemic and endangered Brazilian painted tree rat Callistomys pictus (Rodentia, Echimyidae) Karen Ventura 1 , Gilson Evaristo Iack Ximenes 2 , Renata Pardini 3 , Marcos A. Nóbrega de Sousa 4 , Yatiyo Yonenaga-Yassuda 1 and Maria José de J. Silva 5 1 Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil. 2 Departamento de Ciências Biológicas, Universidade Estadual de Santa Cruz, Ilhéus, BA, Brazil. 3 Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil. 4 Centro de Ciências Biológicas e Sociais Aplicadas, Universidade Estadual da Paraíba, João Pessoa, PB, Brazil. 5 Laboratório Especial de Ecologia e Evolução, Instituto Butantan, São Paulo, SP, Brazil. Abstract The genus Callistomys belongs to the rodent family Echimyidae, subfamily Echimyinae, and its only living represen- tative is Callistomys pictus, a rare and vulnerable endemic species of the state of Bahia, Brazil. Callistomys has been previously classified as Nelomys, Loncheres, Isothrix and Echimys. In this paper we present the karyotype of Callistomys pictus, including CBG and GTG-banding patterns and silver staining of the nucleolus organizer regions (Ag-NORs). Comments on Callistomys pictus morphological traits and a compilation of Echimyinae chromosomal data are also included. Our analyses revealed that Callistomys can be recognized both by its distintinctive morphol- ogy and by its karyotype. Key words: Callistomys, karyotype, banding patterns, Echimyinae. Received: September 28, 2007; Accepted: March 17, 2008. The Neotropical spiny rats of the family Echimyidae comprise approximately 85 recognized living species grouped in 21 genera (modified from McKenna and Bell, 1997; Woods and Kilpatrick, 2005; Emmons, 2005; Iack- Ximenes et al., 2005). Echimyids have a wide distribution, ranging from Southern Paraguay to Southern Nicaragua (Anderson and Jones, 1967; Honacki et al., 1982; Harten- berger, 1985). They are the most diverse of all living hystri- cognath rodents and the evolutionary relationships among genera are still unclear due to the paucity of data regarding their ecology, diversity and systematics (Leite and Patton, 2002; Woods and Kilpatrick, 2005). Woods and Kilpatrick (2005) recognized four Echi- myidae subfamilies: (1) the extinct Heteropsomyinae, en- demic to West India; (2) Dactylomyinae, including the arboreal bamboo rats from the genera Dactylomys, Kannabateomys and Olallamys; (3) Echimyinae, including the arboreal genera Callistomys, Diplomys, Echimys, Phyllomys, Isothrix and Makalata; and (4) Eumysopinae, including the semi-fossorial, arboreal and terrestrial genera Carterodon, Clyomys, Euryzygomatomys, Lonchothrix, Mesomys, Hoplomys, Proechimys, Trinomys and Thrichomys. Since then, several new genera of Echimyinae have been erected: Pattonomys to include Nelomys semivillosus Geoffroy, 1838 and allied species, Santamartamys to include Isothrix rufodorsalis Allen, 1899 (Emmons, 2005) and Toromys to include Loncheres grandis Wagner 1845 (Iack-Ximenes et al., 2005). Karyotypes of Echimyinae are known only for Pattonomys semivillosus and for some species of Phyllomys, Makalata and Isothrix and their chromosome numbers ranged from 2n = 22 in Isothrix pagurus to 2n = 96 in Phyllomys medius (Table 1). The painted tree rat or cocoa rat Callistomys pictus (Pictet, 1843) is a soft-furred echimyid found in the coast of the state of Bahia, Northeastern Brazil. It was originally in- cluded in the genus Nelomys as a junior synonym of Echimys. It was afterwards alternatively classified as Genetics and Molecular Biology, 31, 3, 697-703 (2008) Copyright © 2008, Sociedade Brasileira de Genética. Printed in Brazil www.sbg.org.br Send correspondence to Maria José de Jesus Silva. Laboratório Especial de Ecologia e Evolução, Instituto Butantan, Av. Dr. Vital Brazil 1500, 05503-900 São Paulo, SP, Brazil. E-mail: mariajo@ butantan.gov.br or mariajo@usp.br. Short Communication