Cytogenetic study of the giant otter Pteronura brasiliensis Zimmermann 1780 (Carnivora, Mustelidae, Lutrinae)

Abstract

The giant otter, Pteronura brasiliensis Zimmermann 1780 (Carnivora, Mustelidae, Lutrinae), was widely distributed in South America but stable populations are now only found in the Pantanal and Amazon regions and the species is classified as endangered. There is only one recognized species of giant otter, although two subspecies of doubtful value have also been cited in the literature. We present the first karyotype of four captive P. brasiliensis specimens, all of which posses 2n = 38 chromosomes as 14M+8SM+6ST+8A and one pair of sexual chromosomes. An heteromorphic secondary constriction, associated with the nucleolar organizer region (NOR), was seen on the long arms of chromosome pair 17. The C-banding technique revealed heterochromatin in the centromeric region of all the chromosomes and the NOR was C-banding positive. The giant otter presented the same diploid number as most mustelids, although its karyotype is quite species-specific.Key words: Amazon, aquatic mammals, ariranha, karyotype.Received: January 9, 2007; Accepted: February 7, 2007. There are five Amazonian aquatic mammals, the Amazonian manatee (Trichechus inunguis), the pink dolphin (Inia geoffrensis), the tucuxi (Sotalia fluviatilis), the Neotropical otter (Lontra longicaudis) and the giant otter (Pteronura brasiliensis). The World Conservation Union (IUCN) classifies the Amazonian manatee and the pink dolphin as vulnerable and the tucuxi and the neotropical otter as belonging to the "data deficient" category, while the giant otter is classified as an endangered species (IUCN, 2006). Riverine habitats are highly vulnerable to anthropogenic activities, this being especially true in the Amazon basin, which is suffering rapid development leading to degradation and loss of essential habitats for giant otters (Borobia and Rosas, 1991;Rosas, 1994;Carter and Rosas, 1997).The giant otter, Pteronura brasiliensis Zimmermann 1780 (Carnivora, Mustelidae, Lutrinae), is the largest of all otters and is endemic to South America, with historical records of sightings from north to south-central South America. However, currently stable populations are limited to the Amazon basin and upper Pantanal in the Paraná-Paraguay river basin (Carter and Rosas, 1997). Two P. brasiliensis subspecies have been cited in the literature but are of doubtful value (Duplaix, 1980). Karyotypic studies have been carried out to analyze intra-and interspecific and intra-and interpopulation variations as well as to identify cryptic species, mutagenic effects and to solve taxonomic problems (Guerra, 1988;Macgregor, 1993). Nie et al. (2002) used chromosomal rearrangements, a rare type of genomic change, to investigate some systematic questions relating to the genome phylogeny of the domestic cat, red panda and five mustelid species. However, while cytogenetic studies have previously been carried out on other mustelid species (Freitas et al., 1975;Kurose et al., 2000;Graphodatsky et al., 2002) there have been no published studies on the chromosomal constitution of P. brasiliensi...

Advances in the study of giant otter (Pteronura brasiliensis): ecology, behavior, and conservation: a review

“…According to Franco-de-Sá et al (2007) the diploid number of chromosomes in giant otters is 2n=38, which is in agreement with more than 60% of the Mustelidae family members. However, although mustelid karyotypes are conserved in regard to diploid number they present considerable differences in chromosome structure, indicating that several rearrangements occurred during the evolution of this group.…”

“…However, although mustelid karyotypes are conserved in regard to diploid number they present considerable differences in chromosome structure, indicating that several rearrangements occurred during the evolution of this group. Thirty-six of the giant otter chromosomes were autosomes (14 metacentric + 8 submetacentric + 6 subtelocentric + 8 acrocentric) and two sex chromosomes (Franco-de-Sá et al, 2007).…”

Fifty Years of Research on European Mink Mustela lutreola L., 1761 Genetics: Where Are We Now in Studies on One of the Most Endangered Mammals?

“…The diploid number of the chromosomes of European mink is 38, which is typical for many species of the Mustelidae Fischer, 1817 family; for more than 60% of species of this group, 2 n = 38 [ 39 , 40 ]. Among the representatives of the Mustela L., 1758 genus, the diploid number of chromosomes ranges from 38 to 44 [ 41 , 42 ].…”

“…The X chromosome is submetacentric, while the Y chromosome is metacentric [ 18 ]. As with other representatives of the Mustelidae family, the Y chromosome is the smallest one [ 40 ]. The fundamental number ( FN , number of chromosomal arms) is 62, while the fundamental autosomal number ( FNa , number of autosomal arms) is 58 [ 16 ].…”

“…Nucleolus organizer regions (NORs) were identified in one pair of telocentric chromosomes [ 16 ]. The standard pattern of European mink karyotype is not currently established [ 40 ].…”