Chromosomes of Alouatta seniculus (Platyrrhini, primates) from French Guiana.

Karyotypes of 42 specimens of Alouatta seniculus from French Guiana were analyzed by Gand/or R-banding, C-banding, and NORs Ag-staining techniques. The samples were collected during a rescue operation performed at the Petit Saut dam site. All studied specimens but one possess diploid chromosome numbers ranging from 47 to 49, this variation being due to the presence of one to three supernumerary or B-chromosomes (B's). Males exhibit a Y;autosome translocation involving the short arm of an individual biarmed autosome, which results in the following sex chromosome systems: X,X2Y,Y2 in males and X^XjPO, in females. Different degrees of chromosome heteromorphism were observed in pairs 9, 12, 14, 19, 21, and 22 related with variations in the amount of constitutive heterochromatin. Of special interest is the heteromorphism for pair 7 (X2) observed in the females, whereas only one of two variants was constantly found in males. Comparisons with other A. seniculus chromosomal data reported in the literature indicate that Red Howlers from French Guiana resemble very closely, from a taxonomic point of view, A. s. macconnelliUom the Jari River (Brazil). These data could be used to estimate biodiversity and to reassess taxonomic criteria in this group. Howler Monkeys are among the largest New World monkeys. Until now they were considered to belong to the Cebidae family, but new molecular data (globin gene sequences) indicate that they could be included in the family Atelidae (Schneider et al. 1993). There are eight species in the genus Alouatta (Groves 1994). They are arboreal, diurnal forest dwellers characterized by their coloration (yellow, red, or black) and their remarkable vocalizations. Few allozymic data are available on the natural genetic variation of Alouatta (Lima et al. 1990; Schneider et al. 1991). Understanding the chromosome evolution in the family Cebidae is complicated because of the significant karyological differences observed between specimens presently considered to belong to the same species (Moore et al. 1990; Pieczarka et al. 1993). A seniculus is the most extensively spread of all howler monkeys found in Colombia, Venezuela, Guianas, eastern Ecuador, northeastern Peru, Amazonian Brazil, and Bolivia (Groves 1994; Nowak 1991). Morphometric and biogeographical data led Hill (1960) to propose that A. seniculus comprises nine different subspecies. However, this taxonomic arrangement is controversial, because Cabrera (1958) has recognized four subspecies, and Napier and Napier (1967) five different subspecies. For this reason, genetic characterization of specimens captured in known geographic regions is of vital importance to estimate more accurately biodiversity and to reassess taxonomic criteria. Chromosome studies in A seniculus seniculus from Colombia (Yunls et al. 1976), A s. macconnelli from the northern Amazonas, Jari river (Lima et al. 1990), A s. stramineus from the Uatama river (Lima and Seuanez 1991), and A s. arctoidea from Venezuela (Stanyon et al. 1995) have shown differences in their diploid chromosome number and in their type of sex-chromosome system. The specimens studied by Yunis et al. (1976) presented a difference in diploid number and a XX/XY sex chromosome system when compared to specimens from Jari and Uatama rivers. However, these latter two shared the same diploid